RO-RO SAFETY
S U B D I V I S I O N AND S T A B I L I T Y PROGRAMME F I N A L REPORT
RO-RO SAFETY
SUBDIVISION & STABILITY PROGRAMME
TASK 1 - SHIP GEOMETRY
INDEX SECTION PAGE 1. INTRODUCTION 5 2. WORK SCHEDULE 7 3. GEOMETRY COMPUTATIONS 10 4. CAPSIZE SITUATIONS 19
5. VEHICLE DECK ARRANGEMENTS 25
6. SURVIVAL PREDICTION 30
7. DISCUSSION 33
FIGURES
1. Arrangement of Basic Shiip (Ship 1)
2. Variations of Casings and Bullcheads on M a i n Declc a) Existing Casings
b) Modified Casings
c) Modified Casings with Transverse Bulkheads over full breadth.
d) Transverse Bulkheads
3. Service Variations in Draft and Trim a) Winter
b) Summer
4. Distribution of D r a f t
5. Distribution of Passenger Numbers against Draft
6. G Z Curves for Intact Ship (Draft & G M Variation)
7. G Z Curves for Intact Ship (Basic Ship at Load Draft)
' 8 . G Z Curves for Intact Ship (Modified Ship)
9. G Z Curves for Intact Ship (Modified Ship with Superstructure)
10. Water on Deck for Basic Ship
12. Damaged Ship ( A l l Compartment Pairs as built) a) G Z curves with no trim.
b) G Z curves with 0.50m trim by stern. c) G Z curves with 0.30m trim by bow. d) Damaged Freeboard and GMs.
13. G Z Curves for Damage 56 (E.R. + Tunnel Space) a) Load Draft No Trim
b) Variation of Draft c) Variation of T r i m d) Variation of K G .
14. G Z Curves for Damage 67 (E.R. + Aux. Machinery).
15. G Z Curves for Damage 78 (Aux. Machinery + Alternator Room).
16. Residual Damage Stability G M Requirements.
17. Improved Geometry sketches.
APPENDICES
1. Particulars and Cross Sections of Sample Vessels.
2. Survival Prediction.
SECTION 1
1. INTRODUCTION
The origmal intent of Task 1 was to investigate existing and possible new ship geometries i n an attempt to quantify the likely effect on R o / R o passenger ship design of the adoption of alternative standards of residual stability by the I M G . (These alternative criteria will be the subject of further consideration at the I M G in September).
In discussions between the GCBS and the Department of Transport it was agreed that the area to be studied in Task 1 be widened to investigate the potential problem of water ingress onto vehicle decks and the dangers of rapid capsize, also to study possible improvements in vehicle deck arrangements.
SECTION 2
2. WORK SCHEDULE
2.1 General arrangement drawings and stability information were obtained for nine passenger Ro-Ro vessels judged to be representative of the U K fleet.
The arrangements of each vessel were examined in a quahtative manner to enable an assessment to be made of possible variations in geometry on the bulkhead deck. Advantages and disadvantages of possible alternative geometries were noted. These are reported i n Section 5.
Basic particulars and cross sections of each of the nine vessels e.xamined are shown at Appendix 1.
2.2 Ship 1 was selected as being representative of vessels built to U K requirements for standards of residual stability, also suitable for variations of geometry as examined in 2.1 and for investigation of the influence of reserve buoyancy at higher levels on survival capability. Section 3 reports the results of computations of G Z values for the vessel as built and with modifled geometry both intact and damaged.
2.3 Statistics of incidents leading to capsize were examined and Section 4 comments on the influence of ship geometry on ability to resist capsize following incidents other than side damage or contact.
'2.4 Computaflons were made of 'a' and 'p' values for seven passenger Ro-Ro vessels from which it was determined that the probabilifles of single, double or triple compartment damages to Ship 1 were representaflve of current designs. A method is proposed in Section 6 by which the value of alternative geometries can be assessed i n providing resistance to slow or rapid capsize.
2.5 Log book records of Ship 1 were analysed for a full years operation to provide information to assist i n evaluadon of risk including
:-i) Passengers carried per voyage, average during one years operation.
ii) Variation of passenger numbers with draught and trim for each voyage (112 in total) during typical summer and winter periods of one week.
See figures 3 a), 3 b), 4 and 5.
2.6 Vessel informadon was made available to TQMS for work on Task 2 including data to assist in computation of survival capability of one freight Ro-Ro vessel, and informadon to assist in A265 calculation of attained index for one passenger Ro-Ro vessel.
SECTION 3
GEOMETRY COMPUTATIONS
3. GEOMETRY COMPUTATIONS
3.1 A cross channel ferry (Ship N o . l ) certified for 1,400 passengers and with vehicles carried at two levels and for which information was readily available was selected f r o m the sample for variation of geometry. Figure 1 shows an outline arrangement and the principal pardculars are listed
below:-Length B.P. 120.7m Length W.L. 125.5m Breadth (Mid) 21.0m Depth to Main Deck 6.4m
Depth to Upper Deck 11.8m Sheer Fwd & A f t 1.0m Max. Load Draft 5.00m (Mid) Displacement 7783 Tonnes
3.2 Longitudinal & Tran.sverse Subdivision of Main Vehicle Deck
The existing ship, as built, has narrow machinery casings on both sides above the subdivision ("D") deck carried up to the next ("C") deck where 3.8m wide casings with accommodadon are fitted. This accommodation is repeated on the next two decks up to the boat deck outboard of the upper vehicle space (see fig. 2a).
Full breadth passenger accommodation is fitted above this level.
Stability, both intact and damaged was investigated for the above arrangement as well as for one with wide longitudinal casings carried down to the "B" deck, referred to as "modified casings" (fig. 2b). This arrangement with added transverse watertight bulkheads across the car deck at frames 49, 89 and 130 forms the hybrid arrangement of fig 2c. Fig 2d shows a final arrangement with the three transverse bulkheads and no side casings.
The aft two transverse bulkheads were positioned above main W.T. bulkheads where i t was anticipated they would most improve the worst case of damage. The forward bulkhead was positioned over the W.T. bulkhead nearest to the centre of the remaining volume. The spacing of bulkheads is thus about 28 metres. The 'as built' side accommodadon casings were assumed to be divided at the same positions
as the bulkheads as shown in fig. 2a. The same division was made to the modified casings i n arrangements b and c.
Note that these casings are 3.8m fiom the side shell and thus fiom the waterline between frame 30 to frame 100 and are within the B/5 line for about half the length
of the ship. The B/5 line itself was ignored, and damage investigated both for an intact casing and a damaged casing.
3.3 Effect of Superstructure
The various arrangements described above have been investigated with and without superstructure. The stability book uses cross curves of stability for the hull to the upper deck. I f the intact ship heels to beyond 3 7 ° , at which point the upper deck is immersed, the superstructure extending between frames 24 and 155 will contribute to stability, pardeularly i n the case of a rapid heel and with the superstructure undamaged. Water would eventually find its way through the weathertight garage doors at each end of the superstructure and through vendlation openings, fire doors, and by up-flooding, but flnal capsize would be delayed. In the event of damage this superstructure would be immersed earlier to beneflt the G Z curve fiom between 3 0 ° and 3 5 ° but would be less effective i f the superstructure is damaged inboard of the casing line, also i f flooding takes place upwards via the stairways fiom the lower vehicle space. If a restricted damage height above the load waterline is considered, rather than damage upwards without limit, access openings protected by watertight doors in the superstructure and integrity of windows could be vital in delaying capsize after water has entered the main car deck after damage.
3.4 Intact Stability
The analysis referred to i n para 2.5 showed that trim i n service is normally between 0.5m by the stern and level keel. G Z curves for the load draft were produced for level keel, 1.0m stern trim and 0.50m bow trim and since it was found that the variadon i n G Z was small, and i n order to reduce computer dme and the amount of data to be processed, i t was decided to assume level keel and to invesdgate at the maximum load draft and an average load draft. These were run for three different values of K.G. giving the G Z curves shown in fig. 6. Since subsequent results for the various hull forms gave a similar spread of curves the results plotted for this report have been confined to the load condidon 2 in fig.6 which corresponds to a realistic maximum load condition.
To give a measure of the relative value of the hull up to main deck, between main and upper decks, and including the superstructure, G Z curves for all three are plotted i n fig.7. The next stage was to look in depth at the area between curves 1 and 2 to see the effect of subdividing the main vehicle space in different ways.
Figure 8 shows the same G Z curves for the total ship up to main and upper decks as in fig.7 with the addition of the following cases where parts of the vehicle space are open to the sea.
Curve A - H u l l to main deck + exisdng casings to upper deck.
Curve B - H u l l to main deck + modified casings to upper deck.
Curve D - H u l l to upper deck - space between Bhd 49 & Bhd 89.
The range of stability with modified longitudinal casings is seen to be the same as with transverse bulkheads but the former gives a better maximum G Z value.
Figure 9 shows the same curves but includes the added effect of the superstructure. For both m o d i f i e d casings and transverse bulkheads the i n c l u s i o n of the superstructure shows that instead-of rapid capsize after a heel of 3 5 ° is reached the ship will survive and increase G Z rapidly after 5 0 ° .
Water on Main Vehicle Deck
Water entering the vehicle deck, and remaining in sufficient quantity to affect stabihty, can be treated either as an additional weight with a free surface, or as lost buoyancy with the space concerned being open to the sea. Both have been investigated and G Z curves for the different ship arrangement are shown in fig.8 and fig.lO and 11. Figure 10 shows that 200 tonnes of water on the deck is sufficient to produce an angle of heel which that will immerse the deck edge.
Figure 11 shows that 400 tonnes of water on the vehicle deck produces a list of 16° and a range of stability of 3 5 ° compared with a range of 5 6 ° for the unflooded ship. Containing the water between transverse bulkheads without side casings produces a list of 14.5° and a similar range. With side casings and no bulkheads the list is 6 ° (sufficient to keep the deck above water) and the range is 4 7 ° .
Figure 8 shows the effect on the G Z curve of assuming that parts of the hull are open to the sea and do not contribute to righdng lever.
Water can enter the vehicle deck either through an opening in the sheU or as a result of fire fighting. I f there is an opening in the hull and water can flow i n and out without restriction, the space can be taken as open to the sea with stability reduced as in fig.8. I f however water enters the space faster than it can flow out the situation is more serious as the volume of water can increase until capsize occurs. This is also the situation i f water from fire fighting does not clear and no steps are taken to reduce the flow. I n this situation of a build up of floodwater, division of the vehicle deck is of value in reducing the effects of loose water, but will not of itself prevent capsize or founder if the supply of floodwater is unlimited.
Side casings are of value in preventing flooding of the vehicle space via a side opening, and transverse bulkheads are of value to limit flooding via a bow or stern opening.
3.6 Damaged Stability
Calculations have been carried out for the Ship No. 1 for two compartment flooding at a range of five drafts and four trims to give the G M values needed to satisfy the following criteria.
a) No margin hne immersion at any stage of flooding b) G M of 0.05m after flooding
c) Positive stabihty at all stages of flooding
d) Heel not to exceed 7 ° after asymmetric flooding.
From these values of G M , a curve was constructed to give the G M requirement to meet both intact and damaged stability criteria for the range of operating drafts.
For level keel, t r i m by the stern and trim by the bow the G Z curves after damage for the thirteen pairs of compartments are shown in flg.l2. I n the case of level keel, excluding the two curves for the forward end, all the other damage cases give a final range between 1 0 ° and 16° and a final maximum G Z between 0.04m and 0.12m. These figures are similar for 0.5m trim by the stern and 0.3m trim by the head. For this reason initially, only level keel initial drafts were considered. Following the pubhcation of the report of the Herald of Free Enterprise enquiry, all the damage cases were also run for trims of 1.0m by the stern and 0.5m by the bow.
Three cases of damage were selected.
a) Damage 56 flooding the first tunnel and the engine room since this gives the final G Z curve with the least range and the smallest maximum G Z value.
b) Damage 67 flooding the engine room and auxiliary machinery space since this gives the highest G M requirement to meet the criteria.
c) Damage 78 flooding the auxiliary machinery space and the alternator room since it includes the car deck bhd at fr.89 fltted to improve damages a) and b).
These three damage cases were run at three drafts with a fixed K G of 9.85m to give a range of initial freeboards and G M values, at level keel trim as follows.
Load Condition 1 D r a f t M i d . 5.00m G M .36ra Load Condition 2 Draft M i d . 4.72m G M 1.55m Load Condition 3 Draft M i d . 4.44m G M 1.74m
The three damage cases were given suffixes according to the assumed extent of flooding within the vehicle space as follows.
A l To upper ("B") deck with car space and casings flooded @ 95%.
A2 To upper ("B") deck with car space and casing l.W.O. damage flooded.
B l To upper ("B") deck with car space and modifled casing l.W.O. damage flooded.
B2 To upper ("B") deck with modified casing l.W.O. damage flooded.
C To upper ("B") deck with car space between bhds and modified casings l.W.O. damage flooded.
D To upper ("B") deck with car space between bhds flooded and no casings fitted.
In all the above cases allowance has been made for flooding up into the machinery casing.
The results at the Load Condidon for the three damage cases are given in figs. 13, 14 and 15.
Criteria for Residual Stability
For the three damage cases, (56, 67 and 78) the GMs required to meet criteria i n addition to those listed in the previous paragraph were determined. These additional criteria are listed in dg.l6a) and are based on proposals currently being discussed at I M G . The application of all the criteria to damage case 56 is also shown in fig.l6b) and c) and d) for three alternative geometries.
Figs. 12 a), b) and c) show, for Ship 1 'as built', four damages fall well short of the highest proposed (.10m G Z residual) criteria, seven damages are close to meedng both the residual G Z and range criteria and the remaining damages (at ends) comfortably meet the criteria.
Figs. 16 a), b) c) and d) confirm that a combinadon of higher residual G M and increased freeboard would be necessary to meet the highest proposed crheria with otherwise existing geometry, however a combination of increased beam with reduced length of cridcal compartments in addition to increased freeboard would be necessary. The influence of heightened K G on intact stability requirement is likely to be critical but has not been investigated fully. Shortening of critical compartments would also affect machinery arrangements signiflcantly and would probably influence selecdon of main propulsion machinery.
In addidon to calculations for Ship 1, limited calculations (not reported) are available for a second R o / R o passenger ferry which demonstrate that acheivement of the highest proposed residual stability criteria under consideration at I M G would be virtually impracticable. Any conclusion which might be drawn from the results of the investigation of Ship 1 must therefore recognise the limited extent of the invesdgations carried out. Further work is needed to evaluate the induence of new criteria on a variety of ship configurations.
SECTION 4
CAPSIZE SITUATIONS
!
CAPSIZE SITUATIONS
A n analysis of Lloyds Registers statistical evidence to the Zeebrugge disaster inquiry, also preliminary discussions with Lloyds Register aimed at identifying areas for interacdon between Tasks 1 and 3 suggested that concentration on the consequences of side damage would result in an incomplete and inadequate assessment of the overall safety of Ro-Ro vessels. See also the report of Task 3.
This confirms the views expressed by the Department of Transport in discussions during the compilation of this research programme.
The above analysis also points to capsize often being due to the secondary effects of primary incidents many o f w h i c h are due to reasons other than contact or collision.
The influence of ship geometry on survival following various types of primary incidents other than collision or contact has been investigated including grounding, fire and explosion, cargo shift and steering, with the following observations
:-i) Grounding
Up-flooding following bottom damage and leading to foundering rather than capsize is the most likely consequence i n extreme cases.
The possibility of up-flooding f r o m tanks below the bulkhead deck via air pipes or piping fitted for down-flooding of vehicle deck areas has to be considered. A i r pipes led outboard rather than into vehicle deck spaces and non-return or shut off valves in down-flooding piping will obviate problems. Reserve buoyancy provided by intact freeboard is obviously of primary importance.
ii) Fire and Explosion
In addition to the well known problems associated with the use of large quantities of water to extinguish fire in passenger ships, the operation of drencher systems on vehicle decks must be considered.
-It is standard pracdce for drencher systems to be fully tested, with the pump working at f u ü capacity and with fire hoses additionally discharging into the vehicle deck space. Drainage overboard is normally effected by gravity via ship side scuppers.
Rate of supply of water is normally in the order of 5 tonnes per minute and equilibrium between supply of water and drainage overboard is achieved in a few minutes by which time angles of heel of the order of 2 degrees are experienced with modest quantites of water forming a shallow wedge on the vehicle deck.
The availability of sufficient intact freeboard to provide a positive head at the scuppers, also maintenance of clear scuppers free from obstruction are of vital importance.
The supply of water to the vehicle deck is however fully under control and rate of application is low. Substantial time will elapse before, in the event of inadequate drainage, angles of heel sufdciently large to prejudice either the intact stabüity of the vessel or ability to launch LSA could occur.
The effects of the modest quantities of water on deck in a dynamic situadon in adverse weather are not fully known, tank tests proposed in Task 4 will provide more information.
Subdivision of vehicle decks by internal bulkheads (full or partial height) would reduce dangers of large free surface but would complicate drainage and drencher system piping arrangements. Longitudinal bulkheads could in some circumstances produce larger heeling moments than with open vehicle decks. The presence of subdividing bulkheads would also inhibit access for inspection of vehicles and f i r e f i g h t i n g , also complicate v e n t i l a t i o n arrangements essential for the maintenance of an explosive mixture free and toxicity free atmosphere.
iii) Shiift of Cargo
The primary effects of shift of cargo, including possible vehicle turnover, should be resisted by the vessel's available righting moment, however secondary effects may include fire and explosion and possibility damage to structure or to closures of vehicle deck openings.
Secondary effects of other incidents involving large angles of heel would lead to possible vehicle overturns or load shedding.
Transverse bulkheads could provide additional protection to openings whilst longitudinal sub-division would inhibit transverse movement of vehicles or their loads if shed.
iv) Steering Problems
Passenger Ro-Ro vessels are usually designed for high speed and are invariably highly manoeuvrable. Angle of heel during turn under emergency condidons is demonstrated during builders trials, however in adverse service condidons vessels with inadequate intact stability characteristics could well experience load shedding or possible vehicle overturns when the comments in ni) above apply. No investigation of this possible problem area has been made in the work of Task 1.
v) Openings To Vehicle Decks
The effectiveness of the buoyancy of the vehicle deck superstructure is primarily dependent upon the height above water of the sills of end or side openings, also the efficiency of the closing appliances.
Leakage via defective closures can, in most circumstances be dealt with via drainage arrangements whether by gravity or pumping.
Major failures of closing apphances can be countered using one or more of the following geometries investigated.
a) Provision of adequate intact freeboards to prevent ingress of water in catastrophic quantides.
b) Duplication of closing appliances particularly forward.
c) Internal subdivision of the vehicle space.
Amount of freeboard is usually related to the level of watertight subdivision (compartmentation standard) achieved below the bulkhead deck, sheer forward and aft being an important feature. Freeboard to some vessels vehicle decks openings is also designed to meet possible limitations at terminal facilides although in most U K vessels these limitations tend to mitigate against exceptionally low freeboards at the ends of vessels.
SECTION 5
VEHICLE DECK ARRANGEMENTS
5.1 I n addition to tlie arrangements of longitudinal and tranverse bulkheads examined in Section 3, many suggestions for the improvement of R o / R o vehicle deck arrangements have been examined, which include
:-i) Subdivision of the vehicle space by a) hinging transverse bulkheads b) flexible transverse bulkheads
c) vertically folding transverse bulkheads
d) longitudinal partial bulkheads or coamings sometimes linked with folding partial transverse bulkheads.
ii) Downflooding to centre tanks.
iii) Downflooding to achieve heel away f r o m damage.
iv) Double skin vehicle decks of cellular construction draining water entering the space with complex downflooding.
5.2 The possible value of partial bulkheads or coamings has not been fully assessed but improvement i n survival capacity can be judged f r o m the results of computations in Section 3 for f u l l height divisions. The range of effectiveness can be estimated by reference to the angle of heel at which water would overlap such divisions.
5.3 The geometries investigated in Section 3 envisage the use of hinging transverse bulkheads to achieve transverse subdivision, however it is apparent f r o m Appendbc 1 that whilst such arrangements could be practicable in Ships 1, 2, 4 and 6, the breadth of vehicle deck to be closed off would lead to considerable practical difflculties in Ships 3, 5, 7, 8 and 9. The geometry of new ship designs might be better arranged to minimise such practical problems.
5.4 Loss of vehicle stowage resulting f r o m arrangments considered in 5.2 and 5.3 has not been fully evaluated; however three transverse divisions would be required in any effective vehicle deck subdivision.
5.5 The merits of downflooding and gravity discharge overboard of floodwater have been examined. Whilst the angle of heel at which the deck edge will be immersed is an important consideration (and associated with initial freeboard) it would seem that reliance upon gravity discharge alone, given adequate intact freeboard, is inferior to a system which also provides an additional facility to pump overboard from drain tanks.
5.6 Prevendon of involuntary downflooding via access openings to spaces below the bulkhead deck needs further study. Suggestions that such openings should be prohibited would remove damage control options which have been useful in avoiding rapid capsize i n several known casualties. Development of a design of a lower category watertight door for such openings and which also meets fire regulations would contribute to providing design options.
5.7 Downflooding i n most situations, intact or damaged will lead to reduction of freeboard, hence enhancing opportunites for additional floodwater to enter the vehicle space. Ingress of large quantites of water must, it would seem, be avoided by design or controUed i n other ways. Ingress of smaUer quantites of water can be dealt with by overboard gravity discharge, however for intermediate quantites the comments i n 5.5 are appropriate.
5.8 Arrangements examined which are aimed at transferring floodwater entering the vehicle deck after damage to tanks on the intact side have been found to present problems when all potential damage situations are considered.
Systems incorporating tanks fitted above the vehicle deck and which discharge overboard in the event of side damage thus inducing heel to the intact side, are worthy of further study. Vulnerable areas of potential side damage can be fitted with such tanks which would automatically provide improved freeboard in way of damage but at some cost in structure, loss of useable space and loss of payload. See figure 17a) for iUustration of this principle.
5.9 Whilst limited longitudinal bulkhead arrangements have been investigated in Section 3, it is clear that the worth of all double skin arrangements is dependent upon the hkelihood of their being pierced by damage, also by the spacing of .dividing transverse bulkheads within the double skin.
The possibihty of water entrainment within double skins contributing to heel towards damage i n dynamic situations needs to be further investigated.
Full evaluadon of benefits after side damage will be possible only after updating of damage statistics and on completion of Task 4.
There is no doubt however that i n many circumstances leading to the presence of water on vehicle decks longitudinal subdivision wiU reduce free surface and wedge effects.
5.10 One geometry which wordd seem to resolve most water on vehicle deck problems is the arrangement of a longitudinal recess along the length of the vehicle deck. Figure 17b) shows possible configurations which illustrate the two principal benefits, increased freeboard at sides and an ability to contain substantial quantities of floodwater whilst lowering V C G and limiting free water effects.
SECTION 6
6. SURVIVAL PREDICTIONS
I M O Resolution A265 ( V I I I ) provides a logical method for comparing survival capabilities of passenger vessels after damage using probabilistic methods.
Whdst the work of Task 4, the improvement of damage extent statistical data and studies proposing refinements to A265 will contribute to greater confidence in the method, it would seem essential that in the evaluation of overall risk, consideration be given to "non-surviving" cases.
In particular the likely incidence of rapid or slower capsize after "non-survival" events needs to be examined.
Meaningful comparisons of the benefits of new or revised geometries above and below the bulkhead deck can, it is proposed, be made using an extension to the A265 calculation.
The foUowing method is suggested as a useful comparative computation.
i) Calculate a p s values for vessel below bulkhead deck.
ii) For each compartment group assume
:-a) Any damage producing an 'S' value of 1.0 survives.
b) Any damage producing an 'S' value below 0.5 should be regarded as a potential rapid capsize (for ap-aps).
c) Any damage producing an 'S' value between 0.5 and 1.0 should be regarded as a potential slower capsize (for ap-aps).
iii) Recalculate as for ii) taking into account improvements in 'S' values resulting f r o m vehicle deck subdivision.
(It is assumed that no allowance is given for the buoyancy of superstructures at higher levels, i.e. buoyancy becoming effective at angles of heel exceeding say 30 degrees).
This method has been applied to Ship No. 1 as built and with arrangement of longitudinal bulkheads on the vehicle deck. The results are shown at Appendix 2.
SECTION 7
DISCUSSION
7. DISCUSSION
7.1 The widening of the area under investigation from consideration only of residual standards of stabihty after damage to a more general study of ship geometry, particularly above the level of the vehicle (bulkhead) deck has limited (in the time available) the consideration of the effects of variations in intact freeboard and stability on survival capability as expressed in terms of residual G Z and range.
7.2 Interaction between work on Tasks 1 and 3 has however highlighted the need to consider the influence of ship geometry both above and below the bulkhead deck on overaU ship safety assessment. I n particular the influence of intact ship freeboard in avoiding potential ship capsize or founder situations which might arise either f r o m side damages or other situations in which the basic buoyancy or stability of the vessel may be prejudiced, is seen to be of prime importance. In other words the level of the platform to which the fundamental watertight integrity of a vessel is maintained is the most important feature in
i) preventing and resisting ingress of water above the bulkhead deck level in "undamaged" conditions.
ii) providing adequate reserves of buoyancy in damaged conditions.
It can of course be argued that in meeting requirements for damaged situations, all other potential situations will be covered, however the likely frequency of occurrence of all other potential capsize or foundering situations should be taken into account and given appropriate weight in assessing overall safety levels. Further studies of such an assessment are to be recommended.
7.3 The value of subdivision above the vehicle (bulkhead) deck has been quantified in terms of improvement in G Z curves for arrangements in which transverse and longitudinal bulkheads in various combinations have been investigated. Whilst only one basic ship f o r m has been studied (due to time constraints) it is considered that general conclusions can be drawn f r o m the
improvement is obtained, however the benefits are considerably reduced in the event of damage involving any one of these bulkheads.
ii) With longitudinal bulkhead arrangements survival capability is enhanced more than with transverse bulkheads provided that the inner skin is not pierced by a damage. Spacing of transverse bulkheads between ship side and longitudinal bulkheads will depend upon the pracdcal use to which the space is put but even with transverse subdivision at distances compatible with use for vehicles the results indicate superiority of this arrangement over that with side to side transverse bulkheads only. Closer spacing of transverse subdividing bulkheads w i t h i n side casings w o u l d produce f u r t h e r improvement however use of the space would be restricted.
iii) Arrangements of subdividing bulkheads above the bulkhead deck become effective only after immersion of the margin (or flooding limit) line. Changes in regulations, which presently prohibit immersion of a vehicle deck, wiU be necessary to give credit for the value of intact buoyancy above this level i n both intermediate and final stages of flooding.
7.4 The presence of superstructures at high levels above vehicle spaces and their value in resisting rapid capsize needs further study. Some of the vessels examined have htde useful reserve buoyancy at higher levels but most would seem to have the capability of retarding vessel overturn although large angles (30 degrees plus) of e q u i l i b r i u m w o u l d result. V e r t i c a l extent of assumed damage, i n t e r n a l arrangements, upflooding and strength of windows would affect the time during which this reserve of buoyancy would remain effective. The possibility of shift of vehicles and cargo also the effectiveness of ship abandonment arrangements need to be considered. Nevertheless such temporary reserve buoyancy could well be invaluable in potential capsize situations.
7.5 A large number of suggestions for improved vehicle deck internal arrangements were found to be impracticable for a variety of reasons, however several are worthy of further study. It is perhaps appropriate to record that the benefits of some potentially worthwhile arrangements or devices may not be of a nature that can be easily be given credit in existing reguladons which virtually ignore arrangements above the bulkhead deck in vehicle ferries.
7.6 One over-riding problem in any assessment of the benefits of new or revised geometries above or below the bulkhead deck or i n comparing alternatives is the limited knowledge of conditions likely to cause capsize. It is suggested that the informadon contained i n A265 and its explanatory notes can be used (until better information becomes available) f o r comparative purposes using the method suggested in the report.
The work proposed in Task 4 wiU contributed significantly to an improvement of knowledge in this area as will the accumulation and analysis of more up to date damage statistics, particularly for penetration of damage.
7.7 Whilst computations have been made for one basic ship only, an assessment can be made from the results of the likely consequences on ship design of various proposals for residual standards of stabüity. Results f r o m Task 4 will also enable a more reahstic assessment of required standards to be made.
7.8 The influence of irdtial trim on residual standards of stability was, for the basic ship, found to be relatively unimportant. This is no doubt due to the particular geometry of Ship 1, however i n future designs it would not seem too difficult to arrange suitable bulkhead spacings forward and aft, combined with appropriate sheer profiles, to avoid limitation of normal service trims.
S H I P N O . I L . B . P . = 120.70m DEPTH TO MAIN V E H , DK. = 6.40m DRAFT = 5.00m FREEBOARD = I.40m
—
—
Ü
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V S H I P N O . 4 L . B .P . = 119.50mDEPTH TO MAIN VEH. DK. = 7.60m
DRAFT = S.IBm FREEBOARD = 2.42m ^ / / / / / T'7y~/y /
/ / / / v
'\ V V / / / / / / / / ' / >i !''yW/\
/ / / / / /v_
1
V . S H I P N C . y L . B . p . = 122.B5m DEPTH TO MAIN V E H . DK. = 5.30m DRAFT = 5.03m FREEBOARD = 1.27m S H I P N O . 2 L . B . P . = I I 0 . 2 1 n DEPTH TO MAIN V E H . DK. DRAFT = 4 . I 2m FREEBOARD = 2 . 0 5 S H I P N O . 3 L . B . P . = 1 l 9 . S 0 m DEPTH TO MAIN V E H . DK. = DRAFT = 4.57m FREEBOARD = I . 9 8 m ' / / / / / /:> ////<:
\ / / / / / / 'z V)
V)
S H I P L . B . P . = NO. e 159.BOm DEPTH TO MAIN V E H . DK. = 7.OSmDRAFT = 6 . I 3 m i
;r
-//v
/y/
/ / / / / / / /V
)
S H I P N O . 9 L . B . P . = 138.00m DEPTH TO MAIN V E H . DK. = 7.60inDRAFT = 6.22m FREEBOARD = 1 .38m
ARRANGEMENT OF S H I P I
F I G .SHIP I - VARIATIONS I N LONGITUDINAL CASINGS & TRANSVERSE BULKHEADS ON MAIN VEHICLE DECK
DAMAGE DAMASE DAMA3E P O S N . P O S N . P O S N .
5 6 5 7 7 8
P 10 Ï 0 -TO *0 50 «0 70 eo 00 100 110 120 130 1*0 ISO JOO
E X I S T I N G
DAMAGE DAMAGE DAMAGE P O S N . P O S N . P O S N .
5 6 6 7 78
M O D I F I E D C A S I N G S
DAMAGE DAMAGE DAMAGE P O S N . P O S N . P O S N . 5 6 5 7 78 — 1 1—1 - T — 1 — . . ) .10 *0 ij 00 7 ^ " ao io 100 tlo Tzo 1 . 1 — 0 K O 1 M O D I F I E D C A S I N G S i Ü U L K H E A D S
DAMAGE DAMAGE DAMAGE P O S N . P O S N . P O S N . 5 6 67 7 8
d 1
\
•
- IC 0 10 20 SO +0 iO OO 70 SO >o 100 no 120 1 10 jlo IiL] 1
T R A N S V E R S E B U L K H E A D S jotr_Deo< SUPERSTRUCTURE M I D S H I P S E C T I O N SUPERSTRUCTURE M I D S H I P S E C T I O N SUPERSTRUCTURE BULKHEAD M I D S H I P ' S E C T I O N SUPERSTRUCTURE J_lt«E_=ECX BULKHEAD M I D S H I P S E C T I O N
F I G . 5 ( a )
S H I P I - V A R I A T I O N I N DRAFT d T R I M
F I G . 5 ( b )
S H I P I - V A R I A T I O N I N DRAFT & TRIM
F I G . 4
S H I P I - D I S T R I B U T I O N OF DRAFT
2 0 . I 8 _ I 6 _ I 4-. 1 2 . 1 0 . 8 _ 6 . 4 . 2 .r
M A X . D R A F T 5 . 0 1 m 4 . 5 - 4 . 5 9 ' 4 . 6 - 4 . 6 9 U . 7 - 4 - . 7 9 ' 4 . 8 - 4 - . 89 U . 9-4-. 9 9 ' 5 . 0 - 5 . 0 1 M E A N D R A F T ( M E T R E S ) 4 . 6 5 8 m S U M M E R 4 . 7 4 - 1 W I N T E R 4-. 7 0 0 m M E A NS H I P I
D I S T R I B U T I O N OF PASSENGER NUMBERS
F I G . 5
AGAINST DRAFT
NO. OF PASSENGERS 1400 1300 1200 I 100 1000 900 800 700 600 500 400 300 200 100 (gr ® X XMAX. NO. OF PASSENGERS
X 0 X X X X X X X
MEAN / FULL YEAR B A S I S
X X X X X X X ^ I E O iri 4.6 4.7 4 . 8 4.9 5.0
MEAN DRAFT (METRES)
X WINTER
S H I P I - GZ CURVES FOR INTACT S H I P WITH
V A R I A T I O N S OF DRAFT d GM
F I G . 7
S H I P I - GZ CURVES AT LOAD DRAFT
S H I P I
F'
I G . 10
S H I P I - WATER ON V E H I C L E DECK
o . a GZ ( M e t r e s ) 0 . 7MAIN DECK UNq)ER AT 7 . B DEG
MAIN DECK AT 7 . 5 DEG
CURVE NO. DRAFT D I S P L TRIM GM NOTE
1 5 . 0 1 7 m 7 7 8 2 1 0 1.250m LOAD DEPARTURE 2 5 . 0 6 9 m 7 8 8 2 1 + 0 . 0 5 m 1.354m l o o t WATER 3 5 . 1 1 8 m 7 9 8 2 1 + 0 . l O m 1.361m 2 0 0t WATER 4 5 . 2 I B m 8 l 8 2 t + 0 . 2 0 m 1.369m 4 0 0t WATER 5 5 . 4 1 3 m 8 5 8 2 1 + 0 . 3 5 m 1.371m 8 0 0t WATER
S H I P I F I G . I I
GZ CURVES W I T H 4 0 0 T OF WATER ON VEHICLE DK.
S H I P NO.
I
SUMMARY OF TWO COMPARTMENT DAMAGES
AT S U B D I V I S I O N DRAFT ( 5 . 0 METRES)
C 0 M P T 5 . F L O O D E D L E N G T H -3 . 5 m T R I M L E V E L K E E L 0 . 3 m T R I M C 0 M P T 5 . F L O O D E D L E N G T H GM TF / B O A R D H E E L ° GM F / B O A R D H E E L ° GM F / B O A R D H E E L ° 1 2 1 6 . 8 m 0 . 6 8 m 1 0 3 m 0 0 0 0 . 7 8 m 1 . 1 5 m 0 . 0 0 0 8 2 m 1 . 2 0 m 0 0 0 2 3 i 6 2 m 0 . 3 6 m 1 . 3 0 m 0 0 0 . 3 4 m 1 . 3 7 m 0 . 0 0 0 6 2 m 1 . 3 8 m 0 0 0 3 4 1 9 7 m 0 . 4 1 m 0 9 4 m 0 0 0 0 . 4 6 m 0 . 9 9 m 0 . 0 0 0 4 9 m 1 . 0''3m 0 0 0 4 5 1 8 9 m 0 . 5 2 m 0 . 6 5 m 0 0 1 0 . 5 8 m 0 . 7 6 m 0 . 0 0 0 6 1 m 0 . 7 9 m 0 0 0 5 6 2 1 Om 0 . 5 4 m 0 5 4 m 0 0 1 0 . 5 9 m 0 . 5 9 m 0 . 0 0 0 6 3 m 0 . 6 2 m 0 0 0 6 7 2 1 Om 0 . 5 4 m 0 5 8 m 0 0 0 0 . 6 2 m 0 . 6 2 m 0 . 0 0 0 6 6 m 0 . 6 4 m 0 0 0 7 8 1 7 5 m 0 . 8 2 m 0 6 4 m 0 4 8 0 . 7 7 m 0 . 6 4 m 0 . 4 2 0 7 3 m 0 . 6 4 m 0 3 9 8 9 1 7 5 m 0 . 9 5 m 0 5 2 m 5 9 0 . 8 8 m 0 . 5 2 m 0 . 5 1 0 8 4 m 0 . 5 2 m 0 4 8 9 1 0 1 4 . Om 0 . 9 3 m 0 4 9 m 1 2 6 0 . 9 7 m 0 - 4 9 m 1 . 2 0 0 9 9 m 0 . 5;3m 0 9 1 1 0 1 1 1 4 . Om 1 . 0 5 m 0 7 3 m 0 0 2 1 . 0 7 m 0 . 7 1 m 0 . 0 0 1 0 8 m 0 . 6 5 m 0 0 0 1 1 1 2 1 4 7 m .1 . I 5 m 0 8 1 m 0 0 2 1 . 1 4 m 0 . 7 8 m 0 . 0 2 1 1 4 m 0 . 6 7 m 0 0 1 12 13 1 2 7 m 1 . 2 8 m 1 0 7 m 0 0 3 1 . 2 6 m 1 . 0 4 m 0 . 0 2 1 2 5 m 1 . 0 2 m 0 0 2 13 14 1 2 8 m 1 . 4 7 m 1 1 Om 0 0 1 1 . 4 6 m 1 . 0 7 m 0 . 0 0 1 4 5 m 1 . 0 4 m 0 0 1F I G . 1 3 ( a )
S H I P N O . I
F I G . 1 3 ( b )
S H I P N O . I
DAMAGE CASE 5 6 - V A R I A T I O N OF DRAFT
0 . 5 GZ ( M e t r e s ) 0 . 4 CONDITION DRAFT D I S P L . GM 5 5 . 0 0 m 7 7 8 2 T 1 .36m I I 4 . 7 2 m 7 I 9 0 T 1 .55m 14 4 . 4 4 m 661 1 T 1 . 74m
0 . 5 GZ ( M e t r e s ) 0 . 4
S H I P NO.
F I G . 1 3 ( c )
DAMAGE CASE 5 6 - V A R I A T I O N OF TRIM
CONDITION TRIM D I S P L . GM 2 1.Om STERN 7 9 6 0 T 1 .32m 5 NO TRIM 7 7 8 2 T 1 .36m 8 0 . 5 m BOW 7 7 0 IT 1 .34m
S H I P N O . I
DAMAGE CASE 5 6 - V A R I A T I O N OF KG
F I G . 1 3 ( d )
0 . 5 GZ ( M e t r e s ) 0 . 4 CONDITION KG D I S P L . GM 4 10 . 0 5 m 77B2T 1 . 16m 5 9 . 85m TT 1 . 36m 6 9 . 65m 65m n 1 .56m 1 .56m 0 . 3 NO TRIM i DRAFT = 5 . 0 0 m \ 0 . 2 _l 0 . I n 1 6 0 7 b HEEL ! ( D e g r e e s ! ) - 0 . I - 0 . 2 - 0 . 3 - 0 . 4 i - 0 . 5 - 0 . 6 J _ - 0 . 7 \ JS H I P N O . I —
DAMAGE CASE 6 7 ( E . R . d AUXY. MACHY. FLOODED)
F I G .
S H I P N O . I
F I G . 1 6 ( a )
GMS REQUIRED TO MEET RESIDUAL S T A B I L I T Y C R I T E R I A
FOR VARYING DRAFTS AND TRIMS
C R I T E R I A
1. F I N A L GM 0 . 0 5 m
2 . MARGIN L I N E NOT IMMERSED AT ANY S T A G E .
3 . F I N A L MAX. GZ 0 . 0 5 m OVER RANGE UP TO 7 D E G , 4 . F I N A L RANGE OF S T A B I L I T Y OF 7 D E G .
5 . F I N A L AREA UNDER GZ CURVE 0 . 0 0 3 M RADS.
6 . F I N A L MAX. GZ 0 . I O m OVER RANGE UP TO 15 D E G . 7 . F I N A L RANGE OF S T A B I L I T Y OF 15 D E G .
B . F I N A L AREA UNDER GZ CURVE 0 . 0 2 0 M RADS.
9 . GZ 0 . 0 3 m OVER RANGE UP TO 5 D E G . AT A L L S T A G E S . 10. RANGE OF 5 D E G . AT A L L S T A G E S .
DAMAGE CASE 5 6 A I
(TOTAL CAR DECK AND E X I S T I N G CASINGS FLOODED)
GM REQUIREMENTS
DRAFT 5 . OOM 4 . 7 2 M 4 . 4 4 M TRIM - 1 . 0 + 0 . 5 - 1 . 0 0 + 0 . 5 - 1 . 0 0 + 0 . 5 C R I T E R I A 1 0 . B4 0 . B 8 0 . 79 1 . 0 8 0 . 9 5 0 . 9 4 1 . 0 9 0 . 9 0 0 . 8 7 2 1 . 2 3 1 . 2 0 1 . 1 8 1 . 3 4 1 . 3 3 1 . 2 8 1 . 2 8 1 . 4 4 1 . 3 6 1 . 3 6 3 1 . 6 2 1 . 4 5 1 . 1 8 1 . 3 4 1 . 4 7 1 . 3 4 1 . 3 3 1 . 4 8 1 . 2 9 1 . 2 9 4 1 . 2 4 1 . 0 5 0 . 9 4 1.14 1 . 0 6 0 . 9 3 0 . 9 2 1 . 0 7 0 . 8 8 0 . 8 8 5 1 .41 1 . 2 5 0 . 9 4 1.14 1 . 2 8 1 . 1 4 1 . 1 3 1 . 2 8 1 . 0 9 1 . 0 8 6 2 . 0 5 1 . 8 6 1 . 75 1 . 8 3 1 . 6 9 1 . 6 8 1 . 7 9 1 . 5 9 1 . 5 9 7 2 . 3 2 2 . 0 4 1 . 93 1 . 9 7 1 . 6 9 1 . 6 7 1 . 7 2 1 . 4 8 1 . 4 7 B 2 . 2 6 2 . 0 1 1 . 8 9 1 . 9 8 1 . 7 9 1 . 7 8 1 . 8 7 1 . 6 6 1 . 6 5DAMAGE CASE 5 6 B I
( M O D I F I E D S I D E CASINGS DAMAGED)
GM REQUIREMENTS
DRAFT 5 . OOM 4 . 7 2 M 4 . 4 4 M TRIM - 1 . 0 0 + 0 . 5 - 1 . 0 0 + 0 . 5 - 1 . 0 + 0 . 5 C R I T E R I A 1 0 . 78 0 . 8 7 0 . 7 8 1 . 0 6 0 . 9 4 0 . 9 3 1 . 0 9 0 . 9 0 0 . 8 8 2 1 . 2 3 1 . 1 9 1 . 1 8 1 . 3 3 1 . 2 8 1 . 2 8 1 . 4 4 1 . 3 6 1 . 3 6 3 1 . 4 5 1 . 3 3 1 . 2 2 1 . 4 4 1 . 2 9 1 . 2 8 1 . 4 8 1 . 2 9 1 . 2 8 4 1 . 0 5 0 . 9 2 0 . 8 1 1 . 0 3 0 . 8 8 0 . 8 7 1 . 0 7 0 . 8 8 0 . 8 7 5 1.21 1 . 0 6 0 . 9 8 1 . 2 0 1 . 0 4 1 . 0 3 1 . 2 3 1 . 0 6 1 . 0 5 6 1 . 6 8 1 . 5 0 1 . 4 3 1 . 6 3 1 . 4 8 1 . 4 7 1 . 6 6 1 . 4 9 1 . 4 8 7 1 . 3 2 1 . 14 1 . 0 5 1 . 2 5 1 . 10 1 . 0 9 1 . 2 9 I . I I 1 . 10 8 1 . 5 6 1 . 4 2 1 . 3 4 1 . 5 3 I . 3 8 1 . 3 7 1 . 5 7 1 . 3 9 1 . 3 8 9 1 . 5 9 1 . 5 8 I . 5 7 1 . 6 8 1 . 6 7 1 . 6 7 1 . 7 9 1 . 7 4 1 . 7 4 . 10 1 .01 0 . 8 7 0 . 7 7 0 . 9 9 0 . B 6 0 . 8 5 1 . 0 3 0 . 8 5 0 . 8 5DAMAGE CASE 5 6 D
( W I T H BULKHEADS ON CAR DECK)
GM REQUIREMENTS
DRAFT 5 . OOM 4 . 7 2 M 4 . 4 4 M TRIM - 1 . 0 0 + 0 . 5 - 1 . 0 0 + 0 . 5 - 1 . 0 0 + 0 . 5 C R I T E R I A 1 0 . 79 0 . 8 7 0 . 78 1 . 0 6 0 . 9 3 0 . 9 3 1 . 0 9 0 . 9 0 0 . 8 9 2 1 . 2 3 1 . 1 9 1 . 1 8 1 . 3 3 1 . 2 8 1 . 2 7 1 . 4 4 1 . 3 6 1 . 36 3 1 . 4 5 1 . 3 2 1 . 2 2 1 . 4 4 1 . 2 9 1 . 2 8 1 . 4 8 1 . 2 9 1 . 2 8 4 1 . 0 4 0 . 9 1 0 . 8 1 1 . 0 3 0 . 8 8 0 . 8 7 1 . 0 7 0 . 8 8 0 . 8 7 5 1 . 0 3 1 .01 0 . 9 4 1 . 1 5 1 . 0 3 1 . 0 2 1 . 2 3 1 . 0 5 1 . 0 5 6 1.41 1 . 36 1 .31 1 .51 1 . 4 2 1 . 4 ! 1 . 6 3 1 . 4 7 1 . 4 6 7 1 . 0 2 0 . 9 8 0 . 9 3 1 . 1 2 1 . 0 3 1 . 0 3 1 . 2 4 1 . 0 9 1 . 0 8 8 1 . 10 1.11 1 . 0 8 1 . 2 6 1 . 2 0 1 . 2 0 1 . 4 2 1 . 2 9 1 . 2 8 9 1 . 5 9 1 . 5 8 1 . 57 1 . 6 8 1 . 6 6 1 . 6 6 1 . 7 9 1 . 7 4 1 . 7 4 1 0 1 .01 0 . 8 7 0 . 7 7 0 . 9 9 0 . 8 5 0 . 8 5 1 . 0 5 0 . 8 5 0 . 8 5F I G . 1 7 ( a )
HEEL AWAY FROM DAMAGE
F I G . 1 7 ( b )
INCREASED FREEBOARD VCG DRAINAGE AND CONVENTIONAL DECKLINEAPPENDIX 2 SURVIVAL PREDICTION
1) C A L C U L A T E D ap V A L U E S (;A265')
For Sample Vessels
ap SHIP 1 1 2 3 COMPT COMPT COMPT .280 .382 .303 SHIP 2 1 2 3 C O M P T COMPT COMPT .322 .423 .255 SHIP 3 1 2 3 C O M P T COMPT COMPT .314 .441 .245 SHIP 4 1 2 3 C O M P T COMPT COMPT .297 .449 .254 SHIP 6 1 2 3 C O M P T COMPT C O M P T .303 .434 .263 SHIP 7 1 2 3 C O M P T C O M P T COMPT .304 .410 .286
The likely occurence of damage extent in Ship 1 is thus shown to be reasonably representative of the sample.
APPENDIX2
Full A265 calculations were performed at the time of build for a sister vessel similar to Ship 1. 'S' values (taking into account differences between the vessels) have been estimated for each compartment group and the resulting aps values are summarised below. ap a ^ non-surviving 1 compt .280 .280 .000 2 compt .382 .363 .019 3 compt .303 .092 .211 .965 .735 .230
For the vessel as built indices for survival and capsize were estimated to be
:-surviving slower rapid damages capsize capsize
1 compt .280 .000 .000
2 compt .363 .019 .000
3 compt .092 .105 .106
.735 .124 .106
The influence of adding longitudinal subdivision of the vehicle deck was then approximated. Full calculations of aps values for damage above and below the bulkhead deck have not been made, however taking into account likely penetration of damage and likely longitudinal extent and position of damage it is estimated
that:-i) all two compartment damage situations will now survive
ii) half of the three compartment slower capsizes will now survive
iii) one third of the potential rapid capsizes will be decelerated.
Survival and capsize indices then become
:-surviving slower rapid damages capsize capsize
1 compt .280 .000 .000
2 compt .382 .000 .000
3 compt .143 .087 .071
.805 .087 .071
5) I t is emphasised that the above calculation is intended only to be indicative of a proposed method, also that the indices resulting are intended primarily for a comparative assessment.
