Propulsors in Ice
July 2012
Rule Note
NR 584 DT R00 E
Marine Division
92571 Neuilly sur Seine Cedex – France
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BV Mod. Ad. ME 545 k - 17 December 2008
RULE NOTE NR 584
NR 584
Propulsors in Ice
SECTION 1
July 2012
PROPULSORS IN ICE
Section 1
Propulsors in Ice
1
General
1.1
1.2
1.3
1.4
2
5
Ice load scenarios
Design ice loads
Design on propulsor
8
General
Propeller
Propulsion shaft line
Steering system
Electrical installation
5.1
2
Materials exposed to sea water
Materials exposed to sea water temperature
Other components
Machinery design
4.1
4.2
4.3
4.4
5
5
Ice interaction
3.1
3.2
3.3
4
Application
Documentation to be submitted
Definitions
Arrangement
Materials
2.1
2.2
2.3
3
3
9
General
Bureau Veritas
July 2012
NR 584, Sec 1
SECTION 1
PROPULSORS IN ICE
Symbols
A
: Steering arm, in m, defined in Fig 4
Ch
: Height coefficient, defined in [3.2.6]
D
: Propeller blade diameter, in m
1.2.1 The documents to be submitted, for approval or for
information, to the Society are listed in Tab 2.
h
: Actual crushing contact height, in m, defined in
[3.2.6]
1.3
hice
: Maximum ice sheet thickness, in m, defined in
[3.2.3]
Qmax
: Maximum torque on a propeller due to ice-propeller interaction, in N⋅m
R
: Propeller radius, in m
Rh
: Radius of curvature, in m, defined in [3.2.6]
rf
: Rafting factor, defined in [3.2.4]
ReH
: Minimum yield stress of the material, in N/mm2
σ0.2
: 0,2% proof stress, in N/mm2
σAll
: Allowable stress, in N/mm2
σice
: Uniaxial compressive strength of ice, in N/mm2,
defined in [3.2.5]
Tsteer
: Steering torque, in N⋅m
Trv
: Hydraulic steering torque, in N⋅m
W
: Effective width, in m, of the propulsor collecting
ice load.
1
1.2
Definitions
1.3.1 Propulsor
A propulsor is a propulsion device underneath the hull of a
ship, attached to the ship by a strut which carries one or
more propeller with or without nozzle.
1.3.2 Podded propulsor
A podded propulsor is a propulsor with the prime mover
installed inside a pod and directly coupled to the propeller
shaft, see Fig 1.
1.3.3 Geared propulsor
A geared propulsor is a propulsor mechanically geared with
the prime mover located outside the propulsor, see Fig 2.
1.3.4 Strut
The strut is the structure employed to attach the pod to the
hull support, it may have a rudder or column shape.
1.3.5 Hull support
The hull support is the part of the propulsor which is connected to the ship structure.
1.3.6 Azimuth propulsor
An azimuth propulsor is a propulsor which has the capability to rotate through 360° in order to develop thrust in any
direction.
General
1.1
Documentation to be submitted
Application
1.1.1 Requirements of this Rule Note apply, in addition to
the general requirements listed in Tab 1, to the following
types of propulsors intended for navigation in ice-infested
waters:
• podded propulsor, with or without nozzle
• geared propulsor, with or without nozzle.
1.3.7 Steering unit
The steering unit includes:
• the power actuating systems
• the components used for the transmission of power to
the strut (such as gear drives, worm drives, etc.)
• the slewing bearing and the sealing system in way of the
hull penetration.
Table 1 : General requirements applicable to propulsors
Application to ships assigned with a notation
Rules (1)
ICE CLASS
POLAR CLASS or Icebreaker
NR467 Rules for the Classification of Steel Ships, Part B
Yes
Yes
NR467 Rules for the Classification of Steel Ships, Part C
Yes
Yes
NR467 Rules for the Classification of Steel Ships, Pt E, Ch 8, Sec 3
Yes
No
NR527 Rules for the Classification of POLAR CLASS and Icebreaker Ships
No
Yes
(1)
NR467 Rules for the Classification of Steel Ships, hereafter referred to as Rules for Steel Ships
NR527 Rules for the Classification of POLAR CLASS and Icebreaker Ships, hereafter referred to as NR527.
July 2012
Bureau Veritas
3
NR 584, Sec 1
Table 2 : Documentation to be submitted
Item n°
I/A (1)
Document (2)
1
I
General arrangement of the propulsor
2
I
General layout of the propulsor
3
A
Structural drawings of the propulsor
4
A
Failure Mode and Effects Analysis of the propulsion and steering functions of the propulsor
5
I
Maximum propulsive power as function of pod steering angle and shaft rotational speed
6
I
Stresses calculation
7
I
Operation manual of the propulsor
8
A
For propeller, documents as per NR527 or the Rules for Steel Ships, Part E, as applicable
9
A
For propeller shaft, detailed drawing including the brake
10
I
General arrangement of the steering system
11
A
Detailed drawings of the main components of the steering system, including locking device
12
I
Installation drawing of the bearings
13
I
Bearing data (maximum allowable static and dynamic load capacity, permissible rotational speed range, axial
displacement, operating conditions...)
14
I
Environmental conditions
15
I
Dynamic load calculation of bearings
16
I
Lifetime calculation of bearings
(1)
(2)
A = to be submitted for approval
I = to be submitted for information.
Diagrams are also to include the control and monitoring systems and automation systems, when applicable.
Figure 1 : Podded propulsor
Figure 2 : Geared thruster
Hull supports
Hull support
Strut
Strut
Pod
Pod
1.3.8
Steering power unit
1.4
A steering power unit is:
• In case of electric steering: a converter and its associated electrical equipment.
• In case of hydraulic steering: an electric motor and its
associated electrical equipment and connected pump.
1.3.9
Steering power actuating system
• In case of electric steering: an electric motor and its
associated electrical equipment.
• In case of hydraulic steering: the hydraulic equipment
provided for supplying power to turn the steering column, comprising a steering power unit or units and the
associated pipes and fittings and the hydraulic motor.
Propulsor redundancy
At least two propulsors are to be fitted in ships where these
are the sole means of propulsion. Single propulsor unit
installations are specially considered by the Society on a
case by case basis.
1.4.2
A steering power actuating system is:
4
1.4.1
Arrangement
Propulsor availability
Propulsors are to be arranged so that the failure of one unit
does not render the other inoperative.
The steering system of each propulsor is to include at least
two power actuating systems.
The essential components of the auxiliary systems (lubrication, cooling, ventilation, hydraulic systems) serving the
propulsor are to be duplicated.
Bureau Veritas
July 2012
NR 584, Sec 1
Means (such as a brake) are to be provided to hold the shaft
where necessary to avoid any situation which could be detrimental to some components of the propulsor when it
becomes inoperative (e.g. in case of bearing failure).
2
Materials
2.1
Materials exposed to sea water
Ice interaction
3.1
Charpy V impact test is to be carried out for materials other
than bronze and austenitic steel materials. Test pieces taken
from the propeller castings are to be representative of the
thickest section of the blade. An average impact energy
value not to be less than 20 J taken from three Charpy V
tests is to be obtained at −10ºC.
Ice load scenarios
3.1.1 Both transversal and axial ice load cases are to be
covered. The following cases are to be calculated:
• transversal force:
-
on strut
-
on pod
-
on nozzle, if applicable
• axial force:
Materials exposed to sea water
temperature
2.2.1 Materials exposed to sea water temperature are to be
of steel or other approved ductile material. An average
impact energy value not to be less than 20 J taken from
three tests is to be obtained at −10ºC.
Other components
2.3.1 For the requirements relative to materials intended for
other parts of the propulsor such as gears, shaft, couplings,
etc., refer to the applicable Parts of the Rules for Steel Ships.
3
2.1.1 Materials exposed to sea water, such as propeller
blades, are to have an elongation not less than 15% on a
test piece the length of which is five times the diameter.
2.2
2.3
-
on strut
-
on pod
-
on nozzle, if applicable.
3.1.2 Scenarios
The critical scenarios for ahead and astern working ships
are shown in Tab 3 and Tab 4, respectively.
For propulsor located at bow ship, astern working ship has
to be considered as ahead working ship.
Table 3 : Critical scenarios for ahead working ships
N°
1a
Description
N°
Crushing ice sheet at bracket top
1b
Ice sheet
Ice sheet
Crushing ice sheet at propeller hub
2b
Crushing ice sheet at propeller hub
Ship motion
Ship motion
Ice sheet
3
Crushing ice sheet at bracket top
Ship motion
Ship motion
2a
Description
Ice sheet
Crushing ice sheet at bracket, propulsor turned 90°
4
Ship motion
Crushing ice sheet on propulsor, propulsor turned 90°
Ship motion
Ice sheet
Ice sheet
July 2012
Bureau Veritas
5
NR 584, Sec 1
Table 4 : Critical scenarios for astern working ships
N°
5a
Description
N°
5b
Crushing ice sheet at bracket top
Description
Crushing ice sheet at bracket top
Ship motion
Ship motion
Ice sheet
6a
Ice sheet
Crushing ice sheet at lower bracket
6b
Crushing ice sheet at lower bracket
Ship motion
Ship motion
Ice sheet
Ice sheet
e
Ic
ee
et
sh
e
sh
Ice
t
7
Crushing ice sheet on strut
8
Crushing ice sheet on pod
Ship motion
Ship motion
Ice sheet
Ice
sh
t
ee
Ice sheet
9a
Grounding (blade failure)
9b
Grounding (blade failure)
Ship motion
Ship motion
3.2
Design ice loads
Table 5 : Ice coefficients k1 and k2
3.2.1 General
The design ice load is characterized by a force distributed
over a rectangular load patch of dimension h and W.
3.2.2 Ice coefficients k1, k2
Ice coefficients k1 and k2 to be used for estimation of ice
force are given in Tab 5.
3.2.3 Maximum ice sheet thickness hice
Ice thicknesses hice, in m, to be used for estimation of ice
force are given in:
• Tab 6 for ships assigned with a notation ICE CLASS
• Tab 7 for ships assigned with a notation POLAR CLASS
• Tab 8 for ships assigned with a notation Icebreaker.
6
Bureau Veritas
k1
k2
1
1,21
0,83
2
1,21
0,83
3
1,21
0,83
4
0,67
1,00
5
0,67
1,00
6
0,67
1,00
7
0,67
1,00
ICE CLASS IA SUPER
0,67
1,00
ICE CLASS IA
0,67
1,00
ICE CLASS IB
0,67
1,00
ICE CLASS IC
0,67
1,00
Notation
POLAR CLASS
or
Icebreaker
July 2012
NR 584, Sec 1
Table 6 : Maximum ice thickness hice for ships
assigned with a notation ICE CLASS
Notation
hice, in m
ICE CLASS IA SUPER
1,0
ICE CLASS IA
0,8
ICE CLASS IB
0,6
ICE CLASS IC
0,4
3.2.5
Uniaxial compressive strength of ice over a
reference area
Uniaxial compressive strength of ice σice , in N/mm2, to be
used for estimation of ice force is given in Tab 10.
Table 10 : Uniaxial compressive strength of ice σice
σice , in N/mm2
Notation
Table 7 : Maximum ice thickness hice for ships
assigned with a notation POLAR CLASS
POLAR
CLASS
POLAR CLASS
or
Icebreaker
hice, in m
Icebreaker assisted
operations / In open ice
In close ice
1
3,5
2,0
2
3,0
1,5
3
2,5
1,2
4
1,5
1,0
5
1,0
0,8
6
0,8
0,6
7
0,6
0,4
3.2.6
1
9,0
2
8,0
3
7,0
4
6,5
5
6,0
6
5,6
7
5,6
ICE CLASS IA SUPER
5,6
ICE CLASS IA
5,6
ICE CLASS IB
5,6
ICE CLASS IC
5,6
Actual crushing contact height h
Actual crushing contact height h, in m, is defined as follows:
Table 8 : Maximum ice thickness hice for ships
assigned with a notation Icebreaker
h = rf ⋅ Ch ⋅ hice
hice, in m
Icebreaker
Winter/Spring
1
3,5
3,0
2
3,0
2,5
3
2,5
1,8
4
1,8
1,2
5
1,2
1,0
6
1,0
0,8
Rh / hice (1)
Concave
Convex
0,6
< 1,0
1,00
0,10
≥ 1,0 and < 1,5
0,60
0,20
7
3.2.4
where:
Summer/Autumn
0,8
rf
: Rafting factor defined in [3.2.4]
hice
: Ice thickness, in m, defined in [3.2.3]
Ch
: Height coefficient, given in Tab 11.
Table 11 : Height coefficient Ch
Rafting factor rf
Rafting factor rf to be used for estimation of ice force is
given in Tab 9.
(1)
Table 9 : Rafting factor rf
≥ 1,5 and < 2,0
0,32
0,23
≥ 2,0
0,25
0,25
Rh
: Radius of curvature of the structure, in m, as
defined in Fig 3.
Astern
working ship
Figure 3 : Radius of curvature
1
1,14
1,14
Rh = 0,5 hice
2
1,16
1,09
3
1,20
1,04
4
1,66
1,33
5
2,00
1,48
6
2,18
1,49
7
2,50
1,50
ICE CLASS IA SUPER
1,75
1,17
ICE CLASS IA
1,87
1,31
ICE CLASS IB
2,00
1,48
ICE CLASS IC
2,50
1,50
POLAR CLASS
or
Icebreaker
Concave
Ice sheet
Convex
hice
July 2012
hice
Ahead
working ship
Notation
Bureau Veritas
Rh = 0,5 hice
Ice sheet
7
NR 584, Sec 1
3.2.7
Ice sheet crushing load Fc
Table 13 : Load cases for astern acting ships
2
The ice pressure pice in the contact area is given, in N/mm ,
by:
Force
Critical
scenario (1)
7
Fc
5a
W = strut width
8
Fc
5b
W = strut width
For ship with ICE CLASS notation or POLAR CLASS 4-7 or
Icebreaker 4-7:
• if Ac ≤ 1 m2:
p ice = σ ice ( k 1 – k 2 log A c )
2
• if Ac > 1 m :
k1
p ice = σ ice ⋅ --------Ac
For ship with POLAR CLASS 1-3 or Icebreaker 1-3 notation:
9
Fc
6a
W = strut width
10
Fc
6b
W = strut width
11
Fc
7
W = strut length
12
Fc
8
W = pod length
13
Fex
9a
/
14
Fex
9b
/
(1)
p ice = σ ice ( k 1 – k 2 log A c )
Dimension
A=h⋅W
Load
case n°
See Tab 4.
where:
3.3.2
Ac
It is to be checked that the stress in propulsor structure is
less than, or equal to, σALL as defined in Tab 14.
: Effective contact area, in m², equal to:
Ac = h ⋅ W, with h as defined in [3.2.6]
k 1 , k2
Checking criterion
Table 14 : σALL values
: Ice coefficients, defined in [3.2.2].
The ice sheet crushing load Fc , in MN, is given by:
Fc = pice ⋅ Ac
3.2.8
Blade failure load Fex
4
Hull support
Other structures
0,5 ReH
ReH
Machinery design
The ultimate load resulting from blade failure Fex as a result
of plastic bending around the blade root is to be calculated
as per NR527, Sec 3 or as per the Rules for Steel Ships, Pt E,
Ch 8, Sec 3, as applicable.
4.1
3.3
The propulsor is to deliver the required capabilities of prime
movers.
Design on propulsor
3.3.1
Load cases
The calculated forces described in [3.2] are to be applied as
uniform pressure distribution to an area on the structure of
the propulsor. The stresses are to be determined by static FEanalysis or any other acceptable alternative method.
The FE model is to include pod and strut up to slewing bearing level.
The load cases to be considered are given in:
• Tab 13 for an astern acting ship.
Table 12 : Load cases for ahead acting ships
8
Dimension
A=h⋅W
Load
case n°
Force
Critical
scenario (1)
1
Fc
1a
W = strut width
2
Fc
1b
W = strut width
3
Fc
2a
W = pod width
4
Fc
2b
W = hub diameter
5
Fc
3
W = strut length
6
Fc
4
W = pod length
See Tab 3.
Main propulsion
The propulsor is to deliver the required capabilities for
acceleration loads due to ship/ice interaction.
4.2
Propeller
4.2.1 Propellers are to comply with the relevant provisions
of:
• the Rules for Steel Ships, Pt C, Ch 1, Sec 8 and Pt E, Ch
8, Sec 3 for ICE CLASS notation
• NR527, Sec 3, [4.3] for POLAR CLASS or Icebreaker
notation.
• Tab 12 for an ahead acting ship
(1)
4.1.1
General
4.3
4.3.1
Propulsion shaft line
Design loads on propulsion line
Design loads, maximum ice thrust, maximum response
thrust, torque, response torque in the propulsion system, are
calculated according to the Rules for Steel Ships, Pt E, Ch 8,
Sec 3 or NR527, as applicable.
4.3.2
Design
The strength of the propulsion line is to be designed according to the pyramidal principle: the loss of the propeller
blade is not to cause any significant damage to other propeller shaft line components.
Bureau Veritas
July 2012
NR 584, Sec 1
4.4
b) Propulsor in a conventional bow ahead vessel
Steering system
The steering torque Tsteer required to keep the propulsor
steady during a heavy milling event is calculated as item
a) above.
4.4.1 Required steering torque of ice propulsors
a) Propulsor in a double acting ship
The steering torque Tsteer required to keep the propulsor
steady during a heavy milling event is given by:
If the propulsor is never used to actively mill the ice in
astern or transverse motion, a reduction of 20% of the
steering torque may be applied.
Q max ⋅ A
T steer = ------------------0, 5R
where:
A
: Arm, in m, as defined in Fig 4.
Arrangements are to be made to avoid any overload of
steering system.
For hydraulic steering systems, a 25% margin against
relief valve opening is to be used:
Trv = 1,25 Tsteer
Figure 4 : Arm
c) The available steering torque is to be high enough to
allow satisfactory operation in open water, see the Rules
for Steel Ships, Pt C, Ch 1, Sec 11.
4.4.2
Steering gear is to be protected by effective means limiting
excessive torque caused by plastic bending of one blade in
the worst position (related to steering gear).
5
Electrical installation
5.1
F
0,5R
A
Steering gear
General
5.1.1 Electrical equipments fitted in the propulsor are to be
suitable for operation at low temperature.
5.1.2
Electric propulsion plant
In case of an electric motor inside the pod, the propulsor is
to comply with the requirements of the Rules for Steel
Ships, Pt C, Ch 2, Sec 14, [7].
July 2012
Bureau Veritas
9
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July 2012