INTERNATIONAL MARITIME ORGANIZATION
E
IMO
MARITIME SAFETY COMMITTEE
75th session
Agenda item 5
MSC 75/5/3
12 March 2002
Original: ENGLISH
BULK CARRIER SAFETY
Bulk Carrier Model Test Progress Report
Submitted by the United Kingdom
SUMMARY
Executive summary:
This document reports on results to date of the model tests initiated
following the Re-opened Formal Investigation into the loss of the
m.v. Derbyshire. It is concluded that whilst attention has been
focused on the vertical forces on hatch covers, the horizontal forces
on hatch covers and coamings are of equal importance.
Action to be taken:
Paragraph 20
Related documents:
MSC 74/5/1, SLF 44/4/10, MSC 75/5/1
Introduction
1
Towards the end of the Re-opened Formal Investigation (RFI) into the loss of m.v.
Derbyshire, the United Kingdom Government agreed to fund a programme of model tests at the
Maritime Research Institute, Netherlands (MARIN). The research programme was agreed
between the United Kingdom’s Maritime and Coastguard Agency (MCA) and Lloyds Register of
Shipping (LR), and supervised by both parties. MSC 74/5/1 reported on the progress of the
model test programme to March 2001. This paper reports on the progress since that date and
highlights some key results from the model tests and their subsequent analysis. A more detailed
report including proposals for changes to ILLC66 Regulation 16 will be made available to
SLF 45.
2
All the model tests are now complete. The key results have been analysed by Lancaster
University, who confirmed their initial conclusion that the best fit to the impact loads data was
given by the Generalised Pareto distribution. The results for each ship have been “pooled” to
improve the reliability and consistency of the data, and the impacts for No.2 hold paired with
those for No.1 hold. The preliminary results were discussed, in a conference organized by the
Royal Institution of Naval Architects (RINA)1 and sponsored by the United Kingdom’s
Department of Transport, Local Government and the Regions (DTLR), in October 2001.
Electronic copies of the MARIN and Lancaster University reports are available from the MCA
website at www.fsa.mcga.gov.uk .
1
Design and Operation of Bulk Carriers Post mv Derbyshire The Royal Institution of Naval Architects, London
9th-10th October 2001
For reasons of economy, this document is printed in a limited number. Delegates are
kindly asked to bring their copies to meetings and not to request additional copies.
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Selected hull forms
3
A total of 235 tests have been carried out in head, bow quartering and beam seas on three
models: two Capesize and one Panamax vessel. The principal particulars of the three vessels are
given in the following table and the body plans are shown on figure 1.
Scale
Length pp (m)
Breadth (m)
Depth (m)
Draft
Displacement (tonnes)
No of tests
Phase 1- SSRC Capesize
1:65
271.0
45.00
24.60
18.11
188,200
44
Phase 2 – New Capesize
1:50
270.8
47.25
25.40
18.7
204,588
118
Phase1
Phase 3 - Panamax
1:50
216.0
32.24
19.10
13.818
83,151
73
Phase 2
Phase 3
Figure 1 – Body Plans of MARIN models.
Test conditions
4
Figure 2 shows the range of conditions tested for each Phase of the programme, plotted
against the Buckley survivability wave envelopes for the Northern and Southern hemispheres2.
The test condition for the Japanese model tests reported in SLF 44/4/10 is also included for
comparison.
Figure 2 - Test conditions
20
18
Northern Hemisphere Survival
Southern Hemisphere Survival
Phase 1 Tests
Phase 2 test variant
Phase 3 tests
Japanese (SLF 44/4/10)
16
14
12
10
8
6
4
2
0
0
2
4
6
8
10
12
14
16
18
20
Tp (sec)
5
Figure 2 indicates that, in general, the MARIN test conditions are close to the Buckley
survivability envelope, but that the Japanese tests are some way below the envelope. Other test
conditions away from the survivability envelope were defined to test specific hypotheses, for
example whether travelling at higher speeds in lower sea states would produce higher loads
(which they did not).
2
The Design Wave Climates for World Wide Operation of Ships, Part 1: Establishment of Design Wave Climates.
WH Buckley, SNAME T7R Report r-50, 2001
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Vertical loads
6
In their paper to the RINA conference, referenced above, Sole and Milne filtered the
results for hatch No.1 to consider only the data derived from self propelled and zero speed tests,
and made a logical case to apply different probabilities of non exceedance (p values) to the loads
predicted by Lancaster University for the intact and damaged conditions in the different sea
states, as follows:
North Atlantic
PM spectrum
0.99
0.95
Intact
Damaged
Rotating Tropical Storm
Jonswap spectrum
0.95
0.90
7
A similar analysis has been carried out to that presented in the RINA paper, except that
the data for hatch No.2 is added. The loads at the appropriate value of ‘p’ were plotted on the
basis of the factor H from IACS UR S 21, taking the parameter df to the top of the hatch
coaming, as proposed by Sole and Milne. Figure 3 shows the loads plotted against H. Also
included for reference is the mean of 1/10 highest loads obtained at the two longitudinal positions
reported in SLF 44/4/10; however these loads extrapolated to ‘p’ values corresponding to the
above table will be considerably in excess of the other points in the figure.
Figure 3 - Vertical Loads plotted against parameter H from IACS URS 21
200
180
160
140
120
URS21
Phase 2 Intact No1 Hatch
Phase 2 Intact No 2 Hatch
Phase 2 FP flooded No 1 Hatch
Phase 2 FP flooded No2 Hatch
Phase 2 No 1 Hold flooded No1 Hatch
Phase 2 No 1 Hold Flooded No 2 Hatch
Phase 3 Intact No1 Hatch
Phase 3 Intact No 2 Hatch
Phase 3 FP Flooded No 1 Hatch
Phase 3 FP Flooded No 2 Hatch
Phase 3 No 1 Hold flooded No 1 Hatch
Phase 3 No 1Hold flooded No 2 Hatch
Phase 1 Intact No 1 Hatch
Phase 1 Intact No 2 Hatch
Phase 1 No Hold flooded No 1 Hatch
Phase 1 No1 Hold flooded No 2 Hatch
Japanese 1/10 values (SLF 44/4/10)
SLF 44/4/10
Power (URS21)
100
80
60
URS21
40
20
0
0
2
4
6
8
10
12
14
H
8
Figure 3 confirms that the vertical loads are well in excess of URS21, and the need for
reconsideration of that standard. It is considered that the loads in damaged conditions, at a
suitable reduced probability from the intact conditions, should be included in any revision of that
standard. The original UR S21is based on intact conditions only, but inspection of the above
figure shows that the loads from the intact conditions are in excess of UR S21.
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9
The inclusion of design speed within the formula for factor H is also of concern, as the
influence of speed is unclear from evidence from these tests. Figure 4 shows the impact of speed
on the Phase 2 loads in the intact condition.
Figure 4 - Effect of speed on vertical load
70
Phase 2 - Intact
p=0.99
60
50
40
Zero Speed
30
Speed = 13.5 knots
Speed = 15.5 knots
20
10
0
15
13.18
12.55
10
15
13.18
13.18
Bow quartering seas
Head seas
Significant wave height (m)
10
Figure 4 indicates that the effect of calm water speed on vertical load is not consistent
across the range conditions tested, and further work is required to assess whether calm water
speed is a primary or secondary parameter in relation to vertical loads.
Horizontal loads
11
Loads were also measured by MARIN in the longitudinal and transverse directions and
some of this data has been analysed by Lancaster University. Figures 5 and 6 show the
maximum loads measured by MARIN for all three components for Phases 2 and 3 respectively
for head and bow quartering seas.
Figure 5 - Distribution of loads along the length of Phase 2 (Cape size) vessel
250
Note:
L are Longitudinal Loads
T are Transverse Loads
V are Vertical Loads
No 1 Hatch
200
L
No 5 Hatch
No 2 Hatch
L
150
L
V
T
T
100
T
V
50
V
0
0.5
0.4
0.3
0.2
0.1
0
x/L from FP
Figure 6 - Distribution of the loads along length of Phase3 (Panamax) vessel
350
No 1 Hatch
Note:
L are Longitudinal Loads
T are Transverse Loads
V are Vertical Loads
L
300
250
No 2 Hatch
200
No 4 Hatch
L
L
150
T
100
V
T
T
V
50
V
0
0.5
0.4
0.3
0.2
x/L from FP
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0
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12
Figures 5 and 6 indicate that the longitudinal load on the forward coaming of No 1 hatch
is between 2 and 3 times the vertical load. Also whilst the vertical load reduces towards
midships, the longitudinal load reduces to a lesser extent, and on the Phase 2 Capesize the
maximum longitudinal load recorded at No.5 hatch is greater than that at No.2 hatch. In both
cases the transverse loads at No.1 hatch appear to be a similar order of magnitude to the vertical
loads, and again reduce in magnitude more slowly towards midships.
13
Further analysis of the longitudinal loads against the corresponding vertical load for hold
No.1 indicate a linear trend, for both vessels, but at a different ratio, as shown in figure 7 below.
MARIN noted that the magnitude of the longitudinal forces appeared constant irrespective of
freeboard. Further work is required to clarify the reasons for this difference, and to develop a
simple way of estimating the longitudinal load from a calculated vertical load. Industrial sources
indicate that the limiting load for hatch covers to avoid longitudinal displacement is about 45kPa,
well below the longitudinal forces predicted from the model tests. Any revised standards
therefore need to take into account the longitudinal forces.
Figure 7 - Longitudinal Loads for Hold 1 for Phase 2 and 3 models
450
Phase 2 Bow seas
Phase 3 Bow Seas
400
Linear (Phase 2 Bow seas)
y = 2.8297x + 102
Linear (Phase 3 Bow Seas)
350
300
250
y = 0.6304x + 99.56
200
150
100
50
0
0
20
40
60
80
100
120
140
Vertical Load (kPa)
14
The longitudinal forces for hold No.2 can be estimated as a proportion of those for hold
No.1 (about 83% for the Capesize and 68% for the Panamax). This could be influenced by the
way in which the data was paired in the Lancaster University analysis, but appears consistent
with the MARIN values.
Beam seas tests
15
A total of 11 tests were run for beam seas using the Phase 1-3 models, in the intact
conditions, and 1 with No.1 hold flooded using the Phase 1 model. The sea conditions were
chosen to give wave periods straddling the natural rolling period of each vessel, with the
corresponding significant wave heights selected to be as close to the survivability envelopes as
practicable.
16
Figure 8 shows the transverse loads plotted against a numeral, which takes into account
both the local freeboard and the location along the length of the vessel, and appears to take into
account in a logical manner the different loads associated with the Capesize and Panamax
vessels. The MARIN data for No.1 hold has not been analysed by Lancaster University, but the
data as a whole shows a similar trend. It is anticipated that Figure 8 can be developed to provide
a complete picture of the distribution of transverse loads in beam seas along the length of the
vessel.
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Figure 8 - Transverse loads in beam sea conditions
300
Cape Size No 2 Hold
Cape Size No 5 Hold
Panamax No 2 Hold
Panamax No 4 Hold
250
200
150
100
50
0
10
9
8
7
6
5
4
3
2
1
0
df*Sqrt(2x/L), where df is from URS21 to top of hatch cover and x/L from FP
Hatch cover design standards
17
The United Kingdom considers that the results of this work should be used to develop up
to date environmental loads, for hatch cover fastenings in the longitudinal and transverse
directions, as well as for covers vertically. An update to UR S21 is considered an essential
element in this process.
18
Whilst beam seas may be less important for Capesize and Panamax vessels with their side
rolling hatch covers, they are significant for smaller vessels with longitudinally folding covers,
and it is considered that further analysis is necessary to validate beam sea results on smaller
vessels.
19
MSC 75/5/1 provides a progress report on the International Collaborative FSA Study on
Bulk Carriers, and focuses on the initiating events and associated fatalities. It notes that a
number of hatch cover failures have been initiated by side shell failure causing an internal
pressure on the cover, and also notes that most fatalities occur after hatch cover failure.
Consideration should then be given to means of relieving internal pressure, on covers not
designed to withstand it, to avoid hatch cover failure.
Action requested of the Committee
20
The Committee is invited to consider the above results and to instruct the Bulk Carrier
Working Group to be established at this session to:
.1
review the work undertaken to date;
.2
endorse the proposal to update the hatch cover design environmental load criteria
in the ICLL66; and
.3
concur that the SLF Sub-Committee should be instructed to take this into account
when it is revising the ICLL 66.
____________
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