RULES FOR
CLASSIFICATION OF
MOBILE OFFSHORE UNITS
STRUCTURES AND EQUIPMENT
MAIN CLASS
PART 3 CHAPTER 2
SPECIAL DESIGNS,
EQUIPMENT AND ST ABILITY
JULY 1995
SECTIONS
1
2
3
4
5
6
7
PAGE
General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Column-Stabilized Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Self-El\!vating Units ............................................................................................ 5
Steering Arrangements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Mooring and Towing Equipment .......................................................................... 18
Stability .......................................................................................................... 31
Watertight Integrity, Freeboard and Weathertight Closing Appliances ............................ 38
APPENDICES
A Closing Arrangements for Doors and Hatches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
DET NORSKE VERITAS CLASSIFICATION AS
Veritasveien !, N-1322 Hm>ik, Norway Tel.: +47 67 57 99 00 Fax: +47 67 57 99 11
CHANGES IN THE RULES
General
Main changes
• Sec.6 Stability
The present edition of the Rules includes additions and amendments
decided by the Board as of June 1995, and supersedes the July 1990
edition of the same chapter.
- This section has been updated and harmonized with the stability
parts of the 1989 IMO MODU Code.
- Item A201 is amended.
- Item A207 is new. New A211 is amended, A214 and A215 are
added.
- Item A301 5) is amended.
- New item A304 on inclining test procedure is added.
- Item BlOl is amended.
- Items B103 to B106 <ire amended.
- Items B200 to B600 are completely rewritten, and previous B500
to B1300 are renumbered.
- Items B702 and B902 are amended.
The Rule changes come into force on 1st of January l996.
This chapter is valid until superseded by a revised chapter. Supplements will not be issued except for an updated list of minor
amendments and corrections presented in the introduction booklet.
The introduction booklet is normally revised in January and July
each year.
Corrections and Clarifications
Revised chapters will be forwarded to all subscribers to the Rules.
Buyers of reprints are advised to check the updated list of Rule
chapters printed in the introduction booklet to ensure that the chapter
is current.
In addition to the above stated rule amendments, some detected errors have been corrected, and some clarifications have been made
in the existing rule wording.
© Det Norske Veritas
Computer Typesetting by Division Ship and Offshore, Det Norske Veritas Classification AS
Printed in Norway by Det Norske Veritas July 1995
7.95.2000
It is agreed that save as provided below Det Norslc:e Veritas, its subsidiaries, bodies, officers, directors, employees and agents shall have no liability for any loss, damage or expense
b~e~~~ 1 ;u~iu~!~s~~e;,i~t ~h~n~~~~~lio~ o\h~~~~i~:!1fg~~~;~~g!Wf~i ~:~~~d~fc-:'~~r~~!Y'1o ~e~~i~~1~Ji:~t0r s~~i~i~x~c~fi~ ~'ffi~:r~'o~ngl~tdmr~k~~e~ft~~~Thi: ~~;ii~~u:e~~~~fens~u~~
2
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0
byh6~tig~ ~eh~fi'~f 1' en;ff!:rs°i:ee0~~i~=· h~ ~~,!~1.:e~,a~y:n~ ;~;ho;'~~ ~h! ~~;::~~~~fit~!t~~r~lc:~ ~~~~~;ro~ i\~ir~ug:~Yarie~ ~ra~e~~;e~n°~~~i~~~~i~~c~~d~s ;,1j~fo~~~~!~~mg~~~~ g~eo~
0
*
0
on behalf of thorn and in consequence suffers a loss, damage or expense proved to be due to their negligence, omission or default, then Det Norslc:e Veritas will pay by way of comIn the event Det Norslc:e Veritas or its subsidiaries may be hold liable in accordance with the sections above, the amount
pensation to such person a sum representing his proved loss.
Under no circumstanc'es
of compensation shall under no circumstances exceed the amount of the fee, if any, charged for that particular service, decision, advice or information.
whatsoever shall the individual or lndividuals who have personally caused the loss, damage or expense be he!d liable.
In the event that any provision in this section shall be invalid
under the law of any jurisdiction, tho validity of the remaining provislons shall not in any way be affected.
*
*
CONTENTS
SEC. 1
GENERAL REQUIREMENTS .. ....... ...... ....... 1
A. Classification . . . .. . . . . .. . . . . .. . . . . . . .. . . . . .. . . . . . . .. . . . . . .. . . . . •• . . 1
A 100 Application . . . . . . . .. . . . . . .. . . . . .. . . . . . . . .. . . . ..
I
B 300
B 400
B 500
Bearing materials
........... .
Certificates . . . . . . . . . . ........................... .
. ......... .
Heat treatment . .. . .. .. .. .. . .
10
JO
10
C. Arrangement and Details ....•... .. ...... .. .....•.. .. ...•.. ... 10
B. Definitions ... ....... ...... ...... .. ...... ...... ......... ...... ...... 1
B 100 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . 1
C 100
C 200
C. Documentation .••.. ...•.. ...... ...... ........ ....... ........ ...... 1
C 100 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
D. Design Loads and Stress Analysis .•... .. ..••.•.. ..••.. .. ... 11
D JOO Rudder force . .. ..
. . . .. .. .. . ... ... .. . . .. 11
SEC. 2
D 200
D 300
COLUMN-STABILIZED UNITS ................... 2
A. General . . .. .. . . .. .. . . . . .. . . . . .. . . . . .. . . . . .. .. . . . . . .• . . . . •. . . . . •• •• . . 2
A 100
A 200
Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
B. Air Gap .••....••....••....•••...••.•............................... 2
B 100 General . . . . . . . . . . . . . . . . . . . . . . .
.. .... .. ..... .. .... .. ..
2
C. Design Loads ..... ...... .. ...... ...... ........ ..••.. .•.••.. ..••.. .. 2
C 100
Design and loading conditions . . .. . . . . . . . . . . . . . . .
2
D. Overall Strength . ..••.. ..••.. ..•.••.. ...•.. ........ ....... ...... .. 2
D 100
D 200
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Operation and survival . . . . . . . . . . . . . . . . . . .. . . . . .. . . . . . . . . . 2
D 300
Transit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Sternframes and rudders . . . . . . . . . . .
10
Steering gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Rudder torques .
Stress analysis . . .
.. . . . . . . . . . . . . .
11
. . . . 11
E. Sternframes ..... ........ .. .. ...... .. ...... .. ......... .. ..••.. ..•.
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. .... .. ... ...
E 200 Propeller posts
.. .. .... .. .. ... ... .. ... ... .. .... .. .
E 300 Sole pieces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
11
11
12
F.
F
F
F
F
F
12
12
12
13
E 100
Rudder Nozzles ...•.••......•..................................••
100 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . .
200 Nozzle and rudder fin plating . . . . . . . . . . . . . . . . . . . . . . . . .
300 Web plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
400
Section modulus
500
Welding
. . . . . . . . . . .. . . . . . . .. . . . . . .. . . . .. 13
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
G. Rudder Stocks and Pin ties . .. ......... ........ .. ..••.. .. ..••. 13
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
G JOO General . .. . . . . . . . . . . .
G 200
Rudder stock with couplings .
E. Local Strength . . . . . .. . . . . .. . . . . .. . . . . . . •• . . . . •• . •. . .• . •• . . . . . •. . . . 3
E 100 General . . . . . . . . . . . . . . . .. . . .
.... .. .... .. .... 3
E 200 Deck ....................................................... 3
G 300
G 400
Bearings . . .. .. .. . ... .. ..
14
Pintles . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
E
E
E
E
H. Steering Gears .. ..••••.. .. ..••.. .. ..•.••.. .. ..••.•.. ...••.. .. .... 15
300
400
500
600
Columns . . .
Pontoons
... .. .... .. .. .... .. ..
Bracings . . . . . . . . . . . . . . . .
Lifeboat platforms . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . .
3
3
3
4
F. Resistance Against Collision, Dropped Objects, Fire and
Explosion . . . .. ... . . . . •• . . . . •• . . . . •• . . . . . . .. . . . . .. . . . . ... . . . . . . . . . . . . 4
F 100 General . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . 4
SEC. 3
.. . . . . . .. . . . . . 13
H 100
H 200
General . .. .. .. .. .. .. .. .. .. .... .. .. .... .. .. ..
15
Steering capacity .. . . . . . . .. . . . . . . . . .. . . . . . .. . . . . . . . . . . . . . . 15
H 300
Power supply .. .. . . .. .. . . . .. .. .. . ... .. .. ..
H 400
H 500
Actuator housing, rudder carrier ... .. .. .... .. ... . .. .. . 15
Tiller arms, rotor vanes, etc. . .... .. .. .... .. .. .... .. ... 16
15
H 600
Tiller boss . . . . . . . . . .
H 700
H 800
Remote control system .. . . . . . . . .. . . . . . . . .. . . . .. .. . . . . . . . 17
Monitoring . . . . . .. .. . . . . . . .. . . . . . . .. .. . . . . . . .. . . . . .
17
. . . . . .. . . . . . . .
16
SELF-ELEVATING UNITS ......................... 5
I. Testing .•....••••....•.••......••••....•.••.......••......••.....••. 17
A. General . . .. . . . . .. . . . . . . . . . . . . .. . . . . .. . . . . .. . . . . . . . .. . . . . •• . . . . •• . . . . 5
I
100
Stemframes . . . . . . .. . . . . . . . . .. . . . . . .
A 100
A 200
I
I
I
200
300
400
Rudder nozzles . . . . . . . . . . . . . . . . . . . .
Steering gears . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sea trials
. .... .. .. .... ... ..
Classification . . . . . . . . . . . . . . . . . . . . . . .. . . . . . .
References .. . . . . .. . . .
.. ..... .. .... .. ...
5
5
B. Air Gap •••....••....•.......•.....••....••.•.....••................ 5
B 100 General ........ , . .
.... .. .... .. ... . .. .. .... .. . 5
C. Design Loads ....... ...... ...... ...... .. ...... ...... ....... ...... .. 6
C 100
Design and loading conditions . . . . . . . . . . . .. . . . . .. . . . . .. . 6
D. Overall Strength ... ...... ...... .. ...... ...... ............... .... .. 6
D 100
D 200
D 400
General
6
Operation and survival . . . . . . . . . . . . . . .
6
Tu~ ............................................. 7
Installation and retrieval . . . . . . . . . . . .
7
E.
E
E
E
Strength .............................•.....••.....••.....•..
General . . . . . . . . . . . .
.. .. .... .. ... .... .. .... .. .... ..
Hull . ......................
Legs .................
..............
7
7
7
7
Bottom mat and spuds
8
DLocal
100
200
300
E 400
. .. . . . . .. . . .
F. Overturning Stability on the Sea Bed ... ... .... .. ..••.. ...•. 8
F I 00 General . . . . . . . . . . . . . . . . . . . .
8
G. Resistance Against Collision, Dropped Objects, Fire and
Explosion . . . •• . . . . . .. . . . . .. . . . . . . .. . . . . .. . . . . . . .. . . . . ... . . . . . . . . . . . . 8
G 100 General
... .. ... ... .. ... .. .. .... .. .... .. .... .. .... 8
SEC. 4
STEERING ARRANGEMENTS .••....••....••..... 9
A. General •. . . . . •. . . . . . . •• . . . . •• . . . . •• •• . . . . •• . . . . . . . •• . . . . •• . . . . •• . . . . 9
A 100 Scope ........ .'..
. .. . . . . . . . .
9
A 200
A 300
Definitions . . . .
Documentation .. . . .
.. . . .. . . . . . . . .. .. . .. .. . . .
.. . . . . . . . . . .
9
9
B. Materials ....•..•....••....•.......••.............................. 10
B I 00
B 200
Plates and sections . . .
Forgings and cast.ings . . . . . . . .. . . . .
10
10
SEC. 5
17
17
17
17
MOORING AND TOWING EQUIPMENT ..... 18
A. General . . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . .. . . . . .. 18
A 100 Scope .. .. .. . .. . .. .. .. . . . . .. ..
. ... .. .. . . .. .. .. . . .. 18
A 200
A 300
Definitions . .. . . . . . .. .. . . . . . .. .. . . . . . .. . . . . . . .. .. . . . . . .. . . 18
Documentation .. ..
18
B. Structural Arrangement for Mooring Equipment ...... 19
B 100 General ............... .
. ..................... 19
C. Equipment Specification .. ......... .. ...... .. ........ ...... ... 20
C 100
C 200
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Equipment number
20
D. Anchors ...... .. .. ........ ........ .. ...... .. ... ...... .. ...... ..•... 21
D 100
General
D 200
D 300
Materials . . . . . . . . . . . . . . . . .
Anchor shackle . . . . . . . . . . . .
D 400
D 500
Proof testing of anchor strength . . .. . .. .. . . . . .. .. . . . 22
Additional requirements for H.H.P. («High Holding
Power») anchors
. . . . . . 22
Identification .. . . . . . .. .. . . . .
23
D 600
. .. .. .. .. .. . . .. .. .. .. .
.. ............. 21
E. Mooring Chain and Accessories .. .................. ...... ...
E 100 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
E 200 Materials . . . . . . . . . . . . . . . . . . . . .
E 300
Heat tr~tment and mechanical testing of chain and
accessones ............................................... .
E 400
Loading test ...................... .
E 500
Proof load test ......... .
E 600 Dimensions and tolerances ....
E 700
Non-destructive testing (NDT)
E 800 Repair
..................... .
E 900 Identification and documentation ..................... .
22
22
23
23
23
23
24
24
25
26
26
26
F. Steel Wire Ropes ••....••....••.................................. 26
F 100
F 200
F 300
General . . . . . . . . . . . . . . . . . . . . . . . .
Materials . ... .. .. .. .. .. .. .. .. ..
Testing of steel wire ropes . .
SEC. 7
26
.. .................... 27
27
WATERTIGHT INTEGRITY, FREEBOARD
AND WEATHERTIGHT CLOSING APPLIANCES ........................••.•....••................. 38
A. General . .. . . . . .. . . . . . . .. . . . . . . . . . . . . . . . . .• . . . . . . . •• . . . . . . .. . . . . .. . . 38
G. Windlass and Chain Stoppers . . . . •• . . . . . •• . . . . . . •• . . .• . . . . . . 28
G 100
G 200
G 300
General design . . . . . . . . . . . . . . . . . . . . . . .
28
Materials . .
. . . . . . . . . . . . . . . . . . . . . . . 28
Testing . . . . . . . . . . . . . . . . . . . . . .
. . . . 28
H. Fairleads . . . . . . .• . . . . •• . . . . •• . . . . •• . . . . . . . . . . . . . . . . . .. . . . . .. . . . . .. . 29
H 100
H 200
H 300
General design . . . . . . . . . . .
Materials . . . . . . . . . . . . . . . . . .
Strength and design load
... .. .... ..
.... .. .... ..
29
29
29
A 100
A 200
A 300
General . . . . . . . . . . . . . . . . . . .
29
Material . . . . . .
. . . . . . . . . . . . . . . . . . . . . 30
Strength
.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
30
J. Arrangement and Devices for Towing . .. . . . . .. . . . . .. . . . . .. 30
J
100
200
300
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Material . . . . . . . . . . . . . . . . . . . . .
30
Strength analysis . . . . . . . . . . . . . . . . .. . . . . .. . . . . .. . . . . .. . . . . 30
SEC. 6
STABILITY ............................................. 31
J
J
38
38
38
B. Watertight Int<grity ..............................•............. 38
B
B
B
B
B
100
200
300
400
500
I. Wire End Attachments .. ..•... ..••.. .. .•.. .. .... .. ..••.. .•.•.. 29
1 100
I 200
1 300
Application . . . . . . . . . . . . . . .
. .... .. .. .... ..
Definitions . . . . . .
. . . . . . . . . . . . . . . . . .. . . . .
Documentation
... .. ... ... .. ... ... .
General ..................................................
Internal openings . . . .
.. . . . . . . . . . . . . . . . . . .
External openings . . . . . . . . . . . .. . . . . . . .. . . . . . . . . . . . . . . . . . .
Strength of watertight doors and hatches . . . . .
Operation and control of watertight doors and
hatches ....................................................
38
39
39
39
40
C. Freeboard ...............•......••......••......................... 40
C 100
C 200
C 300
General . . . .
. .. . . . . . . .. . . . . . . . . . . . . .
Self-elevating units . . . . . . . . . . . .
Column-stabilized units . . . . . . . . .. . . . . . .. . . . . .. . . . . .
40
40
40
D. Weathertight Closing Appliances ....................••..... 41
D
D
D
D
100
200
300
400
General
. .. .. .. .. .. . . .. .. .. . . .. .. ..
Weathertight doors .....................................
Weathertight hatches and coamings ...................
Gaskets and closing devices .. . . . . . . . . . . . .. . . . . . . . . . . .
41
41
41
41
A. General .... .. .... .. .... .. ...... .... ........ ....... ...... ...... ..... 31
E. Ventilators and Air Pipes .. ..••.. .. ..••.. .. ...... .. .... .. ..... 42
A
A
A
A
F. Inlets, Discharges and Scuppers .•... .. ...... .. ...... ....... 42
100
200
300
400
Scope ......................................................
Definitions
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
Documentation for approval . . . . . . . . . . . . . . . . . . . . . . . . . .
Documentation for information . . . . . . . . . . . . . . . . . . . . . . .
31
31
32
33
B. Assumptions and Criteria .. ...... ...... .. .... .. ...... .... .... 33
B
B
B
B
B
B
B
B
B
100
200
300
400
500
600
700
800
900
B 1000
B 1100
B 1200
B 1300
B 1400
B 1500
B 1600
Righting moment and heeling moment curves ......
Intact stability criteria . . . . . .. . . . . .. . . . . . . . . . . . . . . . .. . . .
Damage stability - self-elevating units . . . . . . . . . . . . . . .
Damage stability - column-stabilized units . .
Damage stability - all types of units . . . . . . . . . . . . . . . . . .
Extent of damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chain lockers . .. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Load line and draught marks .. . . . . . . . . . . . . . . . . . . . . . . . .
Extent of watertight/weathertight closing of external
openings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Internal watertight intergrity and subdivision . . . .
Maximum allowable VCG-curves, columnstabilized units . .
. . . . . .. . . . . .. . . . . .. . . . . .. . . . . . . . . . .
Maximum allowable VCG-curves, self-elevating
units . .. .... .. .... .. .. .. .. .... .. ..
.. ...........
Inclining test and lightweight . . . . . . . . . . . . . . . . . . . . . . . . . .
Loading conditions, column-stabilized units . ... ....
Stability manual or the stability part of the Operation Manuals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stability requirements for heavy lift operations .....
33
34
35
35
35
35
36
36
E 100
F 100
F 200
F 300
General . .. ..
.. . .. . .. .. . .. . .. .. . .. .. .. . . ... .. .. . . .. .
42
Sea inlets and discharges in closed systems ......... 42
42
Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Scuppers . . . . . . . .
G. Side Scuttles and Windows . .. ....... .. ...... ...... .. ..•... ... 43
G 100
General
.. ... .. .... .. .. .... ... .. .... .
43
H. Testing of Doors and Hatches . ... .. ..••.. ..•••. .. ...... ..... 43
H 100
H 200
H 300
Pressure testing of watertight doors and hatches . . 43
Hose testing of watertight and weathertight doors
and hatches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Function testing of watertight doors and hatches . 43
36
36
APP. A
36
A. Waterlines •. . . . . . . . . . . . .. .. . . . . .. .. . . . . .. .. . . . . ... . . . . . . .. . . . . .. . . 44
A 100
CLOSING ARRANGEMENTS FOR DOORS
AND HATCHES .. .. ...... .. ...... .. ...... ...... .. ..... 44
Description of waterlines . ... .. .. .. .. .. .. .. .. .. .
44
37
37
37
B. Opening Location . ....... .. ...... .. ..•... .. ..••.. .. .... .. ....... 44
37
37
C. Operation and Locking ......... .. ...... ...... .. ...... .. .... ... 44
B 100
C 100
Description of location of openings .................. 44
General requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
44
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.1 - Page 1
SECTION 1
GENERAL REQUIREMENTS
Contents
102 Necessary strengthening of the hull structure due to
loads imposed _by the equipment and installations are given
where appropnate.
A. Classification
A 100
Application
B. Definitions
B. Definitions
B 100
Symbols
B 100
101
C. Documentation
C 100
General
"f
=
Symbols
Specified minimum upper yield stress of the material
in N/mm2 .
A. Classification
A 100
C. Documentation
Application
101 The Rules in this Chapter apply to special platform
design including steering arrangement if relevant, mooring
and towing equipment and to the stability requirements as
required for the assignment of main class.
C 100 General
101 Plans and particulars to be submitted for approval or
information are specified in the respective Sections of this
Chapter.
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 2 - P1.3 Ch.2 Sec.2
SECTION2
COLUMN-STABILIZED UNITS
Contents
C. Design Loads
A. General
A 100 Classification
A 200 References
C 100
101 The general definition of design conditions is given in
Ch.I Sec.3 AIOO whilst the loading conditions within each
design condition are defined in Ch. I Sec.4 A300.
B. Air Gap
B I 00 General
102 The relevant design and loading conditions for column-stabilized units are shown in Table Cl.
C. Design Loads
C 100
Design and loading conditions
Design and loading conditions
Table Cl Relevant design and loading conditions
D.
D
D
D
Overall Strength
100
200
300
300
400
500
600
a)
Installation
Operation
Retrieval
Survival
Transit
E. Local Strength
E 100 General
E 200 Deck
E
E
E
E
Loading condition:;
Design conditions
References
Operation and survival
Transit
Columns
Pontoons
Bracings
Lifeboat platforms
F. Resistance Against Collision, Dropped Objects, Fire and
Explosion
F 100 General
b)
x
x
x
x
x
x
c)
x
d)
x
e)
x
x
x
103 The accidental impact energy to be considered in
loading condition c) is defined in Ch. I Sec.4 E. If a reduced
impact energy is considered for collision, the assumed
maximum size of visiting vessel is to be stated in the
~Appendix to the Classification Certificate».
104 A simplified evaluation of loading condition c) and d)
is shown in F.
A. General
A 100 Classification
101 Certain aspects regarding structnral design of column-stabilized units are emphasized in this Section.
102 If the unit is strengthened for resting on the sea bed
during operation, the additional class notation SUB will be
given.
Requirements to air gap, safety against overtnrning stability,
local reinforcement of bottom of pontoons, etc. will be
specially considered for the -t(resting on seabed» condition.
105 For loading condition e) the functional load component inplane with the deck at maximum heel in damaged
condition is to be account ed for.
Maximum allowable heel in damaged condition is 15 degrees. See Sec.6.
Special requirements are given for accommodation vessels
in damaged condition. See Pt.5 Ch.2.
Guidance note:
The heeled condition corresponding to accidental flooding in
transit conditions will normally not be governing.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
A 200 References
201 The general requirements to structural design are
D. Overall Strength
given in Ch.!.
D 100
References
101 Definition of overall and local forces are given rn
Ch. I Sec.4 A.
B. Air Gap
B 100 General
D 200
101 Clearance between the deck structure and the wave
crest is normally to be ensured for operating and survival
conditions taking into account the motion of the unit. The
distance between the lower part of the deck or heavy attachments and the crest of the maximum design wave is to
be positive.
A negative distance may be accepted if wave impact forces
on the deck structnre are taken into account in the strength
analysis.
201
Operation and survival
The structural analysis is to be carried out by means
of space frame or finite element models. The model is to
represent properly the stiffness properties of the unit. The
support conditions for the model are not to cause any artificial restraint on the structural response.
Guidance note:
The effect of local variation of element properties and cut-outs
may normally be accounted for by evaluation of the stresses
based on the calculated distribution of overall forces and moments.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.2 -
202 Depending on how coarse the mathematical model of
the unit is, more or less of the local forces will be included
in the results obtained from the overall strength calculations.
In general, both the overall and the local forces are to be
considered when determining the actual stresses.
203 The overturning moment due to sustained wind forces
may normally be assumed counterbalanced by proper ballast
distribution and mooring forces.
Guidance note:
The mooring forces will normally not have any significant influence on the overall structural response, but may have a significant local effect on the columns.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
D 300
Transit
301 The structure is to be analysed for zero forward speed.
For high speed vessels also maximum speed is to be considered in the load and strength calculations.
Guidance note:
Roll and pitch motion at resonance will normally be somewhat
smaller than calculated by a linear wave theory due to flow of
water on top of the pontoons. This effect may be accounted for
provided its magnitude is documented by rational analysis or
tests.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
302 Slamming on bracings is to be considered as a possible limiting criterion for operation in transit. The effect of
fotward speed is to be accounted for.
E. Local Strength
E 100
101
102 The scaptlings are to be checked against the maximum
local forces superimposed on the overall forces. Explicite
requirements to scantlings of plates, stiffeners and girders
are given in Ch. I Sec.6 and 7 based on design loads given
in Ch. I Sec.4.
Requirements to weld connections are given in Ch. I Sec.8.
Deck
201 If the deck is built up by heavy main girders with thin
deck plating in-between, only the main girders and the stiffeners of the thin decks need satisfy the buckling requirements. The contribution by the thin deck to the global
strength is to account for the reduced buckling strength.
Guidance note:
For calculation of effective flange of main girders reference is
made to 3.4.4 in Classification Notes on «Buckling Strength
Analysis»:
The width of the thin plating within the effective flange breadth
of the main girders is to be multiplied by the factor:
IX
= exp for stiffeners parallel with girder
2
=•p
~ +0,1 (1- ~ )(1+ ;2)
for stiffeners perpendicular to girder
where
1,8
0,8
•p=p- P2
=
1,oror
for
P?: 1,0
P< 1,0
P=.E...t -VT
fUf
distance between stiffeners.
=
= free span length of stiffeners.
= plate thickness.
= Young's modulus.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
202 Where steps in thickness of more than 4 mm occur in
deck plates, the thicker plate is normally to be sniped (30°)
at butt welds across the flange of main girders and in corners
between main girder flanges where thin deck plating is attached. In the latter case the comer may alternatively be
softened by inplane brackets.
203 In load case d) with loss of a bracing supporting the
deck, local yielding and buckling may occur in one main
girder. This is acceptable provided the load exceeding the
plastic capacity of that girder is transmitted to other members without exceeding the allowable stresses.
Guidance note:
In order to account for the redistribution properties of the deck
it is advised to include major secondary structures, such as drill
floor substructure with derrick, in the overall strength model.
---e-n-d---o-f---G-u-i-d-a -n-c-e--- n-o-t-e---
E 300
Colwnns
301 The internal structure in the columns supporting the
bracings is normally not to be weaker than the axial strength
of the bracing itself.
302 If the bracing forces are transmitted to the column
shell, the resulting stresses in the column shell are to be
combined with the overall forces and hydrostatic pressure
for strength control of the shell.
E 400
General
Reference is made to Ch. I Sec.3 A500.
E 200
b
a
t
E
Page 3
Pontoons
401 The pontoons are to be checked for overall bending
and shear as well as axial forces due to end pressure combined with local hydrostatic pressure.
402 Special attention is to be paid to the pontoon strength
in way of intersections with colunms, accounting for any
reduction in cross section strength due to cut-outs and stress
c oncentrations.
403 The scantlings in tanks are to be checked for both full
and empty tanks irrespective of the actual load plan. An
exception is made for control of damaged condition with loss
of one column's buoyancy for accommodation units where
tanks which are always full in operating conditions, need not
be checked as empty.
E 500
Bracings
501 Bracings are normally to be made watertight with access for internal inspection in operating conditions. Leak
detection devices are to be fitted either remotely operated
or as a coq at the bottom of the end bulkhead.
Guidance note:
It is advised that if the latter solution is chosen, access to the
bracing should be possible through permanently dry spaces.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
502 Bracings are to be checked against fatigue. Stress
concentrations are to be avoided as far as possible. Smooth
transmission of forces is to be ensured at the support regions. Cut-outs are normally to be avoided in the shell. Attachments are to be welded on doubling plates of 8-10 mm
thickness with well rounded corners.
503 Bracings are to be checked against buckling due to
combined axial stresses and hoop stresses caused by external
hydrostatic pressure. Ring stiffeners are to be fitted when
necessary.
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 4 - Pt.3 Ch.2 Sec.2
E 600 Lifeboat platforms
601 Lifeboat platforms are to be checked for the loading
conditions a), b), and e) (see Pt.3 Ch.I Sec.4 A300). A
dynamic factor of 0,2 g due to retardation of the lifeboats
when lowered is to be included.
Guidance note:
Stren~h analysis methods for lifeboat platforms are given in
Classification Note No. 31.4 «Strength Analysis of Main Structures of Column-Stabilized Units~.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
F. Resistance Against Collision, Dropped Objects, Fire and Explosion
F 100 General
101 The general basis for estimating the effect of credible
collision and dropped object is given in Ch. I Sec.4 E.
102 The credible collision against a column of columnstabilized units will normally only cause local damage of the
column, i.e. loading condition c) and d) need not be
checked. In cases with specially slender columns, however,
the global strength of the unit at the moment of collision is
to be checked according to Ch. I Sec.5 D700 and the residual strength after collision according to Ch. I Sec.5 D800.
103 The credible collision or dropped object against a
bracing will normally cause complete failure of the bracing,
which then is to be assumed non-effective for check of the
residual strength of the unit after collision, i.e. loading
condition d).
For specially strong bracings, the damage may be limited to
local denting. According to Ch. I Sec.3 A600 the residual
strength of the bracing may be included for check of the unit
after the accident.
104 The structural arrangement of the upper hull is to be
considered with regard to the structural integrity of the unit
after the failure of relevant parts of any primary structural
element essential for the overall integrity caused by fire or
explosion. Where considered necessary by the Society, a
structural analysis may be required with strength criteria as
loading condition d).
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.3 - Page 5
SECTION 3
SELF-ELEVATING UNITS
Contents
A. General
A. General
A 100
A 200
A 100 Classification
101 Certain aspects regarding structural design of self-
Classification
References
elevating units are emphasized m this Section.
B. Air Gap
B 100 General
A 200 References
201 The general requirements to structural design are
given in Ch. I.
C. Design Loads
C 100 Design and loading conditions
D.
D
D
D
D
B. Air Gap
Overall Strength
100
200
300
400
General
Operation and survival
Transit
Installation and retrieval
B 100 General
101 Clearance between the hull structure and the wave
crest is normally to be ensured for the operating position.
The requirement to the length of the leg is: Tlie distance
between the lower part of the deck structure in operating
E. Local Strength
E
E
E
E
100
200
300
400
position and the crest of the maximum design wave, includ--
General
Hull
Legs
Bottom mat and spuds
mg astronomical and storm tides, is not to be less than 10
per cent of the combined storm tide, astronomical tide and
height of the design wave above the mean low water level,
or 1,2 metre, whichever is the smaller. Expected subsidence
of the structure is to be taken into account.
A smaller distance may be accepted if wave impact forces
on the deck structure are taken mto account in the strength
and overturning analysis.
Crest elevation above still water level is given in Fig. 1.
102 Clearance between the structure and wave is to be
ensured in floating condition for appendices such as helicopter deck, etc.
F. Overturning Stability on the Sea Bed
F
100
General
G.
R~istance
Against Collision, Dropped Objects, Fire and
Explosion
G 100 General
~.
"YJo CREST
H
1-0 -
~
-
~ ~ -+--~-+-+-+-+-+-t-t--
n-\~"'No~N~
\
' ~ ~ ~.. ~ ~
a>
ELEVATION
H
WAVE
T
WAVE PERIOD
h
STJL~-
ABOVE STILL WATER
HEIGHT
WATER
METRES
METRES
SECONDS
DEPTH
-·-· ,..----·
METRES
I
:'1
,9
1---+,t-\-t\\--\t-\-+-\ f-\+'+,'~,\,,.,\.±-:~ N ~ ~
.8
r---i-\-\-t--\-\f-1\..-t-ft':+-H'++\--\-\!-\+\t-'\--iT-\\-t\:\--1'..:.~ K'-
+-\--'
.7
\
\ \
.oos
.009 .012
' ' \\
.018
.03
\
.06
\ ' I\ [\.["\ ~ ~ ~
.09 .12
.18
Fig. 1
Crest elevation
DET NORSKE VERITAS
.3
.6
.9
\.2
1.B
3
Rules for Mobile Offshore Units , July 1995
Page 6 - Pt.3 Ch.2 Sec.3
C. Design Loads
C 100 Design and loading conditions
101 The general definition of design conditions is given in
Ch. I Sec.3 AlOO whilst the loading conditions within each
design condition are defined in Ch. I Sec.4 A300.
102 The relevant design and loading conditions for selfelevating units are shown in Table Cl.
Table Cl Relevant design and loading conditions
a)
b)
x
x
x
x
x
Installation
x
Operation
Retrieval
x
x
Survival
Transit
c)
x
d)
e)
Guidance note:
The heeled conditions corresponding to accidental flooding will
normally not be governing for a self-elevating unit.
x
---e-n-d---o-f---G-u-i-d-a-n-c-e--n-o-t-e---
x
D. Overall Strength
103 The maximum permissible rigid body motions of the
unit while elevating or lowering legs are to be specified in
the +:Appendix to Classification Certificate». The design environmental loads for these design conditions are to be determined on the basis of these limiting conditions.
104 Units with separate footings which are designed for a
pinned leg-bottom connection are to have a capability to
preload the legs up to at least 100 % of the maximum design
axial loads in the legs accounting for functional loads and
environmental overturning loads. The required preload and
maximum permissible environmental data during preloading
are to be stated in the •Appendix to Classification
Certificate».
105 Units with separate footings where the design is based
on a specified moment restraint of the legs at the sea bottom
are to have a capability to preload the legs up to a level
which shall account for the maximum design axial loads in
the legs due to functional loads and environmental overturning loads pluss the specified moment restraint at the
bottom.
In lieu of a detailed soil/structure interaction analysis the
required preload may in this case be determined by the following factor:
·
For cohesive soils, e.g. clay:
Fyp
Fy
D 100 General
101 The corresponding values of environmental design
data, headings of environmental loads, water depths, hull
elevation, soil penetration, and soil leg interaction are to be
specified in the ~Appendix to Classification Certificate».
102 For each environmental condition where a minimum
restraint moment of the legs at the sea bottom has been taken
into account in the design, an additional reference environmental condition is to be considered where the legs are assumed pinned at the sea bottom. The reference conditions
are also to be specified in the •Appendix to the Classification
Certificate».
D 200 Operation and survival
201 Dynamic amplification of the structural deflection and
stresses due to wave loading is to be accounted for if the
natural periods of the unit are such that significant amplification may occur.
202 Non-linear amplification of the overall deflections due
to second order bending effects of the legs are to be accounted for whenever significant. The non-linear bending
response may be calculated by multiplying the linear leg response by an amplification factor
1
a=--"~-
1
2.[A
Mu
" R2
Fy
[-~'--=-
1-_f_
PE
P
= static axial load on one leg
PE = Euler buckling load for one leg.
For cohesionless soils, e.g. sand:
2
FF':= (
106 The accidental impact energy to be considered in
loading condition c) is defined in Ch. I Sec.4 E. If a reduced
impact energy is considered for collision, the assumed
maximum size of the visiting vessel is to be stated in the
~Appendix to the Classification Certificate».
107 A simplified evaluation of loading condition c) and d)
is shown in G.
Loading conditions
Design conditions
tern is installed which will provide penetration to full soil
contact of the total spud-can area.
All parameters specified above and the maximum permissible environmental data during preloading are to be stated in
the •Appendix to the Classification Certificate».
203
The static inclinations of the legs defined as the static
angle between the leg and vertical line due to fabrication
tolerances and fixation system for the legs is to be accounted
for.
2}
!----
204 The leg/soil interaction is to be varied as necessary
" R2
Fvp = minimum required preload on one leg
Fv = maximum design axial load in the leg accounting for
functional loads and environmental overturning
loads.
Mu = minimum design moment restraint of the leg at the
sea bottom
A = area of spud-can in contact with soil
R = equivalent radius of spud can contact area.
For cohesionless soils, the above requirement to preload
capacity may be departed from in case where a jetting sys-
DET
within the design specifications to provide maximum stresses
in the legs, both at the bottom end and at the jackhouse
level.
205
Hydrodynamic coefficients as for smooth elements are
normally accepted, provided significant marine growth is
avoided and the wave loads are calculated in accordance
with Ch. l Sec.3 B306. Assumptions regarding allowable
marine growth are to be stated in the •Appendix to the
Classification Certificate•. Hydrodynamic coefficients are
shown in Ch. I Sec.4 C.
For cylindrical chords with racks, the drag coefficient may
be taken as (see Fig. 2):
NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.3 - Page 7
c 0 R = c 0 + 4 Dti.
Co
Li.
304 For the ocean transit condition the legs are to be designed for the following forces considered to act simultaneously:
cos a
is the drag coefficient for a smooth cylinder with diameter D, given in Ch. I Sec.4 C.
=a+b/2
Equivalent single beam hydrodynamic coefficients for lattice-type legs may be obtained from Classification note on
•Strength Analysis of Main Structures of Self-Elevating
Units».
120 % of the acceleration forces caused by the roll and
pitch of the platform
- 120% of the static forces at the maximum amplitude of
roll or pitch
- wind forces from a 45 m/sec wind velocity.
-
For design loads, see Ch.I Sec.3 A103.
Yield and buckling criteria are to be considered in accordance with Pt.3 Ch. I Sec.5 Load condition b), Environmental
loads and associated functional loads. In addition, fatigue
will have to be considered when a relevant design condition
is specified, e.g. as a specific transit route or sea state with
corresponding duration.
This will be stated in the
•Appendix to the Classification Certificate•.
Guidance note:
The specified criteria are to be considered only as reference values for evaluation of specific tows.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
305 Dynamic amplification of the acceleration forces on
the legs is to be accounted for if the natural periods of the
legs are such that significant amplification may occur.
306 If considered relevant, the effect of vortex shedding
induced vibrations of the legs due to wind is to be taken into
account.
D 400
401 In lieu of a more refined analysis, the maximum bottom impact force on a leg may be calculated as a horizontal
force
Fig. 2
Drag of cylindrical chords with racks
206 Equivalent single beam stiffuess parameters for lattice-type legs·may be obtained from Classification Note on
•Strength Analysis of Main Structures of Self-Elevating
Units».
D 300
Installation and retrieval
Transit
301 The leg positions for field moves and ocean moves are
to be specified in the •Appendix to the Classification
Certificate>1-. A field move is one that would require no more
e
= roll angle
T = roll period
E = Young's modulus
= effective moment of inertia of leg cross-section
I
IM
mass moment of inertia of jack-up with respect to
rolling
L
length of leg between bottom and support at the
barge.
than a 12-hour voyage to a location where the platform
could be elevated, or to a protected location.
E. Local Strength
302 For field ocean moves the following will be stated in
the •Appendix to the Classification Certificate.:
- Specified maximum environmental loading criteria, e.g.
as environmental data or motion response.
- Assumptions regarding reinforcements and sea fastenings.
- Assumptions regarding removal of structural equipment,
e.g. leg sections and helicopter deck.
Guidance note:
Only the principles and main data will be given since details are
assumed covered by the Operations Manual and considered by
the Marine Surveyor issuing the Towing Declaration for each
move.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
E 100
101
Reference is made to Ch. I Sec.3 A500.
E 200
Hull
201 Scantlings of the hull are to be checked for the transit
conditions with external hydrostatic pressure and inertia
forces on the legs as well as for the elevated conditions.
202 Special attention is to be paid to the means for the leg
support, the jackhouses, the support of the jackhouse to the
main hull, and the main load transfer girders between the
jackhouses.
E 300
303 For the field transit position the legs are to be designed for the acceleration forces caused by a 6 degree single amplitude roll or pitch at the natural period of the unit
plus 120 % of the static forces at a 6 degree inclination of the
legs unless otherwise verified by model tests or calculations.
General
Legs
301 The boundary conditions for the legs at the sea bottom
are to be varied within realistic upper and lower limits when
the scantlings of the legs are determined. The variation in
boundary conditions shall talce into account uncertainties in
the estimation of soil properties, non-linear soil-structure
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 8 -
Pt.3 Ch.2 Sec.3
interaction, effects due to repeated loadings, possible scour-
ing etc.
302 When determining the forces and moments in the legs,
different positions of supports along the legs are to be considered.
F. Overturning Stability on the Sea Bed
F 100 General
101 The safety against overturning 1s determined by the
equation:
F= Ms/Mo
303
Due attention is to be paid to the shear force in the leg
between supporting points in the hull structure, and the position and duration of load transfer between the leg and hull.
304
Lattice-type legs are to be checked against overall
buckling as well as buckling of single elements and punching strength of the nodes.
305 Units which are designed for areas with large wave
loads are normally to be checked against fatigue of the legs.
Ms = stabilizing moment, i.e. caused by functional loads
Mo = overturning moment, i.e. caused by environmental
loads.
102 The stabilizing moment due to functional loads should
be calculated with respect to the assumed axis of rotation.
For jack-ups with separate footings (spudcans) the axis of
rotation may, in lieu of a detailed soil-structure interacting
306
analysis, be assumed to be a horizontal axis intersecting the
into account the astronomical and storm tides.
axis of two of the legs. It may further be assumed that the
vertical position of the axis of rotation is located at a distance above the spudcan tip equivalent to the lesser of:
307 Bottom impact forces due to rigid body motions of the
unit while lowering the mat to bottom, are to be considered.
a) half the maximum predicted penetration, or,
b) half the height of the spudcan.
Any compartment which is not freely vented to the sea
when the mat or spud is resting on the sea bed, is to be designed for a head of water to the design water level, taking
See D 400.
E 400
Bottom mat and spuds
401
The legs may be designed to penetrate the sea bed or
be attached to spuds or to a mat which rests upon the sea
bed in the operation position and may augment the hull
buoyancy in the transit position.
402
In the operating condition account is to be taken of the
loads transferred from the legs and the sea bed reaction, and
the internal structure is to be designed to facilitate proper
diffusion of the loads.
403 High stress concentrations at the connection between
leg and mat/spud are to be avoided as far as possible.
404 The effect of an uneven distribution of critical contact
stresses over the foundation area is to be examined taking
into account a maximum eccentricity moment from the soil,
uneven seabed conditions and scouring.
For separate type spudcans the maximum eccentricity mo-
ment should normally not be taken less than:
M=0,5FyR
The corresponding critical contact pressure should normally
not be taken less than:
q=-
R2
=
maximum design axial load in the leg accounting for
functional loads and environmental overturning
loads.
R
=
unfavourable direction and combination of environmental
and functional loads according to the load plan for the unit.
The dynamic amplification of the combined wave/current
load effect should be taken into account.
104 The safety against overturning is to be at least 1, I.
105 The lower end of separate legs will have to be prevented from sideway slipping by ensuring sufficient horizontal leg/soil support. A statement to this effect will be
given in the Appendix to the Classification Certificate.
G. Resistance Against Collision, Dropped Objects, Fire and Explosion
G 100 General
101 The general basis for estimating the effect of credible
collision and dropped objects is given in Ch.! Sec.4 E.
102 Simplified procedures to evaluate the resistance
against collision and dropped objects are given in the Classification Note on •Strength Analysis of Main Structures of
Self-Elevating Units•.
Fy
Fv
For jack-up with mat support, the location of the axis of
rotation may have to be specially considered.
103 The overturning moment due to wind, waves and
current should be calculated with respect to the axis of rotation, defined in 102.
The overturning stability is to be calculated for the most
equivalent radius of spud-can contact area.
For other types of bottom support, e.g. mats special considerations should be made.
103 The structural arrangement of the upper hull is to be
considered with regard to the structural integrity of the unit
after the failure of relevant parts of any primary structural
element essential for the overall integrity caused by fire or
explosion. Where considered necessary by the Society, a
structural analysis may be required with strength criteria as
loading condition d).
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.4 - Page 9
SECTION 4
STEERING ARRANGEMENTS
Contents
103 Requirements to thrusters intended for manoeuvring
or positioning purposes are given in Pt.4 Ch.2.
A. General
A 100 Scope
A 200
A 300
104 For units with two or more pontoons, steering by the
propellers on the pontoons may be accepted after special
consideration. If there are no other means for steering, the
redundancy of the propulsion system is to be acceptable.
Definitions
Documentation
B. Materials
8
B
8
B
B
100
200
300
400
500
Plates and sections
Forgings and castings
Bearing materials
Certificates
Heat treatment
A 200 Definitions
201 Some terms used in this Section are indicated in Fig.
1, other terms are:
- Steering appliances are the machinery applying torque to
the rudder stock (e.g. tiller or rotor with power actuator)
and power units necessary for effecting movement of the
rudder.
- Remote steering systems are buttons, levers or wheels
on navigating bridge, connections to steering gear room
and control gear on power units. Any auto-steering system installed replacing any function of the operator is not
to be considered as part of the system.
- Redundancy, see Pt.4 Ch. I Sec. I.
- Independence, see Pt.4 Ch. I Sec. I.
- Power Unit is:
C. Arrangement and Details
C 100
C 200
Stemframes and rudders
Steering gear
D. Design Loads and Stress Analysis
D 100 Rudder force
D 200 Rudder torques
D 300
Stress analysis
E. Sternframes
General
E 100
E 200
E 300
Propeller posts
Sole pieces
1) an electric motor and its associated electrical equipment in case of electric steering gear;
F. Rudder Nozzles
F
F
F
F
F
100
200
300
400
500
2) an electric motor and its associated electrical equipment and connected pump with supply lines in case
of electrohydraulic steering gear;
General
Nozzle and rudder fin plating
Web plates
Section modulus
3) a driving engine and connected pump with supply lines
in case of other hydraulic steering gear
Welding
G. Rudder Stocks and Pintles
G 100
G 200
G 300
G 400
H.
H
H
H
H
H
H
H
H
I.
I
I
I
I
-
Rudder actuator is a device for applying torque to the
rudder stock (e.g. rotary vane actuator, hydraulic rams
or worm gearing).
- Remote control system, see Pt.4 Ch.5.
General
Rudder stock with couplings
Bearings
Pintles
Steering Gears
100 General
202
200
300
400
500
600
700
800
D =
fi =
FR =
FF =
MTR=
MTF=
Mrr=
Steering capacity
Power supply
Actuator housing, rudder carrier
Tiller arms, rotor vanes, etc.
Tiller boss
Remote control system
Monitoring
Symbols:
diameter of nozzle, mean, see Fig. 2
material factor, see B
design rudder force, nozzle, see D
design rudder force, fm, see D
design rudder torque, nozzle, see D
design rudder torque, fin, see D
design rudder torque, total, see D
Testing
100
200
300
400
Stemframes
Rudder nozzles
A 300 Docwnentation
Steering gears
Sea trials
301
A. General
A 100 Scope
101 Units equipped with their own propulsion machinery
are to be fitted with approved arrangements for main and
auxiliary steering. Main and auxiliary steering arrangements
may consist of steering nozzles, ordinary rudders, thrusters
or only ordinary propellers, or a combination of same.
102 The requirements in. this Section are applicable to
steering arrangement involving steering nozzles. Other arrangements will be specially considered.
The following plans are to be submitted for approval:
- stemframe, outline of the propeller
- rudder including details of bearings, pintles and rudder
lock arrangement
- rudder stock including details of couplings, bolts and
keys
- rudder carrier
- steering appliances including details of torque transmitting parts (tiller, rotor, vanes, piston rods, etc.), foundation bolts and chocks, rudder stoppers
- piping diagram according to Pt. 4 Ch. I
- electrical wiring diagram according to Pt.4 Ch.4
- remote control diagram according to Pt.4 Ch.5.
The plans are to give full details of scantlings and arrangement as well as data necessary for verifying scantling cal-
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 10 - Pt.3 Ch.2 Sec.4
culations. Material specifications and particulars about heat
treatment are also required.
302 For important components of welded construction
(e.g. tiller), full details of the joints, welding procedure,
filler metal and heat treatment after welding are to be specified on the plans.
303 Plans of the following items are to be submitted for
information:
-
general arrangement drawing
overload protections
rudder angle indicator
locking or brake arrangement.
-
pintles
rudder structural parts
rudder stock
tiller or rotor
crosshead
cylinders/rams
rotorhousing
manifolds
hydraulic pipes with design pressure
> 50 bar.
402 •Works certificate• will be accepted for:
-
bolts and pins
stoppers
steering gear covers
steering gear pistons.
B. Materials
B 100 Plates and sections
101 Selection of material grades for plates and sections is
to be based on material thickness. NV-steel grades as given
in Pt.3 Ch.l Sec.2 for secondary structure application (0°C)
will normally be accepted.
102 In cases where transmission of tensile stresses
through! the thickness cannot be avoided, the adoption of
structural steel with improved through thickness properties
may be required.
103 The material factor f 1 included in the various formulae
for plate structures may be taken as given in Pt.3 Ch. I Sec.2
for primary structure category.
B 200 Forgings and castings
201 Materials with minimum specified tensile strength
lower than 400 N/mm2 or higher than 900 N/mm2 will normally not be accepted in rudder stocks or pintles, keys and
bolts.
Nodular cast iron may be accepted in certain parts after
special considerations.
202 The material factor fl for furgings (including rolled
B 500 Heat treatment
501 All forgings and castings used for the stem frame and
rudder structure, including rudder stock etc. are to be heat
treated as specified in Pt.2 Ch.I Sec.6 and 8 respectively.
Fabricated parts in the steering gear are to be fully annealed
after welding.
C. Arrangement and Details
C 100 Sternframes and rudders
101 Rudder arrangements are assumed to be of the nozzle
type, the propeller being arranged within the nozzle, see
Fig. 1. Other arrangements will be specially considered.
102 Suitable arrangement to prevent the rudder from lifting is to be provided.
103 A stuffing box of approved type is to be fitted to prevent water from entering the steering gear compartment and
the lubricant from being washed away from the rudder carrier.
round bars) and castings may be taken as:
a
f1 = (
u
a
dso
2:~)
RUDDER CARRIE
UPPER BEARING
RUDDER STOCK
NECK BEARING
(WITH 5TUFFING BOX)
minimum upper yield stress in N/mm2,. not to be
taken greater than 70 % of the ultimate tensile
strength
= 0,75 for Gf > 240
= 1,0 for Gf< 240
HORIZONTAL FLANGE
COUPLING
-
I
------r--
B 300 Bearing materials
301 Bearing materials for bushings are to be stainless steel,
bronze, white metal, or synthetic material. Stainless steel or
bronze bushings are to be used in an approved combination
with steel or bronze liners on the pintle or stock.
The difference in hardness of bushing and liners is not to
be less than 65 Brinell. 13 % Cromium steel is to be avoided.
302 Synthetic bearing materials are to be of an approved
type. The Rockwell hardness is not to be less than 80
N/mm2 measured at 23°C and with 50% moisture.
B 400 Certificates
401 •Det Norske Veritas' certificate• will be required for:
1
FIN
I
I
I
I
I
t
I 1·',I
I
I
I. I
/~j_[T
~~T" .-'~
:I 1·:I
I
\,I
HEEL PINTLE
SOLE P
Fig. I
Steering nozzle
- stemframe structural parts
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.4 - Page 11
C 200
201
Steering gear
For arrangement and details of steering gear, see H.
>--- I
D. Design Loads and Stress Analysis
D 100 Rudder force
"0
101 The design rudder force for ordinary steering nozzles
is given by:
FR= 0,09 (D + 2b) D V
2
w
§
<.!)
z
(kN)
I
I
'- -r1..,' .L I
I
I
FR= 0,35 b D V
2
I
i
,
I
z
I
0
I ,I
= length of nozzle, in m
maximum speed in transit, in knots, minimum 7
knots. For astern condition, the speed will be specially considered.
The rudder force need not be taken larger than:
\
,.....-1\b·
~-r
0
w
_,
= mean diameter of nozzle, in m, see Fig. 2
\
+--~-
<l
D
b
V
\
I
z
u:
,.
""'_,
uJ
Xtt
"
b
(kN)
0/3 Qfl
b/3
102 If a vertical fin is fitted at the aft end of the nozzle,
the design rudder force given in 101 is to be increased by:
FF= 0,05 (D + 2a) D V
D
a
V
2
FORWARD
(kN)
ASTERN
= as given in 101
= breadth of fin, in m
= as given in 101
2
(kN)
The rudder torque from nozzles with a fin fitted at the aft
end may be specially considered when the unit is going astern.
D 300
D 200
Rudder torques
201
The design rudder torque for steering nozzles is to be
taken as:
x0 ,
b
Xfr
=
=
=
=
longitudinal distance in m from the centreline of the
rudder stock to the centre of FR
0,33 b-xrr, minimum 0, l b for ahead condition
0,66 bv-xrr for astern condition
as given in 101
projected longitudinal distance in m from the centreline of the rudder stock to the leading edge.
See also Fig. 2.
202 If a vertical fin is fitted at the aft end of the nozzle,
the corresponding rudder torque caused by the fin is to be
taken as:
MTF =FF Xef
Xef
Xff
= 0,33 a-Xff for ahead condition
= as given in 102
longitudinal distance in m from the centreline of the
rudder stock to the leading edge of the fin, but as the
leading edge is aft of the centreline of the rudder
stock, the value is to be taken negative.
See also Fig. 2.
203
Mrr = MTR+ MTF
301 The scantlings of stemframe, rudder, rudder stock,
steering gear and bearings may be based on direct stress
analysis. The design loads are to comply with the rudder
force and rudder torque given in 100 and 200. Allowable
stresses are indicated for the various members in E-H.
E. Sternframes
E 100 General
101 Stem frames are to be of simple design, and sudden
changes of section are to be avoided. Where shell plating,
floors or other structural parts are welded to the sternframe,
there is to be a gradual thickness reduction towards the joint.
102 The plates of welded propeller posts may be welded
to a suitable steel bar at the after end of the propeller post.
104 Stresses determined by direct calculations as indicated
in D 300 are normally not to exceed the following values:
- Normal stress: u = 80 f1 (N/mm2)
- Shear stress: T = 50 f1 (N/mm2)
E 200
The total rudder torque is:
(kNm)
Stress analysis
103 Stemframes are to be effectively connected to the
surrounding hull structures. In particular the stem bearing
is to be connected to the transom floor adjacent to the rudder
stock.
(kNm)
= 0,66 a-Xff for astern condition
a
Xe-VALUES
FIN
Fig. 2
xe and xr values etc.
This part of the total rudder force need not be taken larger
than:
FF= 0,2a D V
FORWARD}
NOZZLE}
ASTERN
Propeller posts
201 The boss thickness at the bore for the stem tube is not
to be less than:
DEf NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 12 -
Pt.3 Ch.2 Sec.4
t= 5
dp
.,j~-60
(mm)
Z1
Z2 = - 3
3
(cm)
= rule diameter of propeller shaft in mm.
Z1 = as given in 302.
202 The scantlings of fabricated propeller posts are not to
be less than given in Table El. Where the section adopted
differs from the specified prototypes, the section modulus
about the longitudinal axis is not to be less than the minimum given.
F. Rudder Nozzles
F 100
E 300
Sole pieces
301 The sole piece is to extend at least two frame spaces
forward of forward edge of the propeller boss. The cross
section of this extended part may be gradually reduced to the
cross section necessary for an efficient connection to the pla
te keel.
302 The section modulus requirement of the sole piece
about a vertical axis abaft the forward edge of the propeller
post is given by:
Z1 =
l,
6,25 (FR+ Fp) I,
fl
101 The following requirements for construction of nozzles may be applied to fixed and steering nozzles of diameter
4 metres or less.
Nozzles with greater diameter will be specially considered.
102 The nozzle may be supplied with a vertical doubleplated steering fin, fitted at the aft end of the nozzle.
103 Stresses determined by direct calculations as indicated
in D 300 are normally not to exceed the following values:
- Normal stress: " = 110 fl (N /mm2)
- Shear stress: 7 = 50 fl (N/mm2)
3
(cm )
= distance in m from the centre line of the rudder stock
to the section in question. l is not to be taken less
than half the free length of the sole piece
104 Means for draining the nozzle and fin completely is
to be provided. Drain plugs are to be fitted with efficient
packing.
105 Internal surfaces are to be covered by a corrosion-resistant coating after pressure-testing and possible stress-relieving.
Table El Propeller post
Welded
General
Cast
106 Before fmal mounting of pintles, the contact between
conical surfaces of pintles and their housings is to be
checked by marking with Prussian blue or by similar
method. When mounting the pintles, care is to be taken to
ensure that packings will not obstruct the contact between
mating surfaces. The pintle and its nut are to be so secured
that they cannot move relatively to each other.
Type of
propeller
post
F 200
201
Nozzle and rudder fin plating
The thickness of the nozzle shell is not to be less than:
Values in mm:
Length, I
t=
Thickness, t1
3
ka
Fi
2,4
L
Fi
Minimum
section
modulus, Z
1,35
f1
3,7
L
s
Fi
Values in cm :
1,3L
L
L l)
P
f1
be included.
=
=
b
1) When calculating the sectio?:Wodulus, adjoining shell plates
within a width equal to 53.yL from the after end of the post may
L
IC
In
kasyP
(mm), minimum 7 mm
-vf1
Breadth, b
Thickness, t2
5,8
length of the vessel, defined as the greatest fore and aft dimension in m, measured along the centreline or a projection
on the centreline.
303 The section modulus of the sole piece about a horizontal axis abaft the forward edge of the propeller post is in
no place to be less than:
=
=
=
(1,1 - 0,25 s/b)2
maximum 1,0 for s/b = 0,4
minimum 0,72 for slb = 1,0
the smaller of the distances between the longitudinal
or the transverse/vertical web plates in m
the larger of the distances between the longitudinal
or the transverse/vertical web plates in m
pressure impulse from propeller in kN /m2, min. 10
kN/m2
Po in zone I, in way of propeller
0,5 Po in zone II
0,33 Po in zone III.
If Po is unknown, Po may be taken 80 kN/m2. For extension of zones, see Fig. 3.
202 Leading and trailing edges are to be made by bars or
tubes of suitable thickness.
203 The thickness requirement to side, top and bottom
plating of a vertical fin is to be as given in 201, zone III.
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.4 - Page 13
F 500
b
1:)13
Welding
501 Welding of nozzles is to be carried out in accordance
with Ch.I Sec.8.
Slot welding is to be limited as far as possible.
The length of slots is not to be less than the distance between
the slots.
Zonem
502 The inner shell plate of nozzle is to be welded to the
internal structure with double continuous welds.
Zone I
Propellerj
Zone JI
Zone II
503 The outer shell plate may be slot welded to the internal
structure, the extension depending on the web spacing s:
s > 300 mm = the outer plating is to be welded continuously
to at least one web. For the rest slot welds
may be accepted
s ~ 300 mm = all connections may be slot welded.
I
__
--1---
i:.;._~-
G. Rudder Stocks and Pintles
Fig. 3
Nozzle section, pressure zones
G 100
F 300 Web plates
301 The thickness of internal structures of nozzles as well
as fins is not to be less than the shell plating in zone III.
302 The web shear area of nozzle and fin is to be specially
considered in way of supports.
F 400
Section modulus
401 The section modulus of a nozzle section about a longitudinal axis is not to be less than
2 2
Z =kb D V
k
1,0 for rudder nozzles
b
V
= 0,75 for fixed nozzles
= as given in D 101
= as given in D 101.
General
101 Stresses determined by direct calculations as indicated
in D 3 00 are normall~ to give equivalent stress se not exceeding llO f1 N/mm .
The equivalent stress for elements in combined bending and
torsion may be taken as:
"e = .J~~-2_+_3_T2-
= bending stress in N/mm2
"
torsional stress in N/mm2
=
T
102 The requirements to diameters are applicable regardless of liner. Both ahead and astern conditions are to be
considered.
3
(cm )
G 200
201
Rudder stock with couplings
The diameter requirement is given by:
An actual nozzle section as shown in Fig. 4 may be substituted by a rectangular section with height h and flange
breadths 0,4 b, as indicated.
402 For vertical fins, the section modulus requirement for
the cross-section in question is given by_:
z
(N/mm2)
(mm)
kb
I above the rudder carrier
l,14FpD
f1
[I
+
~
l
6
2
( :;; )
]
at arbitrary cross-section
Ma = calculated bending moment in kNm at the section in
question.
I
202 If direct calculations of bending moment distribution
are not carried out, Ma may be taken as follows:
b .
FRD
At the neck bearing Ma= - (kNm)
6
At the upper bearing Ma = 0
Between the upper bearing and the neck bearing Ma may
be varied linearly.
D
203 Where the rudder stock is connected to the rudder by
horizontal flange coupling the following requirements are to
be complied with:
Fig. 4
Section modulus of nozzle sections
-
DET
The diameter of coupling bolts measured at bottom of
threads is not to be less than:
NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 14 - Pt.3 Ch.2 Sec.4
db= 0,62
d,
n
=
e
=
=
=
(mm)
Rule diameter of rudder stock at coupling flange
in mm as given in 201
number of coupling bolts, at least 6 coupling bolts
are to be used
mean distance in mm from the centreline of bolts
to the centreline of the bolt system
material factor (f1) for rudder stock
material factor (f1) for bolts.
- The meao distance from the centre of the coupling to the
bolts is not to be less than 0,9 d,
- If the coupling is subjected to bending stresses, the mean
distance from the centreline of the bolts to the longitudinal centreline of the coupling is not to be less than 0,6
d
- The width of material outside the bolt holes is not to be
less thao 0,67 dh
- The thickness ot coupling flanges is not to be less than
0,9 db
- Nuts are to secured by split pins or other efficient means.
Fig. 5
Cone coupling
G 300 Bearings
301 The bearing surface area is not to be less than:
hb d,1 =
i:.:,
6
10
2
(mm )
401
hb = effective height in mm of bearing surface
dsi
diameter in mm of rudder stock or pintie measured
on the outside of liners, if fitted
P = calculated reaction force in kN at the bearing in
question (see also 304)
Pm = as given in 302.
302
G 400 Pintles
The maximum surface pressure Pm for the various
bearing combinations is to be taken as:
The diameter of pintles is not to be less than:
~ = 10
P
fF
fi
(mm)
= as given in 301
402 Pintles are to have a conical connection to the gudgeons. See Fig. 5, cone coupling.
The taper on the diameter is to comply with:
Pm = 7000 kN/m2 for steel against stainless steel or bronze
Pm = 4500 kN/m2 for steel against white metal, oil lubriPm
cated
5500 kN /m2 for steel against synthetic materials,
water lubricated.
Th~ height of bearing surfaces is not to be taken
greater thiln:
303
hb :S: 1,2 d,1
(mm)
d,1 = as given in 301.
304 If direct calculations of reaction forces are not carried
out, P at various bearings may be taken as:
P = 0, 7 FR (kN) at neck bearing
The length of pintle housing,
pintle diameter.
It, is not to be less than the rule
403
The dimensions at the nut are not to be less than (see
Fig. 5):
- Thread diameter, external:
d = 0,65 d,,
- ifeight of nut:
hn = 0,6 dg
- Outer diameter of nut:
dn = 1,2 cl, or dn = 1,5 dg, whichever is the greater.
The nut is to be sufficiently secured.
404 If the pintle is connected to the gudgeon by a nut
P = 0,6 FR (kN) at heel pintle bearing
P = 0, 1 FR (kN) at upper bearing
which is mounted and dismounted using hydraulic apparatus, the case will be specially considered.
305 The bearing clearance on diameter is normally not to
405 The width of material outside the hole for the bushing
is not to be less thao 25 % of the pintle diameter.
be less thao:
0,001 d,1 + 1,0 (mm) when metal bearing material
0,002 d,1 + 1,0 (mm) when synthetic bearing material
406 The thickness of any bushings in rudder bearings is
not to be less thao:
ly = 0,32
d,1 = as given in 301
Due attention should, however, be given to the manufacturer's recommended clearance. For· pressure lubricated bearings the clearaoce will be specially considered.
P
.JP (mm),
min. 8 mm
= as given in 301.
The bushing is to be effectively secured to the bearing.
DET NORSKE VERITAS
Rules for Mobile Offshore Units, July 1995
Pt.3 Ch.2 Sec.4 - Page 15
110 A means of communication is to be provided between
the bridge and the steering gear compartment.
H. Steering Gears
H 100
General
H 200
101 Steering appliances are to be mounted on substantial
seatings, which will effectively transmit the rudder torque to
the hull structnre. Deck plating under rudder carrier is to
be of substantial thickness. Prior to installation all welding
near the seatings have to be completed. The deck underneath is to be efficiently supported to take the weight of
steering gear and rudder with rudder stock.
102 Electrical power units are to be placed on elevated
platforms in order to avoid water splash.
103 Suitable stopping arrangements are to be provided for
the rudder. The stoppers may be an integral part of the
rudder actuator. Power cut-out to the actuator is to operate
at a smaller angle of helm than those for the rudder.
104 An efficient locking or brake arrangement is to be
fitted to keep the rudder steady during change-over from
normal to auxiliary steering or when otherwise necessary.
Steering appliances not provided with redundancy in power
units and power supply in accordance with 107 are to be
provided with means for centring of the rudder in case of a
single failure in a power unit or in its associated control
system or loss of power.
Steering capacity
201 The requirements to steering capacity stated below
refer to rudders with normal angle of helm. Other capacities
may be accepted upon special consideration in each case.
Full power is not to give turning moments resulting in
damage to rudder structure, rudder stock or bearings in case
of sticking rudder due to grounding or other external effects.
202 The steering appliances intended for main steering are
to be capable of turning the rudder over from 35 degrees
on one side to 35 degrees on the other side with the unit
running ahead at maximum continuous speed. The rudder
is to be capable of being tnrned from 35 degrees on either
side to 30 degrees on the other side in not more than 28
seconds under the conditions mentioned.
203 The steering appliances intended for auxiliary steering
are to be capable of tnrning the rudder over from 15 degrees
on one side to 15 degrees on the other side in not more than
60 seconds with the unit running at a speed of 7 knots, or
at full speed if this is lower.
H 300
Power supply
to be arranged to protect the actuator against impact or ex-
301 The steering appliances intended to main steering are
to comprise one or more power units when the rudder stock
diameter exceeds 120 mm or when necessary to fulfil the
requirements in 102.
cessive load on the rudder.
Torque or force transmitting parts not protected from overloading are to have dimensions giving equivalent strength to
that of rudder head or stock.
302 The steering appliances intended to auxiliary steering
are to comprise one or more power units when the rudder
stock diameter exceeds 230 mm or when necessary to fulfil
the requirements in 103.
106 Remote steering from the bridge and steering power
units are to be provided with redundancy. Mutnal independence between duplicated components or sub-systems
will be required as far as reasonable and practicable.
Auxiliary steering is to be possible shortly after discovery
of a single failure in any redundant part and with capacity
to steer the unit at navigable speed.
Steering wheel or lever· shaft may be common for two parallel systems.
Indicators are to show systems ready for operation.
303 Power supply systems mentioned in 301 and 302 are
to be provided with redundancy, i.e. two power units are to
be mutually independent (e.g. separate supply from main
switchboard to each of two electrical units or one electrical
and the other diesel-hydraulic or compressed air hydraulic
operated). The requirement applies also to pilot or amplification systems.
Electric power supply is to be arranged in accordance with
Pt.4 Ch.4 Sec.3.
The time lag involved in restoring the lost power is not to
be more than 30 seconds.
107 Redundancy in the remote steering system or the
power units for a single rudder actuator is not required for:
Guidance note:
Electric power supply to one of the power units inclusive its
associated remote control system and rudder angle indicator is
advised to be arranged from emergency source of power.
105
Relief valves, slip couplings or equivalent devices are
- units fitted with two rudders, each with its own steering
appliances and capable of steering the unit with any one
rudder out of operation
- units fitted with two or more propellers capable of steering the unit with any one rudder out of operation and
provided with approved remote control from the bridge
- units fitted with one or more thruster(s) capable of steering the unit with any one rudder out of operation and
provided with approved remote control from the bridge.
108 Means are to be provided in the steering gear compartment to disconnect the remote steering systems from the
power circuits, and direct manual control of regulating devices (e.g. servo-valves) is to be arranged.
109 The angular position of the rudder is to be indicated
in the steering gear compartment and on the bridge. The
rudder angle indicating system is to be independent of any
automatic or feed-back control systems.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-c---
304 Hydraulic power supply for steering gears is not to
be arranged for other purposes. Supply lines from more than
one master pressure pump are to be duplicated with separate
isolating valves fitted directly on the actnator or manifold.
For general requirements, see Pt.4 Ch. I.
Guidance note:
Pilot operated blocking valves are preferably to be connected in
series with the isolating valves.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
305 When steering arrangement is in accordance with 107,
redundant power supply is not required.
H 400
Actuator housing, rudder carrier
401 The actnator housing may be cast or welded construction. Parts subjected to internal pressure are to satisfy
the requirements in Pt.4 Ch. I and Ch. 3 to the extent these
requirements are applicable.
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 16 -
Pt.3 Ch.2 Sec.4
The structural design is to be chosen with due respect
402
to transmission of reaction forces to the seatings.
403 The rudder carrier, or in case of an integral unit, the
rudder actuator and its fastening to foundations, is to be able
to take reaction forces due to bending set up in rudder stock.
Side chocks may be required in addition to fitted bolts.
H 500
Tiller arms, rotor vanes, etc,
501 The combined stresses due to bending and tension
(compression) set up in arms or vanes are to be less than
50 % of the lower yield strength of the material. Fillets are
to have smooth and rounded surfaces giving reasonable low
stress concentration.
502
The shearing force in each of the arms or vanes may
be expressed as:
p[7
The bending moment at the foot of arms or vanes may be
VP/cose~P0
expressed as:
MA= PA
(z- ~)
(kNm)
The sectional area of arms or vanes is, however, not to be
less than:
·
3
dso
AA= 5000 In
n
2
(mm)
=
length of tiller arm measured from centre of rudder
=
stock to point of action of driving force in m
number of arms or vanes (not to be taken greater than
3)
d = diameter in m of tiller boss
d, 0 = diameter in mm of rudder stock at tiller.
The value of I will depend on the design of the tiller or rotor
and also on the angle of helm as illustrated in Fig. 6.
H 600
Tiller boss
601 The ratio between the outer and inner diameter (mean
values) of the boss is not to be less than:
~
"\,/ I, 8
h
+ 1( without keyway )
and
Cd,;
"\,/ 2
h
h
+ 1( with keyway)
height of tiller boss in mm. h is not to be less than
0,75 d, 0 •
602 Splitted boss may normally be accepted and have to
be joined by at least four bolts and additionally be secured
by a key.
603 Assembly boss/rudder stock may be accepted without
key. The calculated friction torque is not to be less than
2 Mi.(µ= 0,17).
The maximum equivalent uni-axial stress
t1
is not to exceed
Fig. 6
Steering gears
95 % of the yield point or the 0,2 % proof stress of the material in the boss.
DET NORSKE VERITAS
Rules for Mobile Offshore Units, July 1995
Pt.3 Ch.2 Sec.4 - Page 17
H 700 Remote control system
701
2
2
Po= 10 Tru (kN/m ) min. 50 kN/m
Electric remote control sy_stems are to be arranged in accordance with Pt.4 Ch.4 Sec.3 G400. Failures like broken
line, loss of power etc. are not to impair the preset position
of the rudder until back-up system is m operation.
702 Control arrangement necessary to perform
+:follow-up~ steering may be common for two or more power
unil,, provided alternative steering will be possible after
failure in such device (e.g. direct manual control of the
pump unit).
H 800 Monitoring
801 For monitoring for electrical steering gear motors, see
Pt.4 Ch.4.
802 The following failures are to activate alarm:
Failure
Power supply to:
- power unit
- steering system
Low level in common system tank
Remarks
Exception,
see
Pt.4 Ch.4
TTH = transit
I 100 Sternframes
101 Built stemframes with closed sections are to be pres-
in m, maximum.
Upon special agreement with the Society the hydraulic test
may be replaced by an air tightness test in compliance with
Ch. I Sec.10 B.
I. 300
Steering gears
301
Housings with covers, cylinders and manifolds are to
be subjected to a hydrostatic pressure test.
The test pressure is to be according to Pt.4 Ch.I and Ch.3.
302
Main tiller/rotor, cast or welded, is to be non-destructive tested if found necessary.
303
On double rudder installation where the two units are
synchronized by means of a mechanical mechanism, mutual
adjustment is to be tested.
304 For survey and testing of hydraulic and electrical
parts, see Pt.4 Ch. I and Ch.4.
I
I. Testing
draug~t
400
Sea trials
401 A steering test is to be carried out during sea trials to
demonstrate that the functional and capacity requirements
are fulfilled.
sure tested on completion.
I
200 Rudder nozzles
201 Rudder nozzles are to be hydraulically tested with an
internal pressure:
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 18 - Pt.3 Ch.2 Sec.5
SECTION 5
MOORING AND TOWING EQUIPMENT
Contents
and towing equipment for mobile offshore units given by the
authorities for the territory in question.
A. General
A JOO Scope
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
D. Anchors
102 Column-stabilized units are to have an arrangement
for temporary and emergency mooring. Self-elevating units
are not required to have temporary or emergency mooring.
However, if a mooring system is installed, it will normally
be subject to classification. This will be stated in the Appendix to the Class Certificate. For units with the class notation POSMOOR or DYNPOS the system for position
keeping on location may in some situations cover the requirements for temporary and/or emergency mooring, see
104-105.
D 100
D 200
D 300
D 400
D 500
103 If the temporary or emergency mooring is a part of the
system for position keeping on location, the complete
mooring equipment is subjected to approval and certification
in accordance with 300.
A 200
A 300
Definitions
Documentation
B. Structural Arrangement for Mooring Equipment
B 100 General
C. Equipment Specification
C 100
C 200
D 600
General
Equipment number
General
Materials
Anchor shackle
Proof testing of anchor strength
Additional requirements for H.H.P. («High Holding
Power,.) anchors
Identification
E. Mooring Chain and Accessorie)
General
E 100
E 200
E 300
E 400
E 500
E 600
E 700
E 800
E 900
Materials
Heat treatment and mechanical testing of chain and accessories
Loading test
Proof load test
Dimensions and tolerances
Non-destructive testing (NDT)
Repair
Identification and documentation
105 For units with the class notation DYNPOS the Rule
requirements for emergency and temporary mooring in this
Section are to be complied with.
106 All units are to have an arrangement and devices for
towing as outlined in H.
A 200 Definitions
201 Temporary mooring in the Rule context is a mooring
system which is supposed to be used in sheltered waters or
harbour, and which is capable of keeping the unit from uncontrolled drift when exposed to moderate environmental
loads.
F. Steel Wire Ropes
F 100
F 200
F 300
104 For units with the class notation POSMOOR the requirements for emergency and temporary mooring in this
Section are normally covered by the additional class.
However, documentation is required, see 300.
General
Materials
Testing of steel wire ropes
G. Windlass and Chain Stoppers
202 Emergency mooring in the Rule context is a mooring
G 100
G 200
G 300
system which is supposed to be used in bad weather condition during transit movements of the unit and which is capable of keeping the vessel from uncontrolled drift when
exposed to environmental loads.
General design
Materials
Testing
Fairleads
H.
H
H
H
100
200
300
I.
1
I
1
Wire End Attachments
100 General
200 Material
300 Strength
203 Redundancy is the ability of a component or system
to maintain or restore its function when failure of one component has occurred.
General design
Materials
Strength and design load
A 300 Docmnentation
301 The following plans and particulars of the moonng
equipment are to be submitted for approval:
J. Arrangement and Devices for Towing
J
J
J
100
200
300
General
Material
Strength analysis
A. General
A 100 Scope
101 The requirements in this Section are applicable to the
equipment and installation for temporary mooring, emergency mooring and towing. Requirements to mooring systems for position keeping are given in Pt.6 Ch.2 (Additional
Class). For clarity the principles laid down in 102 to 106 are
also given in Table Al.
Guidance note:
Notice is to be payed to possible regulations concerning mooring
- equipment number calculations
- equipment system calculation including number of anchor
lines to be used during emergency and/or temporary
mooring, mass and type of anchors. Diameter, steel
grade and minimum breaking strength of stud link chain
cable and/ or diameter, construction and minimum break ing strength of steel wire rope, as applicable
- anchor and anchor shackle design/calculations if.not previously type approved as H.H.P. anchor. Material specification
- windlass/winch design. Material specifications for frame
work cable lifters, shafts and couplings
- chain stopper design. Material specification
- fairlead design. Material specification
- chain/wire connections if any. Type and design of wire
end attachment and end shackle if any. Material specification
- supporting structures
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.5 - Page 19
Table Al General view of mooring arrangement requirements
Type of
MOBILE OFFSHORE UNIT
MAIN CLASS Pt. 3 Ch. 2 Sec. 5
DURING 'TRANSIT CONDITION
TEMPORARY AND EMERGENCY
Mooring Equipment
SEMISUBMERSIBLE UNIT
Normally covered by:
POSMOOR
with class notation:
POSMOOR
COLUMNSTABILIZED
UNIT
(Documentation required)
SEMISUBMERSIBLE UNIT
with class notation:
Required
DYNPOS
SEMISUBMERSIBLE UNIT
ADDillONAL CLASS Pt.6
ON LOCATION
POSillON
Mooring Equipment
(see special rule requirement)
Covered by:
POSMOOR
Covered by:
DYNPOS
without additional class
Required
Not covered by:
The Classification
SUBMERSIBLE UNIT
Required
Covered by:
Resting on sea bottom
Not required
Covered by:
Legs resting on sea bed
without additional class
SELF-ELEVATING UNIT
- strength calculation of the windlass/winch (drum/cabefar,
shafts, couplings, frame work brakes, gear and part
wheel/chain stopper if relevant).
TableA2
Functional testing:
- H.H.P. anchor
D 500
- windlass/winch
- fairlead
G 300
304
For the items given in Table A2 Det Norske Veritas'
certification/inspection report will be required.
Strength testing:
-
anchor
anchor chain cable and accessories
steel, wire rope
parts of windlass/winch
D 400
E 400, 500
F 300
G 300
Material certificates:
- anchor
- anchor chain cable and accessories
(shackles, swivels etc.)
- steel wire rope (WC)
- windlass cable lifter
- winch drurri and drum flanges
- shafts for cable lifter and/or drum
- pawl wheel, stopper and couplings
- gear shafts and gear wheels (WC)
- windlass/winch framework (WC)
- brake components
- chain stopper
- fairlead (cable lifter/sheave,
shafts, housing and supports)
- wire end attachment (WC)
- shackles, flounder plate and chain
D 200
E 200, 300
F 200
G 200
G 200
G 200
G 200
G 200
G 200
G200
G 200
H 200
I 200
J 200
For items referred with CIVQ works' certificate from approved manufacturer will normally be accepted.
302 The following plans and particulars of the towing
equipment are to be submitted for approval:
-
fairleads and fastening devices for towlines. The plans
are to show clearly the supporting structure in way of the
fairleads and the fastening devices
- permanent towing equipment, such as chain cables, steel
wire ropes, shackles, rings, thimbles and flounder plate
- retrieving arrangement
- emergency arrangement.
-
calculation of the towing design load
strength calculation of the fairlead
B 100 General
101 For the purpose of temporary and emergency mooring
the unit is to be equipped with at least 2 of each of the fol-
lowing items:
- anchors
- chain cables
- chain lifters
- chain stoppers
- separate spaces in the chain lockers.
102 The anchors are to be effectively stowed and secured
in transit to prevent movement of anchor and chain due to
wave action. The arrangements are to provide an easy lead
·of the chain cable/wire rope from the windlass/winch to the
anchors. Upon release of the brake, the anchor is immediately to start falling by its own weight.
103 If anchors are supported directly by the shell, the shell
plating in way of the anchor stowage is to be increased in
thickness and the framing reinforced as necessary to ensure
an effective supporting of the anchor.
Anchors bolsters are to be efficiently supported to the main
structure.
104 The chain locker is to have adequate capacity and a
suitable form to provide a proper stowage of the chain cable,
and an easy direct lead for the cable into the chain pipes,
when the cable is fully stowed. The chain locker boundaries
and access openings are to be watertight. Provisions are to
303 The following plans and particulars are to be submitted for information:
- arrangement of the mooring equipment
- arrangement of the towing equipment
B. Structural Arrangement for Mooring Equipment
be made to minimize the probability of chain locker being
flooded in bad weather. Drainage facilities of the chain
locker are to be adopted.
Under normal operation of the mooring line provisions are
to be made for securing the inboard end. The arrangement
is to be such that the mooring line can be easily disconnected
in case of emergency.
105 Mooring systems with all-wire or chain/wire anchor
lines shall have provisions for securing the inboard ends of
the wire to the storage drum. This attachment is to be de-
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 20 -
Pt.3 Ch.2 Sec.5
signed in such a way that when including the frictional force
being applied through the turns of rope always to remain on
the drum it is able to withstand a force of not less than the
minimum wire rope breaking strength.
The fastening of the wire to the storage drum is to be made
in such a way that in case of emergency when the anchor
and chain/wire have to be sacrificed, the wire can be readily
made to slip from an accessible position. The storage drum
is to have adequate capacity to provide a proper stowage of
the wire.
106 Fairleads fitted between windlass/winch and anchor
are to be of the roller type.
107 The windlass/winch, chain stopper and fairlead are to
be efficiently supported to the main structure. The nominal
equivalent stress, Ge, in the supporting structures is nonnally
not to exceed 0,8 "f when subjected to a load equal to the
breaking strength of the unit's anchor line. The strength
analysis is to be made for the most unfavourable direction
of the anchor line, i.e. angle of attack to structure.
C. Equipment Specification
C 100 General
101 The equipment is in general to be in accordance with
the requirements given in Table Cl.
102 For self elevating units the requirements may alternatively be based on specified design conditions or design
strength of mooring lines, which are to be included in the
•Appendix to Classification Certificate•.
C 200
201
Equipment number
The equipment number is given by the formula:
EN
ti
A
=!i2 / 3 +A
moulded displacement in t in salt water (density
l ,025 tim3) on maximum transit draught.
= projected area in m2 of all the wind exposed surfaces
above the unit's light transit draught, in an upright
condition, taken as the projection of the unit in a
plane normal to the wind direction. The most unfavourable orientation relative to the wind is to be
used taking into account the arrangement of the
mooring system.
The shielding effect of members located behind each
other is normally not to be taken into account.
However, upon special consideration a reduced exposed area of the leeward members may be accepted. The shape of the wind exposed members is
normally not to be taken into account.
The solidification effect is normally not to be taken
into account.
=
202 To each group of equipment numbers, as they appear
in Table C 1, there is associated an equipment letter which
will be entered in the •Appendix to Classification
Certificate•. Additional letters may follow the equipment
letter, see D 104 and E 203. If the unit is equipped with
heavier equipment than required by the Rule, the letter
which corresponds to the lowermost satisfied group of
equipment numbers will replace the Rule requirement letter.
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.5 -
Page 21
Table Cl Equipment Table
Equipment
number
Exceeding not exceeding
720 - 780
780 - 840
840 - 910
910 - 980
980 -1 060
1 060 -1 140
1 140 -1 220
1 220 -1 300
1 300 -1 390
1 390 -1 480
1 480 -1 570
1 570 -1 670
1 670 -1 790
1 790 -1 930
1 930 -2 080
2 080 -2 230
2 230 -2 380
2 380 -2 530
2 530 -2 700
2 700 -2 870
2 870 -3 040
3 040 -3 210
3 210 -3 400
3 400 -3 600
3 600 -3 800
3 800 -4 000
4 000 -4 200
4 200 -4 400
4 400 -4 600
4 600 -4 800
4 800 -5 000
5 000 -5 200
5 200 -5 500
5 500 -5 800
5 800 -6 100
6 100 -6 500
6 500 -6 900
6 900 -7 400
7 400 -7 900
7 900 -8 400
8 400 -8 900
8 900 -9 400
9 400 -10 000
10 000 -10 700
10 700 -11 500
11 500 -12 400
12 400 -13 400
13 400 -14 600
14 600 -16 000
Stockless Anchors
Equipment
letter
Number
s
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
t
u
v
w
x
y
z
A
B
c
D
E
F
G
H
I
J
K
L
M
N
0
p
Q
R
s
T
u
v
w
x
y
z
A*
B*
C*
D*
E*
F*
G*
H*
I*
J*
K*
L*
M*
N*
O*
Mass per
anc/wr (kg)
2
2
2
2
3
3
280
460
640
850
060
300
Total
length (m)
Stud-link Chain Cables
Diameter and steel grade
NV K3 RIG (mm)
3 540
3 780
4 050
467,5
467,5
467,5
495
495
495
522,5
522,5
522,5
4 320
4 590
4 890
5 250
5 610
6 000
6 450
6 900
7 350
7 800
8 300
8 700
9 300
9 900
10 500
11 100
11 700
12 300
550
550
550
577,5
577,5
577,5
605
605
605
632,5
632,5
632,5
660
660
660
687,5
687,5
687,5
36
38
40
42
44
46
46
48
50
50
52
54
56
58
60
62
64
66
68
70
73
76
78
78
81
84
87
12 900
13 500
14 100
14 700
15 400
16100
16 900
17 800
18 800
20 000
21 500
23 000
24 500
26 000
27 500
29 000
31 000
33 000
35 500
38 500
42 000
46 000
715
715
715
742,5
742,5
742,5
742,5
742,5
742,5
770
770
770
770
770
770
770
770
770
770
770
770
770
87
90
92
95
97
97
100
102
107
111
114
117
122
127
132
132
137
142
147
152
157
162
NV K4 RIG (mm)
50
52
54
54
56
58
60
62
64
66
68
68
70
73
76
76
78
81
84
84
84
87
90
95
97
100
102
105
111
114
114
120
124
127
130
137
142
The mass of the head is not to be Jess than 60 % of the table
value.
D. Anchors
D 100 General
101 Anchor types dealt with are:
103 The mass of stocked anchor, the· stock not included,
is not to be Jess than 80 % of the table-value for ordinay
stockless anchors. The mass of the stock is to be 25 % of the
total mass of the anchor includmg the shackle, etc., but excluding the stock.
- ordinary stockless anchor
- ordinary stocked anchor
- H.H.P. (<High Holding Power>) anchor.
102 The mass of ordinary stock!ess anchors is not to be
less than given in C. The mass of individual anchors may
vary by ± 7 % of the table value, provided that the total mass
of anchors is not less than would have been required for
anchors of equal mass.
104 For anchors approved as H.H.P. anchors, the mass is
not to be less than 75 % of the requirements given in C. Jn
such cases the letter r will be added to the equipment letter.
105 The total mass of the anchors corresponding to a certain equipment number may be divided between 3 or 4 instead of 2 anchors. The mass of one anchor will then be 1/3
or 1/4 respectively of the total mass required.
DET NORSKE YERITAS
Rules for Mobile Offshore Units , July 1995
Page 22 -
Pt.3 Ch.2 Sec.5
106 If steel wire rope is accepted instead of stud link chain
cable, the mass of the anchors is to be at least 25 % in access
of the requirement given in Table Cl, see E 105.
D 200
Materials
201 Anchor heads and shanks may be cast, forged or fabricated from plate materials.
202 The materials are to comply with relevant specifications given in Pt.2. For cast steel, the requirements given for
general application, •Special quality», apply. For forged
and cast steel with tensile strength higher than 600 N/mm2,
specifications of chemical composition and mechanical properties are to be submitted for approval for the equipment
in question. Plate material in welded anchors is to be of the
grades as given in Table G3.
D 300
Anchor shackle
301 The anchor shackle body is to be made of forged or
cast steel and the shackle pin is to be made of forged or
rolled steel. Acceptance tests are to include charpy V-notch
impact test, and the results are to comply with the requirements specified for chain cable links of corresponding
strength level. In other respects the materials are to comply
with the relevant requirements given in Pt.2 Ch. I for forgings, respectively castings for general application, .:Special
quality•.
302 The diameter of the shackle leg is normally not to be
less than:
applied diameter of stud link chain with steel grade
equal to the shackle material, see Table C 1. If the
steel grade for the shackle differs from the chain,
d, has to be corrected correspondingly, see Table
El-E2. For shackle material with minimum tensile
strength different from that of the steel grades NV
K3 RIG and NV K4 RIG, linear interpolation between table values of d, will normally be accepted.
303 The diameter of the shackle pin is normally not to be
less than the greater of:
Mass of
Proof
anchor test load
kg
kN
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
3300
3400
3500
3600
3700
3800
3900
4000
4100
4200
4300
4400
4500
4600
4700
4800
4900
5000
5100
5200
5300
5400
5500
5600
376
388
401
414
427
438
450
462
474
484
495
506
517
528
537
547
557
567
577
586
595
604
613
622
631
638
645
653
661
669
677
685
691
699
706
Moss of
Proof
anchor test load
kg
kN
5700
5800
5900
6000
6100
6200
6300
6400
6500
6600
6700
6800
6900
7000
7200
7400
7600
7800
8000
8200
8400
8600
8800
9000
9200
9400
9600
9800
10000
10500
11000
11500
12000
12500
13000
713
721
728
735
740
747
754
760
767
773
779
786
795
804
818
832
845
861
877
892
908
922
936
949
961
975
987
999
1010
1040
1070
1090
1110
1130
1160
Mass of
Proof
anchor test load
kg
kN
13500
14000
14500
15000
15500
16000
16500
17000
17500
18000
18500
19000
19500
20000
21000
22000
23000
24000
25000
26000
27000
28000
29000
30000
31000
32000
34000
36000
38000
40000
42000
44000
46000
48000
1180
1210
1230
1260
1270
1300
1330
1360
1390
1410
1440
1470
1490
1520
1570
1620
1670
1720
1770
1800
1850
1900
1940
1990
2030
2070
2160
2250
2330
2410
2490
2570
2650
2730
403 The proof load is to be applied on the arm or on the
palm at a distance from the extremity of the bill equal to 1/3
of the distance between it and the centre of the crown. The
shackle is to be tested with the anchor.
404 For stockless anchors, both arms are to be tested simultaneously, first on one side of the shank and then on the
other side.
For stocked anchors, each arm is to be tested individually.
405 The anchors are to withstand the specified proof load
without showing signs of defects.
~=0,7~
= as given in 302
= free length of pin. It is assumed that materials of the
same tensile strength are used in shackle body and
pin. For different materials dp will be specially considered.
D 400
Table DI Proof test load for anchors
Proof testing of anchor strength
401 Ordinary anchors and H.H.P. anchors are to be subjected to proof testing in a machine specially approved for
this purpose.
402 The proof test is to be as given in Table DI, dependent on the mass of equivalent anchor, defined as follows:
- total mass of ordinary stockless anchors
- mass of ordinary stocked anchors excluding the stock
- 4/3 of the total mass of H.H.P. anchors
For intermediate values of mass the test load is to be determined by linear interpolation.
D 500 Additional requirements for H.H.P. (<.High
Holding Power,,) anchors
501 H.H.P. anchors are to be designed for effective hold
of the sea bed irrespective of the angle or position at which
they first settle on the sea bed after dropping from the anchor's stowage. In case of doubt a demonstration of these
abilities may be required.
502 The design approval of H.H.P. anchors is normally
given as a type approval, and the anchors are listed in the
•List of Approved Manufacturers and Type Approved Products, Hull Equipment>.
503 H.H.P. anchors for which approval is sought are to
be tested on sea bed to show that they have a holding power
per unit of mass at least twice that of an ordinary stock.less
anchor.
504 If approval is sought for a range of anchor sizes, at
least two sizes are to be tested. The mass of the larger anchor to be tested is not to be less than 1/10 of that of the
largest anchor for which approval is sought. The smaller of
the two anchors to be tested is to have a mass not less than
1/10 of that of the larger.
DET NORSKE VERITAS
Rules for Mobile Offshore Units, July 1995
Pt.3 Ch.2 Sec.5 -
505 Each test is to comprise a comparison between at least
two anchors, one ordinary stockless anchor and one H.H.P.
anchor. The mass of the anchors are to be as equal as possible.
506 The tests are to be conducted on at least 3 different
types of bottom, which normally are to be: soft mud or silt,
sand or gravel, and hard clay or similar compacted material.
507 The tests are normally to be carried out by means of
a tug. The pull is to be measured by dynamometer or determined from recently verified curves of the tug's bollard
pull as function of propeller r.p.m. Provided the pull is
measured by verified curves of the tug's bollard pull the
minimum water depth for the tests is to be 20 m.
The diameter of the chain cables connected to the anchors
is to be as required for the equipment letter in question.
During the test the length of the chain cable on each anchor
is to be sufficient to obtain an approximately horiwntal pull
on the anchor. Normally, a horizontal distance between anchor and tug equal to 10 times the water depth will be sufficient.
D 600
The total length of the anchor chain is to be at least 50%
respectively 100 % in excess of the requirement given in
Table Cl for the reduced diameter of the chain.
E 200
Materials
201 The chain links are to be made by electric resistance
welding (flash welding). Shackles and swivels may be cast
or forged from steel grades corresponding to the different
chain grades with respect to mechanical properties.
The studs in stud link chains are to be made of cast or forged
steel. Material must be suitable for heat treatment as applied
for the chain links.
202 The materials for mooring chain of grades NV K3
RIG and NV K4 RIG are to be delivered with Del Norske
Veritas' material certificate in compliance with the requirements given in Pt.2 Ch.! Sec.6.
203 Units equipped with chain grades NV K3 RIG and
NV K4 RIG will have the letters spec added to the equipment letter.
Table El Mechanic.al properties for chain and accessories
Identification
Test, parameter
601 The following marks are to be stamped on one side
of the anchor:
-
Page 23
NVK3
RIG
NVK4
RIG
Tensile test
mass of anchor (excluding possible stock)
H.H.P., when approved as high holding power anchor
certificate No.
date of test
Del Norske Veritas' stamp.
Yield stress REH or Rpo 2 N/mm2
Tensile strength RM
' N/mm2
Elongation As
%
Reduction of area Z % I)
Yield to tensile ratio, aim value 2)
Impact test (KV)
Impact energy, average value J 3)
Impact energy, single value J 4)
•c
Test temperature
E. Mooring Chain and Accessories
min.580
min.690 min.860
min.12
min.17
min.50
min.50
max.0,92 max.0,92
min.40
min.30
-15
min.40
min.30
-20
I) For cast accessories, this requirement will be specially considered
by the Society.
E 100 General
101 Mooring chain and accessories are to be made by
manufacturers approved by the Society for the pertinent type
of anchor chain, size and method of manufacture. Approval
and -production testing are to be carried out in accordance
with the Certification Note •Certification of Offshore
Mooring Chain», which can be obtained from the Society
upon request. The relevant requirements of Pt.2 Ch. I Sec. I
are also applicable. Chain grade NV K3 RIG and NV K4
RIG are the only applicable for temporary and permanent
mooring of Mobile Offshore Units unless otherwise agreed.
102 Manufacturers of NV K3 RIG and NV K4 RIG chain
and/or accessories shall have an approved Quality Assurance
system.
103 The design of chain links and accessories are subject
to approval and are to be in accordance with Fig. 1. Deviations in accordance with International Standard
IS0/1704-1973 will generally be accepted. Detailed drawings are to be submitted for approval.
104 The diameter and total length of stud link chain is not
to be less than given in Table Cl, Equipment Table.
105 Upon special consideration by the Society, the stud
link chain may be substituted by a steel wire rope and an
increased mass of anchor, provided suitable winches having
positive control of the steel wire rope at all times are also
fitted. The length and strength of the steel wire rope and the
mass of anchors are to be as given in F 103 and D 106.
106 If the total mass of anchors is divided between 3 or 4
instead of 2 anchors, the diameter of the anchor chain is to
be based on a mass corresponding to 1/3 respectively 1/4
of the total mass of the anchors required according to the
equipment number of the unit.
2)
Subject to agreement with the Society, this requirement may be
dispensed with. Detailed information is given in the Certification
Note No.2.6 «Certification of Offshore Mooring ChaiID-.
3) Min. average value 36 J for weld zone.
4) Min. single value 27 J for weld zone.
E 300 Heat treatment and mechanical testing of chain
and accessories
301 All chain and accessories for chain, regardless of manufacturing process, are to be heat treated in accordance
with approved specification. A description of the heat treatment process is to be given on the certificate.
302 Chain and accessories are to be subjected to mechanical testing in the heat treated condition. Mechanical testing
is to be carried out after the proof testing unless otherwise
agreed. Material for testiog of chain is obtained by supplying chain lengths with extra links that are securely attached
to the chain during the entire heat treatment. The extent of
testiog is to be one set of tests for every cast or 400 m of
chain length whichever comes first. Samples for mechanical
testiog are to be given an identification mark showing the
part of the chain length, heat treatment batch or cast which
they represent. The test set comprises;
one tensile test clear of the weld (opposite side to flash
weld)
- three Charpy V-notch impact tests with the notch clear
of the weld (opposite side to flash weld)
- three Charpy V-notch impact tests from the bend region
of the link I)
- three Charpy V-notch impact tests with the notch in the
middle of the flash weld
-
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 24 -
Pt.3 Ch.2 Sec.5
CONNECTION OF CABLE
TO ANCHOR
ENO SHACKLE
3.350
0
N
40
090 \.!ID
).750
9.70
1.40
0
0
~
0
0
N
~
"'
0
--r
0
--+-
4
,.;
'
!'>
-+--t-.
--,a +-
~I
~
6. ~.Q
8. 2 0
ENLARGED LINK
COMMON LINK
E.ND
LIN~
.
0
M
60
Fig. 1
Standard dimensions of stud link chain cable
1) Subject to agreement with the Society, this testing may be omitted provided the manufacturer by means of statistical data verifies that the impact requirements are consistantly met.
For forged and cast shackles, swivels etc. batch testing involving each heat treatment batch and each cast is to be applied in accordance with approved procedure. For chain as
well as for accessories the test results are to satisfy the requirements given in Table El.
E 400 Loading test
401 A loading test specimen for chain consists of at least
3 common links connected together. The links are to be
manufactured at the same time and in the same way as the
chain, heat treated, and non-destructive tested as the chain.
During the heat treatment the test specimen is to be securely
attached to the chain.
402 For the chain one loading test specimen is to be taken
from every cast or every 400 m of chain, whichever comes
first, and tested for the minimum load bearing capacity given
in Table E2 for the intended grade and size of chain.
403 The loading test specimens and the chain and accessories are to be given an identification mark showing the
part of chain length, heat treatment batch or cast which they
represent.
404 Chain accessories are to be tested for the minimum
load bearing capacity prescribed for the grade and size of
chain for which they are intended according to E 405. At
least one item out of every cast or every 100 items, which-
DET
ever comes first, is to be tested. For individually produced
accessories, alternative tests may be accepted after special
consideration.
Accessories which have been subjected to a loading test are
to be scrapped.
405 Each loading test specimen is to be tested at least to
the minimum load bearing capacity for a minimum of 30
sec. before unloading. The specimens will be considered to
have passed the test if no fracture has occurred after application of the prescribed load.
406 If the test fails, a thorough examination under supervision of the Surveyor shall be carried out in order to identify the cause of failure. In addition, two more specimens
shall be cut out from the chain length concerned and subjected to the specified load. If failure occurs, examinations
shall be carried out. Based on the results of failure investigations it will be decided whether parts of the chain length
may be accepted.
E 500 Proof load test
501 Each length of the chain is to be proof load tested in
a machine specially approved for that purpose, and is to
withstand at least the load given in Table EZ for the size and
grade of chain concerned. All joining shackles, end shackles
and swivels are to be tested with the proof load prescribed
for the chain concerned. Further details regarding proof load
testing are given in the Certification Note «Certification of
Offshore Mooring Chain>.
NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.5 -
TableE2 Requirements for proof loading and load testing
Chain of grade
NVK3 RIG
Diameter
of chain
mm
50
52
54
56
58
60
62
64
66
68
70
73
76
78
81
84
87
90
92
95
97
100
102
105
107
Ill
114
117
120
122
124
127
130
132
137
142
147
152
157
162
Minimum
proof
load
level
kN
Minimwn
lood
1480
1590
1710
1830
1960
2090
2220
2360
2500
2640
2780
3010
3240
3400
3640
3890
4150
4410
4590
4860
5040
5320
5510
5800
6000
6400
6700
7000
7320
7350
7750
8070
8390
8610
9170
9730
10290
10870
11450
12040
Chain of grade
NVK4RIG
Minimum
load
kN
Minimum
proof
load
level
kN
2110
2270
2440
2610
2790
2980
3170
3360
3560
3760
3970
4290
4620
4850
5190
5550
5920
6290
6540
6930
7200
7600
7870
8280
8560
9130
9570
10000
10450
10750
11060
11520
11980
12290
13090
13890
14700
15520
16350
17190
2160
2330
2500
2680
2860
3050
3240
3440
3640
3850
4060
4390
4730
4960
5320
5680
6060
6440
6700
7100
7370
7780
8050
8480
8760
9350
9790
10240
10700
11010
11320
11790
12270
12590
13400
14220
15050
15890
16740
17500
2740
2960
3170
3400
3630
3870
4120
4370
4630
4890
5160
5580
6010
6300
6750
7220
7690
8180
8510
9010
9360
9880
10230
10770
11130
11870
12440
13010
13590
13980
14380
14980
15580
15990
17020
18060
19120
20190
21270
22350
bearing
capacity
bearing
capacity
kN
Page 25
602 The allowable manufacturing tolerances on diameter
of finished chain links are given in Table E3.
The cross-sectional area of the link at the crown is not to
be less than the area represented by nominal diameter. The
calculation of the cross-sectional area is to be based on the
average of four measurements of the diameter equally
spaced around the circumference. 5 % of the links for every
length of chain are to be chosen randomly for measurements
of the diameter.
Table E3 Tolerances for diameter of finished chain links
Chain
Manufacturing
Local
Plus
dimension
tolerance I)
nominal
%
minus
tolerance 2)
minus
tolerance 3)
mm
mm
2
3
4
5
6
7
diameter de
mm
51-80
81-120
121-160
5
1) The weld region diameter tolerances are to be specially consid-
ered by the Society during approval.
2) The cross sectional area is to be at least the theoretical area for
the nominal diameter.
3) Max. allowable grinding depth.
603 The entire chain is to be checked for the length, five
links at a time. By the five link check the first five links shall
be measured. From the next set of five links, at least one
link from the previous five link set shall be included. This
procedure is to be followed for the entire chain length. The
allowable manufacturing tolerance on length of 5 links is-0
+ 2,5 %. The measurements are to be taken while the chain
is loaded to 5-10 % of the minimum proof load. The links
held in the end blocks may be excluded from this measurement.
604 The allowable manufacturing tolerance on other dimensions than described in 602 and 603, is ± 2,5 %. For
common links, 5 % of the links from every length of chain
is to be chosen randomly for measurements of outside length
and width, and all other dimensions according to approved
design drawings. Tolerances of offset, twist and angular
deviation of stud are given in Fig. 2.
502 The proof load testing shall be performed to give an
uniform stress distribution in the different links, e.g. by
horizontal support of the links tested or by testing in vertical
position. In cases where the existing equipment does not allow horizontal support of the chain during testing, the chain
shall be tested twice with 180° rotation around its axis.
503 If one link breaks during proof load testing, a thorough examination under supervision of the Surveyor shall
be carried out in order to identify the cause of failure. In
addition, two loading test specimens as described in E 401
are to be cut out, one on each side of the broken link, and
tested for the minimum load bearing capacity prescribed. If
failure occurs, examinations shall be carried out. Based on
the results of failure investigations it will be decided whether
parts of the chain length may be accepted.
Each failure during proof load testing shall be reported to
the Surveyor.
E 600
Dimensions and tolerances
601 All required measurements are to be taken after proof
load testing. The measurements are to be carried out to the
satisfaction of the Surveyor.
Stud position
Offset a
Angular deviation
Twist 'I'
G
Tolerance
O,lOD
±40
±50
Fig. 2
Tolerances for stud position
605 For chain accessories, one part out of 25 shall be
checked for dimensions according to approved drawings after proof load testing.
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 26 -
E 700
Pt.3 Ch.2 Sec.5
Non-destructive testing (NDT)
701 Subsequent to the proof load testing a careful visual
inspection of all chain links, and accessories is to be carried
out. In addition to visual examination two examination
techniques are to be performed:
- certificate No.
- Del Norske Veritas' stamp
- manufacturer's name or trade mark
The Certificate number may be exchanged against an abbreviation or equivalent. If so, this shall be stated in the
certificate.
- magnetic particle examination (MPE) for surface defects
- ultrasonic examination for internal defects, particularly in
the flash weld region of the chain links
902 Each connecting common link inserted according to
802 is to be marked on the stud as follows:
Acceptable procedures with respect to operator qualification,
calibration, acceptance criteria and extent of testing will be
found in the Certification Note •Certification of Offshore
Mooring Chain».
-
702 Chains and accessories shall be sand- or shot blasted
prior to performance of NDT to permit a thorough examination.
E 800
Repair
801 Shallow surface defects may be repaired by local
grinding. The grinding shall be done parallel to the longitudinal direction of the link, and the groove shall be well
rounded and forming a smooth transition to the surface. The
maximum grinding depth is given in Table E3. Repaired
areas shall be rechecked to verify complete removal of defects.
802 Links seriously damaged are to be replaced with joining shackles of approved type and grade, or with connecting
common links corresponding to the original ones as regards
grade and specified properties. The use of other material and
processes of manufacture will be subject to approval in each
case. Each connecting common link is to be subjected to a
satisfactory method of heat treatment (normalizing, normalizing and tempering or quenching and tempering) as required, without affecting adjacent links, if the entire chain
is not reheat treated. Processes for individual treatment of
connecting common links will be subject to special approval
by the Society. Approval will be considered on the basis of
appropriate and comprehensive tests of extra links manufactured and treated according to the processes applied. The
repaired chain length is finally to be subjected to the required proof load test unless otherwise agreed.
803 Defective accessories for mooring chain (shackles and
swivels) are to be replaced by new ones of the same grade
as the chain, or better.
804 Any other method for repair than those described in
801, 802 and 803 will be subject to approval by the Society
in each individual case.
805 Chain lengths shall not contain more than one detachable joining link per 150 m.
E 900
901
Identification and documentation
The chain shall be marked at the following places:
- at each end
- on connecting common links
- on links next to shackles or connecting common links.
All marked links shall be stated on the certificate, and the
marking shall make it possible to recognize leading and tail
end of the chain.
In addition to the above required marking, the first and last
common link of each individual charge used in the continuous length shall be adequately and traceably marked.
The marking shall be permanent and legible throughout the
expected lifetime of the chain.
The chain shall be marked on the studs as follows:
- chain grade according to Table El
chain grade according to Table El
certificate No.
Del N orske V eritas' stamp
replacement link No.
manufacturer's name or trade mark
The chain certificate shall contain information on number
and location of connecting links. The certificate number and
replacement link number may be exchanged against an abbreviation or equivalent. If so, this shall be stated in the
certificate.
903
-
Each shackle and swivel is to be marked as follows:
chain grade according to Table El
certificate No.
Del Norske Veritas' stamp
manufacturer's name or trade mark
identification No.
A shackle replacing a common link shall be stated in the
chain certificate with information on link number of replaced
link. The certificate nnmber may be exchanged against an
abbreviation or equivalent. If so, this shall be stated in the
certificate. The identification number shall be stamped on
each individual part of the shackle to enable a correct assembly.
904 A complete Chain Inspection and Testing Report in
booklet form shall be provided by the chain manufacturer
for each continuous chain length. This booklet shall include
all dimensional checks, test and inspection reports, NDT
reports, process records, photographs, etc., as well as any
non-conformity, corrective action and repair work. Each
Chain Certificate shall cover only one length of chain. All
accompanying documents, appendices and reports shall
carry reference to the original certificate number.
905 A complete inspection and testing report in booklet
form shall be provided by the manufacturer of chain accessories for each order. This booklet shall include all dimensional checks, test and inspection reports, process records,
photographs, NDT reports, etc., as well as any non-conformity, corrective action and repair work. Each type of
accessory shall be covered by separate certificates. All accompanying documents, appendices and reports shall carry
reference to the original certificate number.
906 The manufacturer will be responsible for storing, in a
safe and easy retrievable manner, all documentation produced for a period of at least 10 years.
F. Steel Wire Ropes
F 100
General
101 Steel wire ropes, are to be made by an approved manufacturer.
102 The strands of steel wire ropes are to be made in equal
lay construction (stranded in one operation), and are normally to be divided in groups as follows:
- 6xl9 Group consists of 6 strands with min. 16 and max
27 wires in each strand.
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.5 - Page 27
- 6x36 Group consists of 6 strands with min. 27 and max.
49 wires in each strand.
Fig. 3 gives examples of rope constructions. Other rope
constructions may be accepted by the Society upon special
consideration.
The fibre core is to be manufactured from a synthetic fibre.
203 Unless otherwise stated in the approved specification,
all wire ropes are to. be lubricated. The lubrications are to
have no injurious effect on the steel wires or on the fibres
in the rope.
F 300 Testing of steel wire ropes
301 Steel wire ropes are to be tested by pulling a portion
of the rope to destruction. The test length is to be taken as
30 times the rope diameter.
The breaking load of the ropes is not to be less than given
in Table Fl for the dimension concerned.
Table Fl Test loads and mass, Steel wire ropes
6
x
+
6x19+1WRC
Seale
19 1 FC
Filler
Construetion groups
mm
6 x 19
group
6 x 19
group
and
6 x 36
6x 16 + 1 Fe
Warrington Seale
6xl6+ IWRC
Warrington Seale
Rope with fibre core (FC)
Minimum required
breaking strength in kN
Norn.
dia.
group
24
26
28
30
32
36
40
44
48
52
56
60
1570
N/mm2
1770
N/mm 2
299
351
407
468
530
671
829
1000
1190
1400
1620
1860
337
396
459
527
598
757
934
1130
1350
1580
1830
2100
Approx.
mass
kg per
100 m
214
251
291
334
380
480
593
718
854
1000
1160
1330
Rope with independent wire-rope core (IWRC)
Norn.
Minimum required
Approx.
breaking strength in kN
dia.
mm
mass
1570
1770
kg per
N/mm 2
N/mm2
Construetion groups
6 x 19
FC
= Fibre core
group
lWRC = Independent wire
rope core
6x46+ IWRC
Warrington Seale
6 x 19
group
and
6 x 36
Fig. 3
Constructions of steel wire ropes
group
103 If steel wire rope is accepted instead of stud link chain
cable, the length of the steel wire rope is to be at least 50 %
in excess of the requirement given in Table C 1 for the chain
cables. The strength of the steel wire rope is not to be less
than 75 % of the minimum breaking strength required for the
substituted chain cable with the steel grade NV K3 RIG,
according to Table E2.
F 200
6 x36
group
Materials
201 Wire for steel wire ropes is to be made by open
hearth, electric furnace, LD process or by other processes
specially approved by the Society.
Normally, the tensile strength of the wires is to be 1570
N/mm2 or 1770 N/mm2. The wire is to be galvanized or
bright (uncoated). Galvanized wire is to comply with the
specifications in ISO Standard 2232.
202 The steel core is to be an independent wire rope.
Normally, the wires in a steel core are to be of similar tensile strength to that of the main strand, but are not to be less
than 1570 N/mm2.
24
26
28
30
32
36
40
44
48
52
56
60
64
68
72
76
80
84
88
92
96
100
104
108
112
116
120
124
128
323
379
440
505
573
725
895
1080
1290
1510
1750
2010
2290
2590
2900
3230
3580
3950
4330
4730
5160
5590
6050
6520
7020
7530
8060
8600
9170
364
428
496
569
646
817
1010
1220
1450
1710
1980
2270
2580
2920
3270
3640
4040
4450
4880
5340
5810
6310
6820
7360
7910
8490
9080
9700
10330
100 m
241
283
328
376
428
542
669
810
964
1130
1310
1510
1710
1930
2170
2420
2680
2950
3240
3540
3850
4180
4520
4880
5250
5630
6020
6430
6850
302 If facilities are not available for pulling the complete
cross section of the rope to destruction, the breaking load
may be determined by testing separately 10 % of all wires
from each strand. The breaking strength of the rope is then
considered to be:
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 28 - Pt.3 Ch.2 Sec.5
P=ftk
strength of the chain cable, without any permanent deformation of the stressed parts and without brake slip.
(kNn)
= average breaking strength of one wire in kN
= total number of wires
= lay factor as given in Table F2
f
t
k
107 Calculations indicating compliance with the requirements in 105 and 106 may be dispensed with when complete
shop test verification is to be carried out.
108 The chain stoppers and their attachments are to be
able to withstand the minimum breaking strength of the
chain cable, without any permanent deformation of the
stressed parts. The chain stoppers are to be so designed that
additional bending of the individual link does not occur and
the links are evenly supported.
Table F2 Lay factor k
Rope construction
group
Rope with FC
Rope with lWRD
6x19
6x36
0,86
0,84
0,80
0,78
303
The following individual wire tests are to be performed:
- torsion test
- reverse bend test
- weight and uniformity of zink coating.
G 200
201
Windlass/winch components are to be made from
materials as stated in Table G2.
Table G2 Material requirements for windlasses/winches
These tests are to be made in accordance with and are to
comply with ISO Standard 2232.
G. Windlass and Chain Stoppers
G 100
Materials
Item
Material requirements
Cable lifter and pawl wheel:
Ordinary cast steel
Nodular cast iron 1)
Cable lifter shaft:
Forged or rolled steel
Driving shaft:
Forged or rolled steel
Gear wheels:
Forged or rolled steel
Cast steel
Nodular cast iron l)
Couplings:
Forged steel
Cast steel
Nodular cast iron I)
Wire drum, drum flanges:
Cast steel
Rolled steel
Nodular cast iron l)
General design
101 The anchors are normally to be operated by a specially designed windlass.
102 The windlass is to have one cable lifter for each
stowed anchor. The cable lifter is normally to be connected
to the driving shaft by release coupling and provided with
brake.
Drum shaft:
Forged or rolled steel
103
For each chain cable there is normally to be a chain
stopper device.
Stopper, pawl stopper with
shafts:
Forged or rolled steel
Cast steel
104 Electrically driven windlasses are to have a torque
limiting device. Electric motors are to comply with the requirements of Pt.4 Ch.4.
Brake components:
Forged or rolled steel
Cast steel
105 The windlass with prime mover is to be able to exert
the pull specified by Table Gl directly on the cable lifter.
For double windlasses the requirements apply to one side at
a time.
Table Gl Lifting power
Lifting force and speed
Normal lifting force for
30 min in N
Mean hoisting speed
Max. lift force for 2 min.
(no speed requirement)
d,.
l) To be considered in each case.
202 Windlasses and chain stoppers may be cast components or fabricated from plate materials. The material in the
cast components is to be cast steel or nodular cast iron with
elongation not less than 18 %. Plate material in welded parts
is to be of the grade as given in Table G3.
Grade of chain
NVK3RIG
NVK4RIG
46,6 d/
Table G3 Plate material grades
Thickness
inmm
Normal strength
structural steel
High strength
structural steel
ts; 20
20<tS25
25<tS40
40< tS 50 l)
A
AH
52,8 d, 2
9 m/min.
1,5 x normal
lifting force
= diameter of chain in mm.
G 300
106 The capacity of the windlass brake is to be sufficient
301
DET
AH
DH
EH
l) Larger thickness than 50 mm may be accepted upon special con-
Attention is to be paid to stress concentrations in keyways
and other stress raisers and also to dynamic effects due to
sudden starting or stopping of the prime mover or anchor
chain.
for safe stopping of anchor and chain cable when paying
out.
The windlass with brakes engaged and release coupling disengaged is to be able to withstand a static pull of 65 % of the
chain cable minimum breaking strength given in Table E2,
without any permanent deformation of the stressed parts and
without brake slip.
If a chain stopper is not fitted, the windlass is to be able to
withstand a static pull equal to the minimum breaking
B
D
E
sideration.
Testing
Before assembly the following parts are to be pressure
tested:
-
housings with covers for hydraulic motors and pumps
hydraulic pipes
valves and fittings
pressure vessels.
The tests are to be carried out in accordance with Pt.4 Ch. I
and Ch.3.
NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.5 - Page 29
302 After completion at least one prime mover of the
windlasses is to be shop tested with respect to required lifting and breaking forces. If calculations have not previously
been approved shop testing of the complete windlass is to
be carried out.
H 200
303 After installation of the windlass on board, an an-
201
choring test is to be carried out to demonstrate that the
windlass with brakes etc. function satisfactorily. The mean
speed on the chain cable when hoisting the anchor and cable
is not to be less than 9 m/rnin. and is to be measured over
two shots (55 m) of chain cable during the trial. The trial
should be commenced with 3 shots (82,5 m) of chain cable
fully submerged. Where the depth of water in trial areas is
inadequate, consideration will be given to acceptance of
equivalent simulated conditions.
106 F airleads for combined chain/wire anchor line will be
considered in each case.
Materials
Generally the material in the fairlead wheel is to be
of cast steel. The hardness of the material is normally to
compatible but not exceeding that of the chain or wire.
202 The selection of material grades for plates in the fairlead housing is to be based on the plate thickness and the
design temperature. The parts which are to be welded to the
column structure are to be considered as special structure.
See Ch. I Sec.2, Fig. 1.
203 The material in the fairlead shafts are normally to be
of forged or rolled steel. For steel where "f> 240 N/mm2
the material factor f 1 may be taken as:
H. Fairleads
0,75
f1 = (
H 100 General design
2:~
)
101 Fairleads are to be of the roller type.
102 Normally the chain cable is to be directly conveyed
from the lower fairlead to the cable lifter, without interruption of an upper fairlead. An upper fairlead may be accepted only upon special consideration, taking into account
the fairlead diameter, number of fairlead pockets and the
distance between fairlead and cable lifter.
103 The lower fairlead is normally to be provided with a
swivel arrangement. For a chain cable fairlead the number
of pockets is normally not to be less than 5. The pockets are
to be designed for the joining shackles with due attention to
dimensional tolerances. The groove width is not to exceed
1,65 times the diameter of the common link.
Other constructions provided with similar or better supporting for chain cable may be accepted upon special consideration.
H 300 Strength and design load
301
In the structural part of the fairlead the nominal
equivalent stress, ae, is normally not to exceed 0,9 O'f when
subjected to a load equal to the breaking strength of the anchor line. The strength analysis is to be made for the most
unfavourable direction of the anchor line. The horizontal
design working range (DWR) and the vertical design inlet
angle (DIA) normally to be considered in the strength analysis are shown in Fig. 5.
'\
i
\
104 Chain cable fairleads without pockets may be accepted
-
+
PB
·~
~
3:.
Cl
DIA
"
upon special consideration.
P,,
105 For a steel cable fairlead the ratio between pitch diameter of fairlead wheel and nominal wire rope diameter is
not to be less than 16. This applies to all sheaves including
combined wire rope/chain arrangement of a mooring system. The groove in fairlead wheel is normally to satisfy the
relations as indicated in Fig.4.
DWR rr0
h9
r9
dw
P
arc of support.
depth of fairlead groove.
radius of fairlead groove.
nominal wire diameter.
pitch diameter.
p
Operational working range + 20°
Fig. S
Horiwntal DWR and vertical DIA
120' .; y .; 150'
1,35 dw .; h 9 .; 1,75 dw
r9 = 0,525 dw
y
HOR.
PLANE
I. Wire End Attachments
I 100
General
101
The strength of end connections and connecting links
for combined chain/wire systems may not be inferior to the
strength of the anchor line.
16
102 Wire rope end attachments of the open or closed
speller socket type will be accepted, see Fig. 6. Other end
attachment types will be considered in each separate case.
Fig. 4
Wire fairlead diameter/groove
103 Fastening of the end attachments on the wire rope is
to be carried out according to recognized standards and by
persons who are licensed by the manufacturer.
-~
dw
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 30 - Pt.3 Ch.2 Sec.5
I 200 Material
201 The sockets are to be made from cast steel grade for
special requirements according to Pt.2 Ch.I Sec.8.
I 300 Strength
301 The strength is to be specially considered. Dimensions
according to recognized standards will normally be accepted.
- environmental loads on the unit in different towing conditions
- thrust provided by the unit's own propulsion machinery,
if fitted
- bollard pull of towing vessel(s) intended to be used
The vessel under tow is to be able to maintain position when
subjected to a specified seastate wind and current velocity,
without the force in the towing arrangement exceeding its
towing design load.
Guidance note:
Environmental drift forces for world wide towing may be calculated according to the following weather conditions:
-
sustained wind velocity: VJminlO = 20 m/s, see Ch.l Sec.4 B
current velocity: Ve= 1 m/s
significant wave height: Hs = 5 m
average wave zero-up-crossing period in s: 6 :5 Tz::; 9
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
302
The required towing force, Fr in kN is defined as the
difference between the environmental drift forces and the
vessel's own thrust capacity.
The towing design load, Fo, to be used in the strength
analysis is a function of the required towing force and given
by:
IDENTIRC4TION
OPEN
CLOSED
SPELTER
SPELT ER
SOCKET
SOCKET
Fo = fFT
f
Fig. 6
Wire rope spelter socket
(kNn)
= design load factor
= 2,2-0,0008 Fr.
Normally: 1200 kN:;; Fo:;; 1500 kN
J. Arrangement and Devices for Towing
J 100 General
101 The unit is to have a permanent arrangement for towing. Bridle(s) or pennants for towing are to have clear way
from the fastening devices to the fairlead.
There is to be an arrangement for retrieval of the unit's
towline in case the connection to the towing vessel should
break.
102 In addition to the permanent towing arrangement,
there is to be possibility of using an emergency arrangement
of equivalent strength. Application of the unit's mooring
arrangement may be considered for this purpose.
103 The design load for the towing arrangement will be
stated in the umt's -t<Appendix to Classification Certificate».
Guidance note:
It is advised that the towing design load for the unit's towing
fastening devices and their supporting structures is not to be
taken less than 1500 kN.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
303
The minimum breaking strength of the unit's
towline/chain cable, Ps, is not to be less than 3 times the
towing design load, Fo
304 The nominal equivalent stress, "• in the flounder plate
is normally not to exceed "f when subjected to a load equal
to the breaking strength of the vessel's towline, Ps. The
strength analysis is to be made for the most unfavourable
direction of the towline.
305
J 200 Material
201 Plate materials in towline fastening devices and their
supporting structures are to be as given m Table G3.
202 Towlines of steel wire rope are to be in accordance
with the requirements given in F 200 and F 300.
J 300 Strength analysis
301 With the evaluation of the design load for the towing
arrangement the following matters are to be taken into consideration:
Towing fastening devices and their supporting structures are to be designed for a load equal to the minimum
breaking strength of the vessel's towline/chain cable, Ps.
Strength analysis are to be made for the most unfavourable
direction of the towline, i.e. angle of attack to
device/structure. The nominal equivalent stress, ae. in the
towing devices and their supporting structures is not to exceed 0,9 O"f and 0,8 O"f respectively.
306 All eyes in towing arrangement connections are to be
fitted with hard thimbles.
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.6 - Page 31
SECTION 6
STABILITY
Contents
ingly. This will be stated in the Appendix to
Classification Certificate.
A. <;,,neral
A 100 Scope
A 200
A 300
A 400
107 The requirements of Sec.7 are to be complied with,
as applicable.
Defmitions
Documentation for approval
Documentation for information
108 The requirements of this Chapter is based on the IMO
MODU Code 1989. Text which has been taken directly from
the Code is written in Italics.
B. Assumptions and Criteria
B
B
B
B
B
B
B
B
B
100
200
300
400
500
600
Righting moment and heeling moment cuives
Intact stability criteria
Damage stability - self-elevating units
Damage stability - column-stabilized units
Damage stability - all types of units
Extent of damage
700
Chain lockers
the
A 200 Definitions
201 The defmitions given hereunder apply to this Section
of the Rules only.
202
800
900
Load line and draught marks
Extent of watertight/weathertight closing of external
openings
B 1000 Internal watertight intergrity and subdivision
B 1100 Maximum allowable VCG-curves, column-stabilized un-
Mobile Offshore Units:
- column-stabilized units (Semi-submersibles)
- self-elevating units (Jack-ups)
Guidance note:
B 1200 Maximum allowable VCG-curves, self-elevating units
Regarding stability requirements for surface units with ship- or
barge-type displacement hull, reference is made to DNV Rules
B 1300 Inclining test and lightweight
for Ships.
its
B 1400 Loading conditions, column-stabilized units
--e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
B 1500 Stability manual or the stability part of the Operation
Manuals
B 1600 Stability requirements for heavy lift operations
203
Service modes:
- operation condition, i.e. normal working condition
- temporary conditions, i.e. transient conditions during
change of draught to reach another service mode
- survival condition, i.e. in case of severe storms
- transit condition.
A. General
A 100 Scope
101 The rules of this section deal with the following design
parameters of mobile offshore units:
1) hydrostatic particulars
2) wind exposed portions
3) draught range at various modes of service
4) extent of watertight/weathertight closing of external
openings
5) internal watertight integrity /subdivision
6) lightweight and loading conditions.
102 The combination of the design parameters under 101
(1-5) will determine the maximum allowable vertical centre
of gravity (VCG) of the unit at various service draughts and
modes.
103 The loading of the unit at various service draughts and
modes is to be within the limits of maximum allowable
VCG-curves described in Bl 100.
104 In order to determine VCG of the actual loading conditions, the lightweight and its centre of gravity must be
known. This is to be obtained by an inclining test to be
carried out in accordance with Bl200.
105 Preliminary stability approval, i.e. before completion,
will be based on estimated lightweight data and design
drawings. Final stability approval, i.e. after completion,
will be based on lightweight data obtained from the inclining
test, and ..cAs built» drawings.
106 Any alterations in iteI!lS mentioned in 101 during the
service of the unit are to be submitted to the Society for approval, and the stability manual is to be updated accord-
204 Maximum allowable vertical centre of gravity is the
maximum vertical centre of gravity which complies with
both intact and damage stability requirements given in this
Section, at a given draught and service mode. All loading
conditions are to have a vertical centre of gravity (VCG)
below the maximum allowable value for the given draught
and service mode. The free surface effect of each slack tank
should be calculated about the axis at which the moment of
inertia is the greatest, as the worst case.
205 Field move is the transit voyage which can be completed within 12 hours (transit time) or within the limits of
favourable reliable weather forecasts, whichever is less.
However, fo:i; certain operating areas and seasons, a field
move may exceed 12 hours if justified by independent reliable evidence.
Guidance note:
Weather may be considered favourable up to Beaufort condition
6, i.e. average wind speed of 24 knots.)
·---e-n-d--o-f-··-G-u-i-d-a-n-c-e---n-o-t-e---
206 Lightweight is the unvariable weight of the unit; i.e.
the basis for calculating the loading conditions. Anchors
and cables are to be excluded from the lightweight and included in the loading conditions as variable loads.
207 Variable load is the load that varies with the operation
of the unit such as deck cargo, fuel, lubricating oil, ballast
water, fresh water, feedwater in tanks, consumable stores
and crew and their effects.
208 Exposed portions are those portions of the columns,
pontoons and bracings which are located outboard of a line
drawn throngh the centres of the periphery columns. See
Fig. I.
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 32 - Pt.3 Ch.2 Sec.6
- maximum allowable VCG curves versus draught (for
intact criteria). See Bl!OO.
5) Damage stability calculations (see B!OO, B300, B400 and
B500):
- damage assumptions
- most critical damage cases (flooded volumes and moments)
- righting lever curves and tables versus heeling angle
in damage condition using maximum allowable VCG
at various draughts, including maximum draught
- wind heeling lever curves and tables versus heeling
angle corresponding to righting arm curves (wind velocity 50 knots)
- maximum allowable VCG curves versus draught (for
damage criteria). See Bl!OO.
do • OPERATING ORAUGHT
Dr = TRANSIT DRAUGHT
302
Fig.1
External watertight integrity plan (Freeboard Plan)
showing external openings with their means of closure and
Exposed portions
relevant details to comply with B800, B900 and Sec. 7 B301.
209 Damage penetration wne is defined as 1,5 m from the
outer skin. For column-stabilized units, the damage pene-
303 Internal watertight integrity plan (see B 1000) showing
watertight boundaries and internal openings (doors, hatches)
with their means of closure, as well as ducts, pipes and
tration zone is limited to exposed portions only.
210 First intercept is the angle of heel where the righting
moment curve intercepts the heeling moment curve for the
first time. The first intercept is also known as the •static
angle of he eh.
valves at pipe/duct penetration within the damage penetration zone. A list of watertight doors and hatches in watertight bulkheads and decks is to be attached. The list is to
include the following information:
-
ing moment curve intercepts the heeling moment curve for
the second time.
type of opening or penetration (kept closed at sea, normally closed at sea, frequently used at sea). See Sec.7
-
position of opening
dimensions of opening
212 Dynamic angle is the angle of heel where the area requirement according to B201 (under the righting and heeling
- detailed description of closing appliance
- measures to avoid progressive flooding (for penetration)
- details of any remote control and signals.
211
Second intercept is the angle of heel where the right-
moment curves) is achieved.
with respect to strength, and requirement for minimum air-
A list of non-watertight openings (for penetration of pipes,
cables etc.) on bulkheads and decks assumed watertight is
to be attached, if applicable.
gap according to Pt.3 Ch.2 Sec.2 B.
304
214 DownfWoding means any flooding of the interior of
any part of the buoyant structure of a unit through openings
which cannot be closed watertight, as appropriate, in order
to meet the intact or damage stability criteria, or which are
required for operational reason to be left open.
1) location, time and environmental conditions during test
2) communication facilities
215 Surface unit is a unit with a ship- or barge-type displacement hull of single or multiple bull construction intended for operation in the floating condition.
5) measurement of sea water density
A 300 Documentation for approval
7) foreign weights
*
The following documentation is to be submitted for approval:
8) missing weights
*
213 Safe draught is a draught which can be accepted under
loading condition d) as defined in Pt.3 Ch. I Sec.4 A301
301
Stability analysis is to include:
3) lightweight, deadweight and draft during test
*
*
4) procedure for measurement of draughts
6) liquids in tanks and sounding method
9) inclining weights
*
10) weight shifting sequence
1) Reference to rules requirements/criteria to be complied
with.
2) Hydrostatic model showing external boundaries and volumes assumed buoyant in the calculations.
3) Hydrostatic particulars of the whole model. See 306 1).
4) Intact stability calculations (see B!OO and B200):
-
Inclining test procedure is to include:
righting lever curves and tables versus heeling angle
for the draught range and various inclining axes using
maximum VCG values
- wind heeling lever curves and tables versus heeling
angle corresponding to those of the righting arm (wind
velocity 70 knots at transit and operation condition
and 100 knots at survival condition)
11) inclination measurement/pendulum arrangement
12) inclining moment and angles
*
* means anticipated values.
305 Inclining test report is to include all recorded data in
accordance with the accepted inclining test procedure. In
addition the following is to be included in the report:
-
corrections made for change in displacement and VCG
during test, if any; e.g. fuel consumed
-
moment diagram (inclining moment versus tangent heel-
ing angle)
- calculation of metacentric height GM
- calculation of lightweight and position of centre of gravity.
DET NORSKE VERITAS
.... -,
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.6 - Page 33
306 Stability manual, or the stability part of the operating
manuals is to include:
I) Limitations/exemptions related to the unit's stability, if
any.
2) Lightweight, as approved in the inclining test report, see
Bl200.
3) Hydrostatic particulars for the draught range (displacement, centre of buoyancy, waterplane area, centroid and
moment of inertia, position of metacentre above base
line, trimming and heeling unit moments, and tonnes per
cm immersion). All centres and moments of inertia
mentioned above are normally to be given in relation to
the unit's two main axes in the horizontal plane.
4) Tank capacity plan with data on capacity of each tank, its
centre of gravity and free surface effect.
5) List and plans (approved copy of documents specified in
302 and 303 above) of external and internal openings
with their closing appliances with instructions on how
and when they are to be closed.
maximum VCG's. The righting moment curves and wind
heeling moment curves are to be related to the most critical
axis.
102 Minimum standard of closing of openings leading to
spaces which are assumed buoyant, for the purpose of
achieving the necessary area under the GZ-curve, is to be
as follows (see also Fig.2 and 3):
-
When immersed before equilibrium position (first intercept) taking into account the effect of wind: Watertight
closed.
When immersed beyond equilibrium position up to the
dynamic angle: Weathertight closed.
103 The curves of wind heeling moments should be drawn
for wind forces calculated by the following formula:
2
F=0,5C,ChPV A
where:
F
=
the wind force (Newton)
6) Maximum allowable VCG-curves and ballasting/ deballasting curves to reach survival condition, when applicable. See BllOO.
C,
7) Loading conditions. See B1300.
ch
=
8) Notes to the Master on stability, loading of the unit,
changing of service modes, emergency procedures in
case of damage or storm and guidance on how to estimate
ice and snow weight as a function of thickness. In addition, a guidance on how to take account of marine growth
in tropical waters, when applicable.
the height coefficient depending on the height above
sea level of the structural member exposed to wind
(see Table B2)
P
=
the air mass density (1,222 kglm3)
V
=
the wind velocity (metres per second)
9) Example on routine checking of stability and blank forms
for this purpose.
10) General arrangement drawing showing main dimensions
etc.
11) A record of all changes to machinery, structure, outfitting and equipment that affect the light ship data should
be taken into account in daily operations.
A 400 Documentation for information
401 The following documentation is to be submitted for
information:
1) General Arrangement plan(s) and profile(s).
2) Lines plan and offset tables.
3) Tank capacity plan (showing capacity, geometry, centres
of gravity and free surface effect of each tank).
4) Other information relevant to the stability approval.
B. Assumptions and Criteria
B 100 Righting moment and heeling moment curves
Righting moment and wind heeling moment curves are to
be submitted as described in 101-106.
the shape coefficient depending on the shape of the
structural member exposed to the wind (see Table
Bl)
A
the projected area of all exposed sulfaces in either
the upright or the heeled condition (square metres)
104 Wind forces should be considered from any direction
relative to the unit and the value of the wind velocity should
be as follows:
- Jn general a minimum wind velocity of 36 mis (70 knots)
for offshore service should be used for normal operating
conditions and a minimum wind velocity of 51,5 mis (JOO
knots) should be used for the severe storm conditions.
·- l¥here a unit is to be limited in operation to sheltered
locations (protected inland waters such as lakes, bays,
swamps, rivers, etc.) consideration should be given to a
reduced wind velocity of not less than 25,8 mis (50 knots)
for normal operating conditions.
105 Jn calculating the projected areas to the vertical
plane, the area of sulfaces exposed to wind due to heel or
trim, such as under-deck sulfaces, etc., should be included
using the appropriate shape factor. Open truss work may
be approximated by taking 30% of the projected block area
of both the front and back section, i.e. 60% of the projected
area of one side.
106 Jn calculating the wind heeling moments, the lever of
the wind overturning force should be taken vertically from
the centre of pressure of all sulfaces exposed to the wind to
the centre of lateral resistance of the underwater body of the
unit. The unit is to be assumed floating free of mooring restraint.
101 Curves of righting moments and wind heeling moments similar to Fig.2 and Fig.3 with supporting calculations are to be prepared for the chosen draughts and
DET NORSKE VERITAS
Rules for Mobile Offshore Units, July 1995
Page 34 -
Pt.3 Ch.2 Sec.6
Table Bl Values of the coefficient C.
Righting moment
Shape
c.
Spherical
Cylindrical
0,4
0,5
Large flat surface (hull, deckhouse,
smooth under-deck areas)
1,0
Drilling derrick
1,25
Wires
Exposed beams and girders under deck
1,2
1,3
Small parts
Isolated shapes (crane, beam, etc.)
1,4
1,5
Clustered deckhouses or similar structures
1, 1
Table B2 Values of the coefficient Ch
Height above sea level (metres)
0 - 15,3
15,3 - 30,5
30,5 - 46,0
ch
1,00
1,10
Downflooding
angle
Angle Of inclinabon
Fig. 2
Righting moment and heeling moment curves
4) For column-stabilized units, the metacentric height is to
be at least 1,0 m in all operation, survival and transit
conditions. The metacentric height is not to be less than
0,3 min all temporary conditions.
1,20
46,0 - 61,0
1,30
61,0 - 76,0
76,0 - 91,5
1,37
91,5 - 106,5
1,48
106,5 - 122,0
1,52
122,0 - 137,0
137,0 - 152,5
1,56
1,43
152,5 - 167,5
1,60
1,63
167,5 - 183,0
1,67
183,0 - 198,0
198,0 - 213,5
1,70
1,72
213,5 - 228,5
1,75
228,5 - 244,0
244,0 - 256,0
1,77
above 256
Heeling
moment
1,79
1,80
107 The wind heeling moments are to be calculated for a
sufficient number of heel angles to define the curve.
108 Wind heeling moments derived from wind tunnel tests
on a representative model of the unit will be considered as
an alternative to the requested calculations of 103. Such
heeling moment determination is to include lift and drag at
various applicable heel angles.
B 200 Intact stability criteria
201
The stability of a unit in each mode of operation
should meet thefoUowing criteria (see also Fig.2):
J) For self-elevating units, the area under the righting moment curve to the second intercept, or downflooding angle, whichever is less, should not be less than 40% in
excess of the area under the wind heeling moment curve
to the same limiting angle.
202 Each unit should be capable of attaining a severe
storm condition in a period of time consistent with the meteorological conditions. The procedures recommended and
the approximate length of time required, considering both
operating conditions and transit conditions, should be contained in the stability manual. It should be possible to
achieve the severe storm condition without the removal or
relocation of solid consumables or other variable load.
However, the Society may permit loading a unit past the
point at which solid consumables would have to be removed
or relocated to go to severe storm condition under the following conditions, provided the allowable KG requirement
is not exceeded:
1) in a geographic location where weather conditions annually or seasonally do not become sufficiently severe to
require a unit to go to severe storm condition, or
2) where a unit is required to support extra deck load for a
short period of time that falls well within a period for
which the weather forecast is favourable.
The geographic locations, weather conditions and loading
conditions in which this is permitted should be identified in
the stability manual.
203 Alternative stability criteria may be considered by the
Society, provided an equivalent level of safety is maintained
and if they are demonstrated to afford adequate positive initial stability. Jn determining the acceptability of such criteria, the following will be considered and taken into account
as appropriate:
1) environmental conditions representing realistic winds
(including gusts) and waves appropriate for world-wide
service in various modes of operation;
2) dynamic response of a unit. Analysis should include the
results of wind tunnel tests, wave tank model tests, and
non-linear simulation, where appropriate. Any wind and
wave spectra used should cover sufficient frequency
ranges to ensure that critical motion responses are obtained;
2) For column-stabilized units the area under the righting
moment curve to the angle of downflooding should be not
less than 30% in excess of the area under the wind heeling moment curve to the same limiting angle.
3) potential for flooding taking into account dynamic re-
3) The righting moment curve should be positive over the
4) susceptibility to capsizing considering the unit's restora-
entire range of angles from upright to the second intercept.
sponses in a seaway;
tion energy and the static inclination due to the mean
wind speed and the maximum dynamic response;
5) an adequate safety margin to account for uncertainties.
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.6 -
Extentot
wc111t1ertJsht
integnty
402 The unit should provide sufficient buoyancy and stability in any operating or transit condition to withstand the
flooding of any watertight compartment wholly or partially
be/,ow the waterline in question, which is a pump-room, a
room containing machinery with a salt water cooling system
or a compartment adjacent to the sea, taking the following
considerations into account:
J
/
Page 35
RighLing mm'l'lent
Wind. treelk'lg moment
1) the angle of inclination after flooding should not be
greater than 25 °;
)
""
1---~7"---j----+-"'--'"---t--"'<-First Intercept
Angle of
indinatian
2) any opening below the final waterline should be made
watertight;
3) a range of positive stability should be provided, beyond
the calculated angle of inclination in these conditions, of
at least 7°.
Second Intercept
•• ,. ;ii 2
B 500 Damage stability - all types of units
501 Compliance with the requirements of 300 to 400
Fig. 3
Righting moment and wind heeling moment curves.
B 300 Damage stability - self-elevating units
301
The unit should have sufficient freeboard and be subdivided by means of watertight decks and bulkheads to provide sufficient buoyancy and stability to withstand in general
the flooding of any compartment in any operating or transit
condition consistent with the damage assumptions set out in
B601.
302
The unit should have sufficient reserve stability in a
damaged condition to with stand the wind heeling moment
based on a wind velocity of 25,8 mis (50 knots) superimposed from any direction. The area under the righting lever
curv@ should be at least equal to the area under the wind
heeling lever curve to an angle not exceeding either the angle of downflooding or the second intercept of the curves,
whichever is lesser. Both areas should be calculated from the
static angle of heel without wind.
303 The angle of inclination after the damage set out in
should be determined by calculations which take into consideration the proportions and design characteristics of the
unit and the arrangements and configuration of the damaged
compartments. In making these calculations it should be assumed that the unit is in the worst anticipated service condition as regards stability and is floating free of mooring
restraints.
502
The ability to reduce angles of inclination by pumping
out or ballasting compartments or application of mooring
forces, etc., should not be considered as justifying any relaxation of the requirements.
503 Alternative subdivision and damage stability criteria
may be considered for approval by the Society provided an
equivalent level of safety is maintained. In determining the
acceptability of such criteria, the Society should consider
at least the folwwing and take into account:
I} extent of damage as set out in 600;
B601 should not be greater than 17°.
2) on column-stabilized units, the flooding of any compartment as set out in 402;
304 Any opening below the final waterline through which
3) the provision of an adequate margin against capsizing
progressive flooding may occur, should be made watertight,
and openings within 4 m above the final waterline should
be made weathertight.
B 600
B 400 Damage stability - column-stabilized units
401 The unit should have sufficient freeboard and be subdivided by means of watertight decks and bulkheads to provide sufficient buoyancy and stability to withstand a wind
heeling moment induced by a wind vewcity of 25 ,8 mis (50
knots) superimposed from any direction in any operating or
transit condition, taking the following considerations into
account:
I} the angle of inclination after the damage set out in 602
should not be greater than 17°;
2) any opening through which progressive flooding may
occur beww the final waterline should be made watertight, and openings within 4 m above the final waterline
should be made weathertight;
3) the righting moment curve, after the damage set out
above, should have, from the first intercept to the lesser
of the extent of weathertight integrity required by 401 2)
and the second intercept, a range of at least 7°. Within
this range, the righting .moment curve should reach a
value of at least twice the wind heeling moment curve,
both being measured at the same angle. See Fig.3.
Extent of damage
601 Self-elevating units
In assessing the damage stability of self-elevating units the
following extent of damage should be assumed to occur between effective watertight bulkheads:
1) horizontal penetration: 1,5 m; and
2) vertical extent: from the base line upwards without limit.
3) The distance between effective watertight bulkheads or
their nearest stepped portions which are positioned within
the assumed extent of horiwntal penetration should be
not less than 3, 0 m; where there is a lesser distance one
or more of the adjacent bulkheads should be disregarded.
4) Where damage of a lesser extent than the above results
in a more severe condition, such lesser extent should be
assumed.
5) Where a mat is fitted the above extent of damage should
be applied to both the plaiform and the mat but not simultaneously, unless deemed necessary by the Society
due to their cwse proximity to each other.
6) All piping, ventilation systems, trunks, etc. within the extent of damage referred to in 601 should be assumed to
be damaged. Positive means of closure should be provided at watertight boundaries to preclude the progres-
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 36 -
Pt.3 Ch.2 Sec.6
sive jWoding of other spaces which are intended to be
intact.
602 Column-stabilized units
In assessing the damage stability of column-stabilized units,
the following extent of damage should be assumed:
I) Only those columns, underwater hulls and braces on the
periphery of the unit should be assumed to be damaged
and the damage should be assumed in the exposed portions of the columns, underwater hulls and braces.
2) Columns and braces should be assumed to be JWoded by
damage having a vertical extent of 3,0 m occurring at
any level between 5,0 m above and 3,0 m below the
draughts specified in the stability manual. Where a watertight flat is located within this region, the damage
shoul£l be assumed to have occurred in both compartments above and below the watertight flat in question.
Lesser distances above or below the draughts may be
applied to the satisfaction of the Society, taking into account the actual operating conditions. However, the required damage region should extend at least I ,5 m above
and below the draught specified in the stability manual.
3) The lateral or circumferential extent of damage should
be assumed to be 3 ,0 metres.
4) Horizantal penetration of damage should be assumed to
be 1,5 m.
5) Underwater hull or footings should be assumed to be
damaged when operating in a transit condition in the
same manner as indicated in I), 2), 3) and either 4) or
601 2), having regard to their shape.
6) All piping, ventilation systems, trunks, etc., within the
extent of damage should be assumed to be damaged.
Positive means of closure should be provided at watertight boundaries to preclude the progressive flooding of
other spaces which are intended to be intact.
603
Additional requirement for column-stabilized accommodation units: See Pt.5 Ch.2 Sec.2 E200.
803 Draught marks are to be located io positions which
will ensure accurate determioation of draughts, trim and heel
and where they are clearly visible to personnel operatiog the
unit. A surveyor of the Society is to ascertain that the marks
represent the correct distances to the lowermost part of the
unit, or to another well defined reference lioe. The reference
lioe is to be defioed io the stability manual.
804 Instruments for continuous draught sensing and reading are to be provided, if draught marks are not clearly visible for personnel operatiog the unit. It is to be possible to
take draught readiogs forward and aft on port and starboard
sides.
B 900 Extent of watertight/weathertight closing of
external openings
901 Watertight closing appliances are required for those
external openiogs being submerged at least up to an angle
of heel equal to the first iotercept io iotact or damage condition, whichever is greater.
902 Weathertight closiog appliances are required for those
external openiogs being submerged at least up to an angle
of heel equal to the dynamic angle. This applies to any
openiog within 4,0 m above the fioal waterlioe as well.
B 1000 Internal watertight intergrity and subdivision
1001 The iotemal subdivision is to be adequate to enable
the unit to comply with the damage stability requirements
of this Section.
1002 Ducts or pipiog which may cause progressive floodiog
in case of damage, will generally not be accepted in the
damage penetration zone.
B 1100 Maximum allowable VCG-curves,
column-stabilized units
1101 The following curves giviog the maximum allowable
vertical center of gravity ensuring compliance with both the
iotact stability criteria of 200 and the damage stability criteria of 300 and 400, with supportiog calculations, are to be
prepared:
Curve I:
(Operation
and transit
conditions)
B 700 Chain lockers
701 Chaio lockers which are not provided with weathertight closiog appliances, are to be provided with level alarm
or soundiog and bilge arrangement or draioage system in
accordance with Pt.4 Ch. I Sec.4. In this case the chain
pipes will be regarded as downfloodiog poiots.
Curve II:
(Survival
conditions)
702 When chaio lockers without weathertight closiog appliances are used as ballast tanks, downflooding through
chaio pipes can be disregarded at a given draught provided
that chaio lockers are:
Curve III:
(Temporary
conditions,
columnstabilized
units)
- equipped as ballast tanks accordiog to Pt.4 Ch. I Sec .4
and
Maximum VCG-values according to the intact stability criteria (with 70 knots wind)
and damage stability criteria with 50 knots
wind. The curve is at least to cover the operation and transit draughts.
Maximum VCG-values according to the intact stability criteria (with 100 knots wind).
The curve is at least to cover the range from
maximum operation draught to minimum
storm draught.
Maximum VCG-values according to the intact stability criteria (with 70 knots wind)
except that the minimum GM-requirement is
0,3 m. The curve is to cover the whole range
of draughts.
The curves are to be included in the stability manual.
- kept full at the given draught. This is to be stated io the
stability manual.
1102 In cases where a change io draught is necessary to
Conditions duriog the cleaniog of chaio lockers shall be
considered as temporary conditions.
reach the survival draught, ballasting/deballasting curves are
to be worked out and iocluded io the stability manual as
follows:
B 800 Load line and draught marks
801 The unit is to have load line marks accordiog to the
-
maximum permissible draught io the afloat condition.
802 The load line marks will be assigned on the basis of
compliance with the requirements· of this Section as well as
other applicable reqnirements.
Curve A: ballasting from transit draught to survival
draught.
- Curve B: deballasting from operatiog draught to survival
draught.
These curves are to be based on ballasted/deballasted water
at half the pontoon height (and possible transfer of mud).
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.6 -
Curves A and B are to be regarded as the final maximum
allowable VCG-curves for checking the actual loading conditions. The ballast curve A and B may be derived by taking
into account the actual changes in loading conditions
brought about by the change in the operating mode such as
change in mooring loads, removal of hook load, disconnection of marine riser etc., provided that such underlying
assumptions are clearly stated.
1103 The allowable VCG-curve is to reflect the lowest
VCG-values obtained for the most critical heeling axis at
each draught. The unit is to be assumed free to trim when
heeled.
B 1200 Maximum allowable VCG-curves, self-elevating
units
1201 For self-elevating units, it is normally only relevant to
draw curve I and curve II, as described in !100. Curve I
covers the field move conditions, while Curve II covers the
ocean tow conditions.
B 1300 Inclining test and lightweight
1301 An inclining test is required when the unit is as near
to completion as possible, to determine accurately the lightweight and position of centre of gravity. The test is to be
carried out in the presence of a surveyor to the Society.
1302 Before the test is arranged, a complete program is to
be submitted for acceptance. In particular the program is to
include information on draught, inclining weights, intended
heel, mooring, contents of liquid in tanks, weights missing,
and weights to go ashore. See A401.
1303 An inclining test is also required for successive units
of a design, even when they are sister units. However, for
sister self-elevating units, dispensation from the inclining
test may be considered. In case of such dispensation a satisfactory weight/displacement survey will be required. If the
result of the survey is not satisfactory, an inclining test is to
be performed .as described herein.
1304 Weights that are included in the lightweight during the
inclining test are to be specified in the inclining test report
and the stability manual. The lightweight data obtained from
the inclining test are also to be included.
Page 37
1404 When displacement and VCG are computed, the vertical component of the mooring forces and the weight of the
mooring lines onboard are to be included. Accurate data as
a function of the water depth are to be available in the stability manual.
1405 When operating in areas and seasons where ice and
snow accretion is probable, the weight of ice and snow is to
be included in the loading condition under 1407. Guidance
of how to estimate such weight and its centre of gravity is
to be included in the stability manual.
1406 It is to be shown, for each loading condition required
in 1407, which tanks are to be ballasted/deballasted (including possible transfer of mud) to bring the unit to even
keel at safe draught from equilibrium condition after damage
as specified in 600 (see also Pt.4 Ch. I Sec.4 C301).
1407 The following typical loading conditions are to be
calculated and shown in the stability manual:
-
normal operation condition at maximum draught taking
into account the maximum deck cargo and equipment in
the most unfavourable positions applicable
- survival condition at maximum survival draught assuming
the same weight distribution as in normal operating condition except for the necessary ballast adjustments and
possible transfer of liquid mud. Further, the marine riser
is to be assumed disconnected and a reasonable amount
of drill pipes is to be assumed stored in the derrick
- normal transit condition with related maximum deck
cargo (anchors on board)
- survival condition at maximum survival draught assuming
the same weight distribution as in normal transit condition except for the necessary ballast adjustments and
possible transfer of liquid mud.
B 1500 Stability manual or the stability part of the
Operation Manuals
1501 The information required under this section can either
be presented in a stability manual or be a part of the Operating Manuals. The stability manual is the final approval
document for a unit's stability, confirming compliance with
the requirements of this Section.
1305 The data for lightweight and centre of gravity is to be
continuously recorded and adjusted by the Master for any
items taken onboard or ashore after the inclining test. The
above will be stated in the Appendix to the Classification
Certificate.
1502 The stability manual is to include information in an
approved form, on the stability and watertight/weathertight
integrity of the unit as required under this Section. The stability information is to be presented in such a manner that
responsible personnel will be able to use it effectively under
varying operating conditions.
B 1400 Loading conditions, column-stabilized units
1503 An approved copy of the stability manual is to be kept
onboard.
1401 The VCG-values of all approved operating and transit
conditions, corrected for the effect of free surfaces, are to
be below the values given by Curve I, or, where applicable,
the ballasting curve giving the limiting VCG-values in order
to reach the survival draught as described in 1100.
1504 Information on any alterations introduced to the unit
which can alter the information included in the stability manual is to be submitted to the Society for approval. The stability manual is to be up-dated accordingly. This is to be
stated in the stability manual.
1402 The VCG-values of all temporary conditions, corrected for free surfaces, are to be below the values given by
Curve III as described in 1100.
B 1600 Stability requirements for heavy lift operations
1403 When the wind velocity exceeds 70 knots, the VCGvalues, corrected for the effect of free surfaces, are to be
below the values given by Curve II as described in 1100.
1601 Units, for which the lifting operation is the main, or
one of the main functions, are to be checked with respect to
stability requirements given in Pt.5 Ch.2 Sec.4 C200.
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 38 - Pt.3 Ch.2 Sec. 7
SECTION 7
WATERTIGHT INTEGRITY, FREEBOARD AND WEATHERTIGHT CLOSING
APPLIANCES
Contents
203 1974 SOLAS Convention means the International
Convention for the Safety of Life at Sea, 1974.
A. General
A 100
A 200
A 300
204 !UC 1966 means the International Convention on
Load Lines, 1966.
Application
Definitions
Documentation
205 Freeboard is the distance measured vertically downwards amidship from the upper edge of the deck line to the
upper edge in the related load line.
B. Watertight Int<grity
B JOO General
B
B
B
B
200
300
400
500
Internal openings
External openings
Strength of watertight doors and hatches
Operation and control of watertight doors and hatches
207 Damage waterline is the final equilibrium waterline
after a two-compartment damage as described in Sec.6.
C. Freeboard
C 100 General
C 200
C 300
Self-elevating units
Column-stabilized units
A 300
- deepest draught according to ILLC 1966 Certificate
- table of external openings and their closing appliances
giving the following information as applicable:
Weathertight hatches and coamings
Gaskets and closing devices
E. Ventilators and Air Pipes
E 100
1) type of closing appliance (watertight, weathertight, not
protected)
General
F. Inlets, Discharges and Scuppers
F 100
F 200
F 300
2) position of openings given by longitudinal, transverse
and vertical coordinates)
Sea inlets and discharges in closed systems
Discharges
3) vertical distance from lower edge of opening to the
most severe waterline (damage or intact, as applicable)
Scuppers
G. Side Scuttles and Windows
G 100 General
-
H. Testing of Doors and Hatches
H 100
H 200
H 300
Pressure testing of watertight doors and hatches
Hose testing of watertight and weathertight doors and
hatches
Function testing of watertight doors and hatches
A. General
A 100
Application
101 The rules in this section give requirements with regards to arrangement and design of watertight integrity and
freeboard.
102 Piping and electrical systems for operation of watertight closing appliances are to be in accordance with relevant
requirements given in Pt.4, Ch.! and Ch.5 unless otherwise
specified in this section.
103 Attention should be given to statutory requirements
of the National Authority having jurisdiction in the water
where the unit is located during operation.
A 200
Documentation
301 The builder is to submit a freeboard plan and the following documentation for approval. The freeboard plan is
to include information on the following:
D. Weathertight Closing Appliances
D 100 General
D 200 Weathertight doom
D 300
D 400
206 Position 1 and 2. In accordance with Regulation 13
of the International Convention on Load Line 1966 (ILLC
1966), adapted to Mobile Offshore Units.
Definitions
201 Weatertight means that in any sea conditions water
will not penetrate into the unit.
202 Watertight means capable of preventing the passage
of water through the structure under a head of water for
which the surrounding structure is designed.
-
the expected most severe waterlines are to be indicated
on the freeboard plan as a visual guidance
the parts of the structure that are included in the buoyancy
volumes
weathertight doors
side scuttles and windows
cargo hatchways
other hatches
ventilators
air pipes
openings in sides
scuppers and sanitary dischrages
sea inlets and outlets
freeing arrangement
structural design of watertight doors and hatches
lay out of watertight doors and hatches
schematic diagrams of local and remote control of watertight doors and hatches.
B. Watertight Integrity
B 100
General
101 The number of openings in watertight subdivisions is
to be kept to a minimum compatible with the design and
proper working of the unit. Where penetrations of watertight
decks and bulkheads are necessary for access, piping, ventilation, electrical cables etc., arrangements are to be made
to maintain the watertight integrity of the enclosed compartments.
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.7 - Page 39
102 Locations of openings where watertight integrity is
required, are illustrated in Appendix A.
103 The strength and arrangement of doors and hatches
and their frames as well as the capacity of the closing systems are to be sufficient to ensure efficient closing of
doors/hatches when water with a head of 2,0 m is flowing
through the opening, and at an inclication of 15 degrees in
any direction.
B 200
Internal openings
201 The means to ensure the watertight integrity of internal openings which are used during the operation of the unit
while afloat, are to comply with the following:
a) Doors and hatches which are freqnently used may normally be open if provided for remote closing from a
central control room on a deck which is above any final
waterline after flooding and are also to be operable locally from each side of the bulkhead. Indicators are to
be provided at the control room showing whether the
doors are open or closed.
b) The requirements regarding remote control in a) may be
dispensed with for those doors or hatch covers which are
normally closed, provided an alarm system (e.g. light
signals) is arranged, showing personnel in the control
room whether the doors/hatches in question are open or
closed. A notice is to be affixed to each such door or
hatch cover to the effect that it is not to be left open.
202 The means to ensure the watertight integrity of internal openings which are kept permanently closed during the
operation of the unit are to comply with the following:
A notice is to be affixed to each such closing appliance to
the effect that it is to be kept closed. Manholes fitted with
closely bolted covers need not be so marked.
203 Where valves are provided at watertight boundaries to
maintain watertight integrity, these valves are to be capable
of being operated from a control room. Valve position indicators are to be provided at the remote control station.
If the valves are remotely operated by means of mechanical
devices, operation from a deck which is above any final
waterline after flooding will be accepted. Valve position indicators are to be provided at the remote control station.
B 300
External openings
with indicators showing whether the openings are closed or
open.
B 400
Strength of watertight doors and hatches
401 Watertight doors and hatches for internal and external
openings are to be designed for a strength equivalent to or
better than required for the watertightness of the structure in
which they are positioned.
402 Provided flooding is a possible mode of failure based
upon the damage assumptions as given in Pt.3 Ch.2 Sec.6,
for compartments on both sides of a watertight door/hatch,
the watertight door/hatch is to be designed to withstand the
design pressure from both sides.
403 The design pressure is to be taken as the waterhead
corresponding to the vertical distance between the load point
and the deepest waterline after damage.
404 Plating.
The thickness of plating subjected to lateral pressure is not
to be less than:
t=
-
-
the lower edge of openings of air pipes (regardless of
their closing appliances) is to be above the damage waterline.
the lower edge of ventilator openings, doors and hatches
with manually operated means of weathertight closures
is to be above damage waterline, unless 303 is applicable.
openings such as manholes fitted with closely bolted
covers, and side scuttles/windows of the non-openiiJ.g
type with inside hinged deadlights may be submerged.
302 The requirements of 201 b) apply where the watertight
integrity is dependent on external openings which are permanently closed during the operation of the unit, while
afloat.
303 External doors and hatches of limited size may be accepted between the damage waterline and freeboard deck
provided they are watertight closable locally and by remote
operation of the closing appliances from the control room,
.JP
(mm)
)apkp
k,
= correction factor for aspect ratio of plate field
= (1,1 - 0,25 s//)2
= max. 1,0 for s/I = 0,4
p
= min. 0,72 for s/I = 1,0
= design pressure in kN /m2 corresponding to the head
"P
= 220 f 1 N /mm2
of water to damage waterline
~
is dependent on support condition
= 1, 0 for clamped edges
= 0,5 for simply supported edges
= stiffener spacing in m
= stiffener span in m
s
I
Guidance note:
The plating is normally assumed to be simply supported along
the edges.
---e-n-d---o-f--G-u-i-d-a-n-c-e--- n-o-t-e---
405
Stiffeners on doors and hatches.
The section modulus of panel stiffeners and edge stiffeners
is not to be less than
301 Where. watertight integrity is dependent on external
openings which are used during the operation of the vessel,
while afloat, they are to comply with the following:
-
15,8 ka s
Z=
2
10001 sp
map ks
(cm\ min. 15 cm
3
p
= design pressure in kN/m 2 corresponding to the head
s
l
= stiffener spacing in m
of water to damage waterline
stiffener span in m. For doors with stiffeners in one
direction only I is to be taken as the span length between cleat support points in door frame
m
8 if simply supported
12 if fixed at ends
"P = 240 f 1 N/mm2
k, is dependent on support condition.
k,
= 1,0 if at least one end is clamped
=
406
0,9 if both ends are simply supported
Minimum stiffness of door and hatch edge stiffeners.
Moment of inertia of the side element of the door is in general not to be less than the value given by the formula:
DET NORSKE VERITAS
4
I=8pa
(cm")
Rules for Mobile Offshore Units , July 1995
Page 40 - Pt.3 Ch.2 Sec. 7
where:
509
p
= packing line pressure along edges in N Imm, mini-
a
=
407
mum 5 N/mm
spacing of bolts or other securing devices in m.
Stiffness of door and hatch frames.
The frames are to have necessary. stiffness to avoid deflections resulting in leakage in the damage condition.
The frame shall be continuous on all four sides and shall be
designed to have a section moment of inertia on each side
of not less than the value given by the formula:
3
!=3,2pbh
4
(cm )
where:
p
=
design pressure in kN im2 corresponding to the head
b
h
=
=
the shorter dimension of the opening in m
the longer dimension of the opening in m.
Any failure to the remote control system is not to
cause opening of closed doors/hatches. Failure on one
door/hatch shall not put any other doors/hatches out of
function.
510 Power supply is to be a separate independent source
with stored energy for each door/hatch or a common redundant system with two independent sources capable of
closing at least 50 % of all doors/hatches in not more than
60 seconds.
511 The electrical power required for operation, control
and monitoring is to be supplied from emergency switchboard either directly or by dedicated distribution board situated above the area which may be flooded in damage
condition.
512 The power sources for operation, control and monitoring are to be monitored by alarm.
of water to damage waterline
C. Freeboard
408 Stresses in door and hatch frames and their connections to the supporting structure.
The stresses are not to exceed the following values:
Normal stresses = 220 f 1 N/mm2
Shear stresses = 120 f 1 N/mm2
The end connections of the frames and the supporting
structure are to be taken into consideration when calculating
the stress levels in the frames.
409 Cleatings (securing devices) are to be designed for sea
pressure acting on the opposite of which they are positioned.
B 500 Operation and control of watertight doors and
hatches
501 Frequently used watertight doors/hatches are to be
arranged for emergency remote closing according to the
principles given in 200.
502 -In addition to means for remote closing, it is to be
possible to open and close the doors/hatches locally from
both sides by use of e.g. mechanical device or hydraulic
system with stored energy. The stored energy may be a hydraulic accumulator connected to a centralized hydraulic
system by a non-return valve. The capasity is to be sufficient
for opening and closing the door/hatch three times.
503 The device for local operation is to be designed with
a neutral spring return position in which the doors/ hatches
are to stop closing and located easily accesible for the personnel passing the door/hatch way.
504 The movement of local operating device should be in
the same direction as the movement of door/hatch.
505 The arrangement is to be such that the door/hatch will
close automatically only if opened by local control after being closed from the central control station. The tota!e closing
time is not to be less than 30 seconds or more than 60 seconds.
506 Red lights are to be arranged for warning of personnel
locally operating the doors/hatches that these have been remotely closed.
C 100
General
101 The computation of freeboard is not subject for classification. It will however be necessary to observe the requirements below related to freeboard. The regulations of
relevant national authorities will also have to be observed.
The requirements, including those relating to certification,
of the International Convention on Load Lines 1966 (ILLC
1966) apply to all units. The minimum freeboard of units
which cannot be computed by the normal methods laid down
by that Convention will be determined on the basis of
meeting the applicable intact stability, damage stability and
structural requirements for transit conditions and drilling
operations while afloat. The freeboard is not to be less than
that computed in accordance with the ILLC 1966 where applicable.
102 The requirements of the ILLC 1966 with respect to
weathertightness and watertightness of decks, superstructures, deckhouses, doors, hatchway covers, other openings,
ventilators, air pipes, scuppers, inlets and discharges, etc.
are taken as a basis for all units in the afloat conditions.
103 The requirements to hatchways, doors and ventilators
are depending upon the position as defined in the ILLC
1966, Reg. 13.
C 200 Self-elevating units
201 Load lines for self-elevating units are calculated under
the terms of the ILLC 1966. When floating or when in
transit from one operational area to another, the units will
be subject to all the conditions of assignment of the ILLC
1966 unless specifically excepted. However, these units will
not be subject to the terms of the ILLC 1966 while they are
supported by the seabed or are in the process of lowering
or raising their legs. The regulations of relevant national
authorities will also have to be observed.
202 In general, heights of hatch and ventilator coamings,
air pipes, door sills, etc., in exposed positions aiid their
means of closing are determined by consideration of both
intact and damage stability requirements.
C 300
Column-stabilized units
507 An audible local alarm is to sound when the
doors/hatches is moving to closed position.
301
508 All watertight doors/hatches are to be provided with
positive means of indication which will show at a central
control station whether the doors/hatches are open or closed.
- the strength of the structure
- the air gap between waterline and deck structure
- the intact and damage stability requirements.
Load lines for column-stabilized units are based on:
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 Sec.7 -
Page 41
302 The conditions of assignment are to be based on the
requirements of the ILLC 1966. The regulations of relevant
national authorities will also have to be observed.
The doors are to be designed for a strength equivalent to or
better than that required for the weathertightness of the
structure in which they are positioned.
303 In general, heights of hatch and ventilator coamings,
air pipes, door sills, etc., in exposed positions and their
means of closing are determined by consideration of both
intact and damage stability requirements.
Doors should generally open outwards to provide additional
security against impact of the sea.
304 The freeboard deck (reference deck) is defined as the
lowest continuous deck exposed to weather and sea, which
has permanent means of closing and below which all
openings are .watertight closed at sea.
305 Side scuttles and windows, including those of non-opening type, or other similar openings, are not to be fitted
below the freeboard deck.
306 For the first tier on the freeboard deck, the requirements as for Position 2 in the ILLC 1966 apply with respect
to openings, sill heights, coaming heights and weathertight
closing appliances. Side scuttles and windows on first tier
need not be fitted with inside hinged deadlights if they are
not below damage waterline.
For the second tier weathertight closing appliances are required, but sill-/coaming heights may be omitted.
Above the second tier weathertight closing appliances are
required if openings give access to a space below the freeboard deck or a space included in the buoyant volume.
307 Deckhouses and wells on the first and second tiers
which are not weathertight closed as described in 306, are
generally to be provided with satisfactory drainage. The
totale drainage cross sectional area is not to be less than
0,30 % of the deck area for the deckhouse or well. The
drainage is to be arranged so that it will prevent accumulation of water in any part of the space.
202 Sill heights.
Openings as mentioned in 201 are in general to have a sill
height not less than 3 80 mm.
The following openings in position I are to have sill heights
not less than 600 mm:
- companionways
- openings in superstructures and in bulkheads at ends and
sides of deckhouses where access is not provided from
the deck above
- opernngs in engine casings.
D 300 Weathertight hatches and coamings
301 The minimum height of coamings for hatches with
weathertight covers is normally not to be less than:
- 600 mm in position I
- 450 mm in position 2.
302 Manholes and small scuttles with coaming height less
than given in 301 and flush scuttles may be allowed when
they are closed by watertight covers. Unless secured by
closely spaced bolts, the covers are to be permanently attached.
303 Coamings with height less than given in 301 may
normally be accepted for column-stabilized units after special consideration.
304 Hatch covers are to be mechanically lockable in open
position.
D. W.eathertight Closing Appliances
305 Materials for steel hatch covers are to satisfy the requirements given for structural material.
D 100 General
101 In this sub-section the requirements for the arrange-
Other material than steel may be used, provided the strength
and stiffness of the covers are equivalent to the strength and
stiffness of steel covers.
ment of weathertight openings and their closing appliances
are given. The closing appliances are in general to have a
strength at least corresponding to the required strength of
that part of the hull in which they are fitted.
For side scuttles and windows, however, the pressure head
is not to be taken less than 2,5 metres water column.
Guidance note:
Some requirements are also governed by the regulations in the
«International Convention of Load Lines 1966»:
-
307 The plating thickness depending on lateral pressure is
·given in Pt.3 Ch. I Sec.6.
The thickness of the top plating is not to be less than 6 mm.
308 The section modulus requirement of stiffeners is given
in Pt.3 Ch.I Sec.6.
309 The requirements to section modulus and moment of
inertia of hatch girders are given in Pt.3 Ch.I Sec.7.
doors in Ll2
definition of positions in Ll3
hatchways in L14-16
machinery space openings in Ll 7
miscellaneous openings in L 18
ventilators in L19
air pipes in L20
scuppers, inlets and discharges in L22
side scuttles in L23
freeing ports in L24
special requirements in L25-27.
D 400
Gaskets and closing devices
401 The requirements below apply to steel hatch covers
on weather decks with ordinary gasket arrangement between
hatch cover and coaming and gaskets arranged for vertical
gasket pressure in joints between cover elements.
Other gasket arrangements will be specially considered.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
102 Regarding locations of openings where weathertight
integrity is required, see Appendix A.
D 200
306 The design sea pressure on weathertight deck hatch
covers is given in Pt. 3 Ch. I Sec. 4 D.
Weathertight doors
201 Weathertight doors are to be of steel or equivalent
material.
402 The gasket material is to be of satisfactory air- and
seawater-, and if necessary, oil-resistant quality, effectively
secured along the edges of the cover.
The hatchway coamings or steel parts on adjacent covers in
contact with the gaskets are to be well rounded where necessary.
Where necessitated by the type and design of the unit, mass
forces from heavy covers or cargo stowed on the hatch
DET NORSKE VERITAS
Rules for Mobile Offshore Units, July 1995
Page 42 - Pt.3 Ch.2 Sec. 7
covers as well as forces due to sea pressure should be
transferred to the coaming or the deck by direct contact,
obtained by suitable devices, while sealing is achieved by
means of relatively soft gaskets.
403 The gaskets and securing arrangements are either to
be designed for the expected relative movement between
cover and coaming, or special devices are to be fitted to restrict such movement.
404 Panel hatch covers on weather decks are to be secured
by bolts, wedges or similar arrangement, suitably spaced
alongside the coamings and between the hatch cover sections.
405 Where hydraulic cleating is applied, the system is to
remain mechanically locked in closed position in the event
of failure of the hydraulic system or power supply.
406 Ordinary gasketed hatch covers are to be secured to
the coaming by a net bolt area for each bolt not less than:
2
A= 1,4 a (cm )
a
= spacing of bolts in m
The bolt diameter is not to be less than 16 mm.
407 The bolt diameter is not to be less than 22 mm for
hatchways exceeding 5 m in area.
408 Between cover elements the gasket line pressure is to
be maintained by a bolt area as given in 406.
409 For gasket line pressures exceeding 5 Nlmm, the net
bolt area is to be increased accordingly. The gasket line
pressure is to be specified.
410 Closing appliances of covers to hatches on exposed
decks with reduced coaming height will be specially considered.
General
101 Ventilators to spaces below free board deck or to
deckhouses closed weathertight are to have a coaming height
of at least:
- 900 mm in position 1
- 760 mm in position 2.
102 The thickness of ventilator coamings, air pipes, and
exhaust pipes is not to be less than given in the following
table:
105 Ventilators with coaming height of more than 4,5 m
in position 1, or more than 2,3 min position 2, need not be
fitted with closing arrangement.
Stability requirements may necessitate closing appliances.
Guidance note:
Special closing arrangement may be required by the National
Maritime Administration.
---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
106 The height of air pipes, measured from the deck to the
point where water may have access below, is not to be less
than 760 mm on freeboard deck and 450 mm on superstructure deck.
107 Where air pipes of heights as required in 106 will
cause difficulties in operation of the unit, a lower height may
be approved, provided the National Maritime Administration
are satisfied that the closing arrangement and other circumstances justify a lower height.
108 Openings of air pipes are to be provided with permanently attached efficient means of closing. The closing appliances are to be so constructed that damage to the tanks
by overpumping or occasionally possible vacuum by discharging is prevented.
109
All air pipes are to be well protected.
F. Inlets, Discharges and Scuppers
for direct manual operation by means of mechanical device
or permanently installed hand pump. Any valve serving a
sea inlet or a discharge below the load waterline is to be
remotely operated from above the damage waterline.
Discharges between load waterline and damage waterline
may be accepted with one locally closable non-return valve.
The valves are to be fitted as close to the inlet or discharge
as possible.
The controls shall be readily accessible and shall be provided with indicators showing whether the valves are open
or closed. All connections to sea are to be marked
SEA DIRECT.
102 The wall thickness of the pipes is to be as required in
204 and Pt.4 Ch.! Sec.6.
For self-elevating units:
External diameter
Wall thickness
mm
mm
$80
2'165
6
8,5
F 200 Discharges
201 Discharges leading through the shell either from
spaces below the freeboard deck or from spaces required to
be watertight above the freeboard deck, are to be fitted with
one automatic non-return valve at the outboard end with
positive means of closing located at a suitable position above
the damage waterline.
For column-stabilized units:
External diameter
104 The openings are to be provided with permanently
attached weathertight efficient means of closing.
F 100 Sea inlets and discharges in closed systems
101 Valves for sea inlets and discharges are to be arranged
E. Ventilators and Air Pipes
E 100
103 The deck plating in way of deck openings for ventilator coamings is to be of sufficient thickness and efficiently
stiffened.
mm
Wall thickness
above free.board deck
mm
$80
2'165
7,0
5
For intermediate external diameters the wall thickness is
obtained by lienar interpolation. Coamings with height exceeding 900 mm are to be supported by stays or equivalent
arrangements.
DET
202 If a septic tank is arranged in the system, a discharge
with inboard opening located lower than the uppermost load
line may be accepted when a loop of the pipe is arranged,
extended not less than 0,02L above the summer load waterline, where L is the length of the unit.
The outboard end is to be fitted with one automatic non-return valve with positive means of closing located above
damage waterline.
NORSKE VERITAS
Rules for Mobile Offshore Units, July 1995
Pt.3 Ch.2 Sec.7 -
Page 43
203
Discharges from spaces above the freeboard deck are
to be of steel or material specially resistant to corrosion.
103 Side scuttles below freeboard deck are to be of the
non-opening type with inside hinged deadlight.
204 The wall thickness of steel piping between hull plating
and a closable or non-return valve below freeboard deck is
not to be less than given in the following table:
104 Deadlights as required in 102 may be hinged outside,
provided there is easy access for closing.
External diameter
Wall thickness
mm
mm
:580
= 180
2:220
7,0
10,0
12,5
For intermediate external diameters the wall thickness is
obtained by linear interpolation.
105 No side scuttle is to be fitted in a position so that its
sill is below a line drawn parallel to the freeboard deck at
side and having its lowest point 0,025B above the summer
load waterline, or 500 mm, whichever is the greater distance. B is the breadth of the unit.
H. Testing of Doors and Hatches
Sec.6.
H 100 Pressure testing of watertight doors and hatches
101 Before installation (i.e. normally at the manufacturers)
206 Adequate arrangement is to be provided to protect
the watertight doors/hatches are to be hydraulically tested
from that side which is most prone to leakage.
205 General requirements for pipes are given in Pt.4 Ch. I
valves or pipes from being damaged.
207 The piping is to be of steel or equivalent material.
Valves and shell fittings are to be of steel, bronze or other
approved ductile material. Valves of ordinary cast iron are
not acceptable.
208 Where plastic piping is used the connection between
plastic and steel will be considered as the inboard opening.
F 300 Scuppers
301 A sufficient number of scuppers, arranged to provide
effective drainage, is to be fitted to all decks.
302 Scuppers on weather portions of decks and scuppers
leading from superstructures or deckhouses not provided
with weathertight closing appliances are to be led overboard.
303 Scuppers through the deck or shell are to comply with
requirements to material and thickness as given for discharges.
304 Scupper pipes are to be well stayed to prevent any
vibrations. However, sufficient possibility for expaiision of
the pipes is to be provided when necessary.
Test pressure = pressure height + 0,05 N/mm2 (5 m
H 20).
Acceptance criteria:
Doors/hatches with gasket: no leakage.
Doors/hatches with metallic sealing: maximum water leakage 1 litre per minute.
H 200 Hose testing of watertight and weathertight
doors and hatches
201 After installation onboard all watertight and weathertight doors/hatches are to be hose tested. The water pressure
is to be at least 0,2 N/mm2 (2 bar), and the nozzle is to be
held at a distance of maximum 1,5 metres from the
door/hatch. There is to be no leakage.
As an alternative to hose testing chalk testing may be accepted under special circumstances upon consideration by
the Surveyor in each case.
H 300 Function testing of watertight doors and hatches
301 After installation onboard the operation, control and
305 Scuppers from spaces below the freeboard deck or
alarm functions for all watertight doors and hatches are to
be tested to verify:
spaces within closed superstructures, may be led to bilges.
-
306 Scuppers leading overboard from spaces mentioned in
305 are to comply with the requirements given for discharges. Scuppers from exposed superstructure deck, led
through the vessel's sides and not having closable valves,
are to have wall thickness as required in F 204.
-
G. Side Scuttles and Windows
G 100 General
101 Side scuttles and windows made according to ISO
1751 and ISO 3903 with glass according to ISO 1095 and
tested according to ISO 614, will normally be accepted. The
same applies to national standards equivalent to the ISO
standards.
102 Side scuttles and windows in the first tier and second
tier if direct access below freeboard deck, are to have hinged
inside deadlights arranged so that they can be effectively
closed and secured watertight.
DET
-
that it is possible from the control room to close all
doors/hatches in one group simultaneously within 60
seconds
that it is possible to open and close the doors/hatches
three times by means of local advice and stored energy
that it is possible for a person to pass through the
doorway/hatchway and at the same time hold both handles in the- +=open position»
that it is possible to open the door/hatch locally from both
sides, after being closed centrally, and that the door/
hatch will close automatically after such opening
that the door/hatch will be mechanically locked in closed
position
that the light and sound signals give warning when the
door/hatch is closed centrally
that the remote position indicator for doors/hatches is
functioning properly
that the alarms for the following conditions function
properly:
- start of standby pump
- loss of power to control, alarm and indicating system
- low pressure (below lowest permissible).
NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Page 44 - Pt.3 Ch.2 App.A
APPENDIX A
CLOSING ARRANGEMENTS FOR DOORS AND HATCHES
Contents
C. Operation and Locking
A. Waterlines
A 100 Description of waterlines
C 100
101 The requirements to operation and locking of doors
and hatches are given in Table 1, in relation to the locations
defined in B.
B. Opening Location
B 100
General requirements
Description of location of openings
C. Operation and Locking
C 100 General requirements
A. Waterlines
LOAD LINE REQUIREMENTS
LOCATION OF OPENING$
A 100 Description of waterlines
101 The following waterlines are defined:
(lrd TIERI
Waterline A: Waterline showing equilibrium position at 1st
intercept between righting and wind heeling moment curves
in damage condition.
Waterline B: Waterline according to area requirement of
righting and wind heeling moment curves, either in intact
or damage condition, whichever is the most severe.
l2nd TIERI
(1~t
T!ERI
llI
lZ'.
Ill
B. Opening Location
B 100 Description of location of openings
101 The location of openings in relation to the waterlines
are defined as, (see Fig.!):
I
II
III
IV
v
VI
Internal openings in watertight bulkheads, i.e. internal bulkheads assumed watertight in stability calculations.
External openings below deepest draught according
to ILLC 1966.
External openings between deepest draught and
freeboard deck.
External openings above freeboard deck, submerged
before equilibrium position at 1st intercept (line A)
between righting and wind heeling moment curves
in damage condition.
External openings:
I) on first and second tier
2) submerged between equilibrium position at 1st
intercept (line A) and compliance with area requirement (line B).
External openings:
1) on and above third tier
2) above waterline B.
COLUMN STABILIZED UNITS
SELF-ELEVATING UNITS
STABILITY REQUIREMENTS
LOCATION OF OPENINGS
I
I
t
I
I
I
I
I
I
J__~~--'
Fig. 1
Location of openings
DET NORSKE VERITAS
Rules for Mobile Offshore Units , July 1995
Pt.3 Ch.2 App.A - Page 45
Table Cl Requirements regarding operation and locking of doors/hatches
Pressure side
Sliding I)
Location
of
opening
1aa111u,u
One
side
Both
sides
~
nnn1nn
x
Bolted
r:r D D
x
x
x
x
I
x
x
x
II
Type of door/hatch
Hinged
Rolling 2)
x
x
x
x
x
x
NA
III
NA
x
x
IV
x
x
x
x
x
v
x
x
x
x
x
VI
x
Local
Remote
x
x
x
x
x
x
x
x
x
x
x
x
x
NA
NA
NA
NA
x
Operation of
door/hatch
x
x
x
x 4)
x
x
x
x
x
x
x
x
x
x
x
x
NA
x
x
x
NA
NA
NA
NA
NA
NA
NA
x
x
x
NA
Locking
in
closed
position
Mechanical 3)
x
x
x
x
x
x
x
x
x
x
NA
NA
NA
x
x
x
x
x
NA means «not applicable ...
1) Sliding door:
Moving along and supported by trackway grooves, with built-in «mechanical"' locking due to the tapered form and friction, and a positive force
is required to reopen the doors
2) Rolling door:
Guided and supported by steel rollers with hydraulic cleating.
3) Mechanical locking:
By means of wedges, bars or similar devices which are self-locking.
4) The door/hatch is to be fitted with a notice board stating that the door/hatch is to be kept closed while the unit is afloat at sea (for self-elevating
units) and at sea {for column-stabilized units). The door/hatch may be only locally operable.
DET NORSKE VERITAS