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PAPER NO.8.

BUOYANCY IN THE WINGS

by E. Vossnack,

Naval

Architect.

Paper Presented at the

Kummerman International Conference on

RO-RO SAFETY AND VULNERABILITY: THE WAY AHEAD

Recent accidents with Ro-Ro passenger ships

show rapid capsizing;

-

Current methods to assess damage stability

are inadequate;

-

In this

paper

possible

improvements

on

existing ferries and new designs are described

to

obtain

a

higher

standard

of

safety.

3-1 QUESTIONABLE DAMAGE STABILiTY:

EUROPEAN GATEWAY;

TRANSIENT ASSYMETRIC FLOODING (Spouge).

3-2 TYPE OF SUBDIVISION

PE R .\1 E ABILITY

INCREASING BUOYANCY IN SHIPS WINGS,

SIDE WALLS (D.K. Brown, Aston and Rydill).

3-3 HOW TO MEET FUTURE STANDARDS

PROPOSED BY 1MO SUB-COM. SEPT.

'87

LONDON. (JR. HANNAH)

IMPROVING EXISTING FERRIES - NEW DESIG N

3-4

HULL INTEGRITY, WATER ON CARDECK,

FINS

3-5 RAPID DISEMBARKATION: MES'

3-6 STABILITY CHECK, CARGO PROBLEMS,

PROCEDURES

3-7 STEERING - MANOEUVRING AT PORT

ARRIVAL IN STRONG WINDS.

HEELING IN SHARP TURN AT FULL SPEED

BY

A SUDDEN 'HARD OVER' RUDDER

3-I

Questionable Damage Stability Range

Ro-Ro passenger damage stability requirements for

pasenger

ships

according

to

the

SOLAS 1974

Convention,

including

the amendments,

should be

revised.

The British Department of Transport (1980) and The

Netherlands

Shipping

Inspection

(1983) improved

SOLAS by implying

extra

requirements:

Final

Stability

Arm > 0.05 m-Range 7° minimum.

Furthermore, during any stage of flooding the margin

line should not be immersed.

This

stability standard

is

applicable

to passenger

vessels and Ro-Ro passenger ships without making

any difference.

BUOYANCY iN THE WINGS

by E. Vossnack,

Naval Architect, The Netherlands.

However, it should be realised that both types are

behaving quite differently when struck by a flared

forebody with an extending bulb

underneath.

On the conventional passenger ship, when listing, the

bulkhead deck

often

comes

quite

near to the

waterline and when rolling in waves, flooding over

the bulkhead deck can easily occur.

However, the

flow of water entering is limited by fire bulkheads

and partitions between cabins.

F 3

On the Ro-Ro vessel there is no compartmentation in

the Ro-Ro space above the bulkhead deck, (which

normally extends over the full breadth), and in a few

minutes a large mass of water can move freely and

wildly over a large

surface of

this

vehicle deck.

The moment of inertia of the vessel's waterline

is

enormously

reduced and

rapid capsizing is likely

within a few minutes.

For this reason Ro-Ro vessels

should comply to a higher damage

stability

requirement.

In

view of

the increasing traffic density, and the

quite realistic probability of being hit at a partition

bulkhead, a 2 compartment standard for all Ro-Ro

vessels should apply.

Moreoer an alarming phenomenon

is

indicated b

Mr. Spouge in his 'Investigation of the Sinking of the

Ro-Ro Ferry EUROPEAN GATEWAY' (The

RINA Apr. '85,

The Naval

Architect,

March, '86), the

so-called

'Transient

Asymmetric

Flooding.

After being hit at her side by the bulb of SEASPEED

VANGUARD, a

mass of

water

entered

via the

bulb-hole which represented a wave front

moving

into the engine room. Equalising of the surface went

on quite slowly.

The dynamic character

of this

calamitous insult on the

ship's

stability

has been

underestimated.

The sloped surface (10-13°) caused a larger angle of

heel than would follow from the assumed standard

'static'

flooding

calculation.

This

complication

caused the side of the bulkhead deck to dip well

below

the

waterline

diminishing

the

moment of

inertia.

The flared bow of the SEASPEED VANGUARD had

holed

the

topside

of

the EUROPEAN GATEV AY

allowing water to enter freely.

Personally I

greatly

appreciate

this

thorough

investigation; for the first time attention has been

paid to the 'Dynamics of

Transient

Asymmetric

Flooding' which caused the unexpected immersion of

the bulkhead deck, followed by flooding of the Ro-Ro

space.

Further research on this subject

is urgently needed

and should be carried out on a large scale.

Scale errors on model testing are to be avoided. 3-2 Consequences on Type of StEdivision

Transverse Subdivision

Should flooding calculations be carried

out in the

future by application of

_{100 sloped masses of water}

entering during the first minutes? (MNI FLOOD C.ALC.) Longitudinal Subdivision P 12 13 14 In a vessel which is subdivided by continuous

longitudinal bulkheads (at B/5 from the ship sides)

the rate of overflow of the mass of water from the

port wing tank to the SB wing tank, via the

cross-over duct, plays a very important role in the

heeling of the vessel; ducts should be made as large as possible (2-3 frame spacings at least).

The Netherland Shipping Inspection requires a

maximum overflow time lapse of

1

minute in which

case this

asymmetric effect may be

disregarded.

Research on the rate of overflow should be carried

Out Ofl a large scale imitating all discontinuities and

sharp edges of the vessels cross-over duct, assuming several sizes of the hole in the damaged shell.

Permeabihtv

Current permeability figures appear to be unrealistic:

85%

for engine rooms

is

applied, however a more

likely

figure for engine compartments is 9D-959

In order

to minimise immersion and heeling

of a

vessel b

masses of water entering, it

is logical to

reduce

the permeability

of the flooded compart-ments, especially in the waterline.

Permanent buoyancy could be applied

in

the void

wing spaces by stowage of empty drums; this

idea,

according to Mr. D.K. Brown, was carried out on

merchant vessels sailing in convoys during World War

Il, by stowing empty oil drums in the sides of the

tween deck spaces at waterline level.

One of these ships HECTOR

was hit by 6 torpedoes and still took

several hours to sink.

Moreover the ship sank in

upright condition.

Permanent buoyancy should be developed and might improve Ro-Ro Passenger

vessels which are built

under the 196)

Rules and presently do not comply

with

the later 1980 Ständards of the British Department of Transport.

Polythene drums or balls seem to be suitable in the

void wing spaces because they cannot corrode and

can be

easily removed. (Many alternatives are

mentioned in the table of P 14

At any time the ship structure and appendages should

be accessible for inspection.

Considering the fire-hazard, the polythene drums are

to be kept at a safe distance from shell

_{plating and}

bulkheads, where outside repair welding is likely to

Occur.

Drums could be lashed

either

vertically

or hori-zontally, depending on location.

Polythene balls bundled in nets might also be _applied in narrow compartments, (collapse-safety because of natural form).

p 5

Steel drums are heavy, might

_{rust and will collapse}

at 6 metre water pressure.

_{However they might be}

suitable in the wings of engine compartments because of fire-hazard.

By proper stowage a permeability of 50-60% could be

achieved, and it is a challenge to all of us to find a

practical method of filling

the void spaces during

fitting

Out and local removal in case of repair. Loss of deadweight and costs of permanent buoyancy seem to be reasonable.

A much greater increase of damage stability

range can be achieved by surrounding the Ro-Ro space by a double hull: so-called Side Walls'. _{(Aston and Rydill,} The Naval

Architect,

April,

'87). P 18

-In case of a wall width of 0.13 8, the

_{moment of}

inertia of

the waterline

is doubled and the vessel could survive a completely flooded cardeck.

In case of application of side walls,

having about 8

ft.

'container-width' and filling these 'subdivided'

spaces by polythene drums, the vessel most probably

will survive a collision at her side.

The depth of impact will be reduced by the

more

resistant steel structure in the ship's side.

(On top

of the side walls a marine 'escape slide and raft'

can be accommodated to allow

for

a rapid disembarkation).

2

The Ro-Ro design of maximum hull safety is

characterised by continuous:

Longitudinal bulkheads at B/5 belo the bulkhead deck (without watertight doors). Void Wing tanks

filled

up with drums. Side walls around the Ro-Ro space.

Engineers could sail with watertight doors in

transverse E.R. bulkheads open' in order to be

capable of immediate action in case of fire,

short circuit or leakage.

Closing these watertight doors is no longer

a must within one minute' because engine compartments are protected b _{8/5 void wing tanks on both sides.}

6«il : I I I I I ¡ L I J I I I _I N

SUBDIVISION

ABOVE

AND BELOW BIJLKHEADDECK

'sss CARIeS 4__3?V0_ I

-at-/2

RORO-PA55 FERRY

I.s. 161.55 I.. 45.40 O 5760 HMM SEO Ts, 6.23 T Ars 106 <Ç/M5 - LS 52430 0W 3515 S1.SPL 15839 4.1, 7'

L0U54C.3 .SoQP5 PASS cs5o5

I I j I I 1

O,tO'

L_.L___.JL.J

L..JL..__JT__.. I BULk4'D DRC5 I PASS 0100 CREO 58 30.83

3

PA5SENER VS5EL

L - 16E - M L1 O 3645 3030 1070 7.30 Ts s 7 40 2gKG/ LS 30000 SS 1 SISAL 05.000 PROS 900 PASS SM' cREW _'0151.CREW _SOfT717 PASS

As 713050.1 TILt

PASS .4 s 0.80. 7550 0 s 135 W

PA5

PROGRS$IVE FLOODING IS PREVENTED

BY FIRE- BULKHEADS AND CABIN-PARTITIONS

NO SUDIVI5ION

ve, j,I £5 A 400 lINA/Roo 2.1140 85e.',?: 0* .1500 5W, ITJIOfl' 7=55 CBIIOS H 2410M S5LIIRANT5 '1 PA3$ CAOlOS

'n» AA2S oseeS K4 I4.4 M PASS CARAS I, MMC PsOS CA3'MS PASS Ones S FASS Loess ..IMc.lSpfl 6.2J pl

/5J°\

50sTIlt0

2

H 26'3 M = t5,SS M

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Sinking of the roro ferry "European Gateway"

Dec'82

iy

.R.

POUCE.

NAVAL

ARC1IITE.CT

MARC.H &

EXTRACT:

Maximum penetration of the bulbous bow was 2.Om from the side shell (22m from the line of moulded beam), al-though the 0.5m deep frames caused damage up tot 2.5 m inside the shelL

Maximum penetration of the upper

deck was 3.5m from the side shell

(4.Om from the line of moulded beamj.

The technical investigation

of the flooding

The object of the investigation of the flooding was to determine firstly what had caused the unusually rapid heeling and sinking, and secondly what, if any-U thing, could have been done to prevent,

It.

Traditional dama9ed stability calcu-$ations

The EUROPEAN GATEWAY complied, with the current UK statutory require-ments for subdivision of passenger vessels,

which implement SOLAS

1960. These effectively require a orte-compartment standard, where the ship will survive with any one compartment below the bulkhead deck flooded. The bulkhead deck for the EUROPEAN GA-TEWAY was the main vehicle deck, and the spaces above this deck are neglec-ted in the calculations since they are not required to be watertight, although they would

have provided some

buoyancy, especially in a rapid sinking.

Causes of the heeling

Traditional damaged stability calcula- Various possible causes of the obser-tions, which were used at the design ved heeling were considered at the In-stage lo check that the ship complied

vestigation, concentrating on those

with the rules, indicate that sinking

which may have 'started the process would initially have been on an even off, since once a list to starboard was keel (i.e. no listj, since the compari- achieved. water collecting on that side ments which flooded were symmetri- of the ship would help to continue the calaboutthecentreline,Thefree-su-fa- heeling. lt would certainly have requi-ce lo&s due to water spreading over the red a considerable moment to achieve

four compartments below the bulk-

this initial

list, since the EUROPEAN head deck would eventually have been GATEWAY's metacentric height before sufficient to give the ship a negaive the collision was 2.87 m, with free-sur-metacentric height (GM), which would face losses of 0.74 m. This would requi-have caused a sudden capsize, or at

reamomentofl2.OMNm,tocausea5

least a lurch to art angle of loll. This

list,and24.2MNmtommersethemain

does not agree with the available evi- vehicle deck (i.e. the lip of the hole abo-dence (figuur 13). which strongly indi- ve the waterline).

cates that the ship began to heel

imme-Transient asymmetric fIoodin9 diately after the collision, and that this

heel steadily increased, at least until

The generator room, which flooded

first, is a shallow 'U" shape, containing the ship grounded. A more detailed

the generator and numerous pumps, consideration of the floodìng is impos- _{pipes floorplates and pillars. The} da-sible using this approach of its omis- _{mage hole was on the starboard side,} sion of time dependency. The traditio-

_{extending for half the height of the}

nal approach is therefore unsuited to

_{compartment, while the only}

signifi-explain this rapid sinking.

cant

exits were the comparatively

small doors to the engine room (on the

centreline att) and to the stabiliser

room (on the forward port side). lt is li-kely that the many obstructions to the Probabilistic damaged stability cal. flow of water across this compartment

culations prevented the water audace becoming Although the probabilistic approach is level, which is the impiicit assumption Only a sophisticated application of a, in aditional damaged stability calcu-large number of traditional damaged lations.

stability calculations, and therefore In the initial stages, the wave was ob-containsthesamelaults,itdoesindica- served to move across the compari-te the general level of safety of the ves- ment like a wall. Subsequently, as wa-sel in terms of survival following tloo- ter poured ¡n at about 20 tonnes/sec on ding. the starboard side, a considerable gra-dient would probably have remained 'on the water surface, albeit badly

die-'torted by the turbulent flow and the

sloshing response to the ship's motion.' The EUROPEAN GATEWAY would not This effect could have caused heeling comply with the new probabilistic da- to starboard, decaying from the initial maged stability regulations adopted in large heeling moment to a negligible 1MO Resolution A.265 (viii) as an alter- moment as the compartment filled up. native to SOLAS 1960 for passenger

ships. This requires a subdivision index A mean slope of 10°, for instance, oA (based on the ships lengths passenger!

the water surface ¡n the generator

crew numbers and lifeboat capacity) of room would cause a heeling moment 0.583, while the ship's achieved index of 12.4 MNm.

(based on simplified point probabilities Such aeymmetric flooding of symrne-of compartment damage and ship sur- trical compartments has not been pro-vivai) was only 0.437. Limited experien- posed before, to the author's knowled-ce with these subdivision indiknowled-ces indi- ge, but both NMI Ltd and the German cates that the EUROPEAN GATEWAY consultants

Schitlko (on

behalf of wassaferthanmostRo-Rovessels,due Townsend Thoresen) were Indepen-to its substantial subdivision below the dently driven to conclude that this ef-main vehicle deck; but was considera- fect must have been present, since the bly less safe than required under the _{other possible causes described above} probabilistic regulations, largely dueto _{seem inadequate to explain the} obser-its lack of freeboard to the main vehicle _{ved heeling. Subsequently, the Court}

Some lessons from the

accident

Irrprovementsto damage control

procedures

The sinking of the EUROPEAN GATE-WAY 1ol)owng the cothson occurred mainly because it was impossible to close the watertight doors sufficiently quickly. Until this accident, it was com-mon for UK ferries to operate with we-lertight doors in the machinery spaces Open, except in fog. The relevant sec-tion of the Merchant Shipping Regula-tions, 1980, states that every watertight

door "shall be kept closed at sea except when it is required to be opened for the working of the ship". The practice is therefore justified to some extent by the need for the small complement of engineers to have immediate access to all the machinery compartments in ca-se of breakdowns or fires. The Court considered that it was reasonable for the EUROPEAN GATEWAY to have open the two doors furthest att, but that lt was not necessary for the working of the ship to leave tho door between the generator room and the stabiliser room

open.

The NMIFLOOD simulations suggested that even with this door closed, the EU-ROPEAN GATEWAY would probably have sunk in the weather conditions at the time of the accident, ullthough she

might have survived in calm water.

(Data from Ref. 3 was used to evaluate the likelihood of capsizing due to wa-ves.) With all doors initially open, the

simulations demonstrated that only

power-operated doors, closed within 50 seconds of the collision, could have saved the ship. The Court accordingly recommended that all ferries be fined with power-operated doors (Indeed, this had largely become UK practice following the accident).

Improvements to the subdivision of Ro-Ro ships

Although the EUROPEAN GATEWAY satisfied the current UK requirements for passenger vessels, it proved to be vulnerable to this type of accident in the particular circumstances where the hull was breached below the waterline and also just above the bulkhead deck. This deck (the main vehicle deck)

beca-me imbeca-mersed at only 10° heel, allowing water to flood the entire length and width of the ship. The NMIFL000 si-mulations showed that once 12° heel had been reached, water entered this space at such a rate.that even with all, watertight doors closed the ship would eventually have capsized or grounded. Probabilistic methods of calculating damage survivability may well provide a more reliable basis than the current damaged stability and load line rules; both for assessing possible improve-ments and for regulating the subdivi-sion of these ships.

Implications of transient asymmetric flooding

Only the lack of a better explanation for the sinking of the EUROPEAN GATE-WAY points towards the existence of asymmetric flooding in symmetrical corn pa ri n ts.

Furthermore, ii is likely that such a phe-norrrenon would only occur in certain crowded compartments or with certain sizes of damage holes. Nevertheless, the concept has considerable impor-tance for the assessment of the dama-ged stability of ships. In particular, it suggests that rapid local flooding may be accompanied by rapid heeling, and that in such cases the statutory free-board requirements may be inadequa-te to prevent exinadequa-tensive further floo-ding. More research into this pheno-menon is underway at NMI Lid. Finally, a model reproduction of the sinking, in-cluding consideration of scale effects.

would confirm or modify the

NMI-FLOOD simulation, and could be

extert-dod io show the probability of this type of sinking recurring in the future.

Conclusions

The sinking of the Ro-Ro ferry, EURÒ. PEAN GATEWAY, following a collision, occured surprisingly rapidly. The tech-nical Investigation, although relying on somewhat uncertain evidence, was able to interpret the collision accepta-bly, but was driven io postulate a new phenomenon - transient asymmetric flooding - to account for the rapid heel-ing of the EUROPEAN GATEWAY. The sinking occured because the ship had its three watertight doors ih the machinery spaces open at the time of the collision, and could not close them

sufficiently quickly. A simulation of the flooding revealed that the doors would

have had to have been closed within 50 seconds of the Collision tO have saved the ship. Furthermore, the extensivo vehicle deck, exposed by the damage. nd the low freeboard of this type of ship, made the EUROPEAN GATEWAY certain to sink once it had reached 12° heel in its damaged condition.

The investigation demonstrated that power-operated watertight doors are essential for Ro-Ro ferries, but thai even with these, such ships are extre-mely vulnerable to rapid flooding. As the Report of the Formal Investiga-tion warns, "it cannot be satisfactory to proceed upon the basis that no passen-gar vessel will ever again suffer a fate

similar to that of the EUROPEAN

GATE-WAY". It is to be hoped that the lessons from the sinking of this ship will be hee-ded in time to prevent the catastrophic loss of life, which must surely occur, Ifa fully-loaded Ro-Ro ferry is ever the vic-tim of such a collision.

-5LOPE OF WATER5URFACE s ER.

5

flooding Simulation RcsultsFlowrate through

Holes (tonnes/sec)

flooding Simulation ResultsTransient Effects Time (sec) Bclow Waterline Above

Waterline Time(sec)

CG Offset (m) Moment (kNm) Slope (deg) 000 0-00 0-00 0-00 0-00 O-00 0-0-J o 10.00 2104 0.00 10-00 4-SI 8421-07 8-62 20-00 ¡9-76 0-00 20-00 3-90 14596-42 12-01° 30-00 15-65 0-22 30-00 3-33 16780-48 13-12 40-00 13-32 0-88 40-00 2-81 ¡5718-68 ¡3-60° 50-00 12-3 1 1-56 50-00 2-33 13686-77 12-91° 60-00 il -65 2-15 60-00 1-90 11428-45 12.280 70-00 II-45 2-81 70-00 I-SI 9 176-70 11420 80-00 II-41 3-69 80-00 I-17 7110-81 178 90-00 II-40 4-95 90-00 0-87 5282-10 10-82° 100-00 1131 6-43 100-00 0-61 37 16-79 11-92° ¡10-00 ¡0-81 9-01 ¡10-00 O-40 2407-00 14-76° 120-00 10-37 ¡2-82 120-00 O-23 1376- ¡9 19-30° ¡30-00 9.57 ¡7-92 ¡30-00 O-II 641-86 t3-02 ¡40-00 9-IO 23-62 140-00 O-03 192-67 5-13 ° o

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DEPT. OF TRANSPORT RECONSTRUCTID N o A

THE NAVAL ATCHI1ECT NAR86

TOWNSEND THORESEN RECONSTRUCTION o o o NM IF LOOD SIMULA1ION -MASTER'S STATEMENT TOWNSEND THORESEN RECONSTRUCTION KE TO SOURCES O SURVIVORS STATEMENTS

A TOWNSEND THORESEN RECONSTRUCTION O DEPT OF TRANSPORT RECONSTRUCTION

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II II

EUROPEAN GATEWAY

HEEL VR5U3 TIME

.J.R. sPOuGE

In reply to Mr Hannah, the estimated vertical centre of gravity (KG) in the casualty condition was based on an inclining

experiment which was carried out on this ship in November 1980. The centres of gravity of the trailers on board were assumed tobe

2 m above the relevant deck, as advised in the stability booldet. The KG estimate was therefore as good as is usual with such

estimates, but Mr Hannah's concern about its accuracy is certainly justified, since the implicit suggestion, a variation of which is made by Mr Heather, is that a higher KG and hence a lower metacentric height (GM) could have allowed the rapid heeling to be interpreted in a traditional way as a simple loss of static stability, without having recourse to transient asymmetric flooding.

The author would agree that the GM could have been slightly lower than eiiirnated, and consequently that tbeiiiagnitude of the transient asymmetric flooding could have been somewhat less1 but is convinced that this does not allow the transient effects to be dispensed with altogether.1t should be noted that, although the GM is commonly over-estimated, there is no actual evidence that it was so in this case.

Fig. 14 gives the simulation results requested by Dr Morrall for the maximum damage case defined in the current damaged stability regulations, which for this ship consists of damage 6'9 m wide, extending from the baseline upwards without limit and 4 m inboard from the ship's side. With the watertight doors closed, and using the same transient effects as in the simulation of the actual damage condition, the vessel heels over rapidly, but fails to immerse the main deck sufficiently, before the generator room fills and the ship rights itself with a final freeboard of O'93m. Water which reached the main deck during the transient

hTing causes a residual heel of 3 .40 With the watertijht doors

the ship heels over and capsizes within 40 sec of the collision. It must be noted, however, that the transient effects for this condition are even less certain than for the actual damage case.

OPEN WATE1TC1HT DOORS

TO EE CLOSED WITHIN 30-50

SEC!

30

o

20

10

o

O

DOORS TO B CI.O5D (J

403EC

J

Mr Heather's forthright comments on watertight doors are appreciated. Mr Meek and Mr Adams, Mr Brown, Mr Hobson, Mr Cleary and Lt Fiebrandi, and Professor Kundu all raise the same issue. Mr Brown makes an apt reference to the sinking of HMS VICTORiA, which was holed by the ram bow of another warship. lt was calculated that the vessel would have survived if all watertight doors and gun ports had been closed; and although an order to this effect was given one minute before the collision, it would have taken three minutes to carry out, and by then the flooding was out ofcontrol. lt is not difficult to conclude that watertight doors which are slow to close are extremely dangerous, and it is tragic that merchant ship designers had

forgotten this by the time the EUROPEAN GATEWAY was built. Mr Brown and Mr Heather further judge that watertight doors should not be fitted below the waterline at all. However, this deceptively simple conclusion ignores the good reasons why the doors were put there in the first place.

Doors between machinery spaces are used for many

watchkeeping and maintenance tasks, as well as t'or escape routes in some vessels, and their elimination would make these tasks much more difficult. This may be acceptable on well-manned warships, but the small increase in complement, which Mr Brown allows would be necessary, may be economically unrealistic on merchant ships. The use of remote machinery monitoring and tire detection systems (which the EUROPEAN GATEWAY did not have) make doors less vital, but any restriction in access to the source of ari accident such as a fire may allow it to get out of control. Watertight doors therefore, while decreasin the vessel's safety in the event of a colhsion, which is a remote risk but has extremely serious consequences, also increase lis safety in the event of machinery fires and other similar accidents, which are rather more hkel though less serious. The question of whether or not to fit watertight doors and, if fitted, whether to leave them open or closed, depends on balancing these two risks. The Inquiry

into the loss of the EUROPEAN GATEWAY decided that with the data at present available any conclusion could only be subjective. (Their interpretation o! the legal position is given in reply to Mr Cleary and Lt Fiebrandi). The author's subjective conclusion is that,power-operaicd watertight doors are necessary, and that they should be left open only where the frequency ol engineers passing through them is high and the risk of collision is low. Collision data certainly support their closure in fog, and may also give support, as Mr Heather recommends, for their closure when coming into and out of harbour.

NMirL 000 ---1IMULA'rION Q' Q.

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How to meet future standards EroEosed b>

1MO, Londen

1979?

TTDamage stability of passengerships.

Draft amendments to regulation 11-1/8 of SOLAS 197k

issued by the 1MO Subcomittee on stability 32e

session.

Required Stab.,Arm Curve in final damaged condition:

GZ min = 0,10, range min

= 15°, area min 0,015 m rad.

In intermediate stages: CZ min = 0,05 m range min =

7°

Maximum angle of heel

15° before equalization

7°

after flooding of

1

comp.

12° after flooding of more comp

In final damaged condition, he linq moment by

pass.)or

boats.or wind, H moment

(GZ-0,05) x displacement

should be met.

- CZ min =0,10 m,

is logical to our opinion.

- area min = 0,015 m, up to the crUfftalanÌe, ¡s

defining

hèmthinT6f

hihcoüTd bi bsorbed

by the damaged vessel and is

in line with the famous

stability-criteria of Rahola.

- range min = 15e, seems to b

of no sense, because of

the fact that the critical angle has been passed

al ready.

on a

ro ro vessel the critical angle is at imersion

of the cardeck(-8°)

PiS

P20

on a pass.vessel the critical angle is at innersion

of the corridor(14°) which is runninq along the

wing cabins, on top of the bulkheaddeck.

This

proposed area 0,015 mrad and 15° range are

difficult to implement on a current type of ro ro

passengervessel, which is characterized by a

low-level

bulkhead deck, with the ro ro space extending over the

full breadth above this deck.

- With two engine compartments being flooded, the free

surface reduction is

large and presents generally the

most critical damaged condition.

- Because of the low freeboard, the character of the

CZ-curve is

in stead of normally L-1

_{and to meet}

the requirement of GZ min = 0,10-range min = 15°, the

onliest way is to design a very beamy 'stiff' vessel.

Reason for this

¡s the small heeling angle (7°-8°) at

which the bulkhead deck is reaching the waterline and

where the CZ stability arm is at its maximum.

PZO

-Recent calculations are indicatingavalue of min.

intact CM required of about 5 m! which will result in

wildly rocking motions of the ship when sailing in

-

Increase of freeboard is offering no good solution,

because of the centre of gravity is raised

simultaneously. Moreover, the extra space gained below

the bulkhead deck cannot be used for ro ro cargo.

Meanwhile the danger of capsizing is still there if

the full breadth of the cardeck is covered by water

which might happen in case of firefighting.

- My conclusion is,

that the current ro ro aass desi2n

should be abandoned:

buoyant sidewalls around the ro ro saace should be

erected wh i cF wTTT a I low Tor the 0,015 mrad-çip

_{(RT ACL.}

requirement

in damaged condition.

-

_{In this design the definition of a margin line is}

complicated and, to my opinion, the requirement of

keeping this line above water has lost

its

significance.

PI

20

27 23

Fig.

13 -

In the case of a pure passengervessel, the 0,015 mrad

requirement in damaged condition could be met by using

'buoyancy' above the bulkhead deck which is created by

the presence of fire bulkheads and cabin partitions,

retarding progressive flooding.

P.Z

-

For the distant future, where large Catamaran type

passengervessel might appear, permanent buoyant wino

hulls are a necessity, because this type cannot

regene ra t e stab i I i ty.

rus

iEAN

s t _ACTICAL UOvANcy

IMPROVING EXISTING RO RO PASS SHIPS TO A POSSBILE HIGHER

STÑD

GF TM

To my opinion, existing ro ro pass vessels should not he

reduced in their carrying capacity.

- Transverse gui I latine bulkheads wi Il hamper the ro ro

pr i nc i p I e.

- Lonqitudinal separation bulkheads in the ro ro space

are unpractical.

- Permanent buoyancy in the wings of the ro ro space

will reduce earning capacity and does not reduce the

increased heelinq in the first minutes.

- Sponsons are preferable and extra displacement - aft

will solve the general problem of 'STERN-TRIM', a

shortcoming of many ro ro vessels.

PIO-H-25-26

However, the ro ro terminals should be adapted to the

Improving the safety of ro-ro ships : BUOYANCY IN ThE WINGS

A study

by J. G.

L. Aston and L.

J. Rydifl

(University College London)

Tl-i. ßPVAL ARCHITECT APR87

TRAN5VR5E 5UeDVI5ION

+ SLE WALLS FLAR

L

/

BA5E+ IMCRLA5O BE'M

The improvements to stability shown in the two cases above come pai-tly from the in-crease in waterljne beam of the flared hulls

but mainly from the resen'c of buoyancy

provided in the added side compartments. Further Lests havc shown the sensitivity of the stability improvements to the

distribu-uon of this buoyancy reserve. Cases have

been euninc4 in which the flared sìdc

com-partments were taken from the existing

water line, thereby preserving the original

GM value. The results show thai

submergence of the vehicle deck takes place

beforc sufficient buoyancy from the side

compamnents can come into effect, so that although equilibrium and positive stability can be achieved, the equilibrium angle is ex-cessive I N TA C.T DA MA G .

UyANy

: TOO LATE.

_OT EFCJ..ÑT

t

M ÇZ. NEL ltSQL 1L. Equilibrium modification dama9e (b). MiLL AMA4E s.

\

EASE"

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LONGITUDINtL SUDIVI5 ION

+ LWAL.L

I

FLAREp

+ .IDEWALL

II ELARC

condition for hull with extreme

+.S IDWALLS

O°1EL

The second modification shows

the obvious advanLige of incorporating

reserve of buoyancy high up on the vessels sides. I...,, ( ..S _- ço_

. 1...

_{L. UO}

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Rec.uE

SiTUATION TODAY

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FUTURE FOR EXI3TING VE5SELS

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MERCHANT VESSEL CONVERSiONS: THE FALKLANDS CAMPAIGN

20

R. NANNAH

Ti

NAVAL ARCH!T.CT Fal ¿4

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MARGLN LINE NOT TO BE SUBMERGED

5TArtDAR0 Ij5û DTL

3NSI

DAMAGED

Fig. 6.

Simple Comparison of Frigate and Passenger Vessel

Minimum GZ Curves: Intact and Damaged

THE

RoRo vesscl poses an additional hazard in that the

submergence of the vehicle deck would cause such a massive

loss of stability that catastrophic capsize could occur.

The alterations carried out on the passenger ships were not

necessarily approved by the DTp, although the MOD's policy

was to endeavour to meet at least DTp rules where this was

possible. The help and assistance of the DTp in these matters

was of crucial importance in reaching the inevitable

°ompromises which were necessary under the emergency

circumstances. However, of the five vessels primarily engaged

to carry large numbers of troops, only one sailed from the UK

within her passenger vessel load line limit.

The conclusion that can he drawn on stability matters is that

the use, in an emergency, of merchant vessels in support of

military operations, especially for the carriage of troops or

vital equipment,

is potentially very hazardous.

cz

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23-;s AR

INTERPiEDIAft SIACES

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AREA>, 0.015 MIRAD.

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"RANIEREqlUIREMENT

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Et? U II.ib. CRITICAL dIR. V. HOORdP4 - Y.fl CII N ,oOs LUY

STABILITY 0F PASS.VE5SEL IN DAMAGIED CONDITION

EXAfr1PLE

0

IN CASE OF THIS VESSEL

Lt ßRtUrt

O.7J

IP4TERPRETTION O

(MO SLF 32 WF6

LONDON SEPT '87 OE40 020

MINIMUM Z,,OiOM

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WANTED B

THE DESIÇNER:

iTEt? R5EARCÑ RcARDINC Tl-I

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TO THE IRSS OF WATER sr

i-

_{DAMAGED VISSEL}

TRAN SIN1 AMMtETRIC

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ELJLKHDS /CA(N PARTITIONS

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PERfI PROVISION .

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DEVELO PlIENT OF PER MANENT 8UO'yNCy N ORDER TO REDUCE PERr1EASILITY.

Ttiis ßVc'ANCy To SE. PRACTiCAL IN MANy ASPECTS

COST RESISTANCE To COr1PRE5IoN

WEIGHT CORROSION

INSTALLATION (LASHIN)

FIRE I-IA2ARD

RErrnVA L.

StEARC-i REcARDIN

Ar1AE .STASILIT7

EU!REr1ENTS

¡N WIND AND SEA

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ON AOOVE MENTIONED SuEcrs t-A.5 LEAD TO CONCLUSIONS

AND.

ALL EXPIERENCES,-qAINEO SO FAR

HAVE. SEEN TAcEN

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THE. DESIC1NER

LII<ES

TO E CONF(ONTED

_{ITt1 INTERNATIONALLy}

AGREED REwREnEÑT

fl

?I?ELU1INAR'1 FOPOS IT(ONS REGARDING

_{DAMAc-STABILITy. REÇUIRErIENTS}

5rA3ILI1

ARM 2. TO C3E

AT LEAST OtO M

UP TO TI-lE- CRITIC.AL ANGL.E

THIS 50 CALLEO DYNAMICAL LEvER' AT THE CRITICAL ANALE.

IM LINE WITH RAHOLAS PRINCIPLE.

CRITICAL AMLE

_{WHERE PRORE,SIVE FLOODING STARTS}

WHERE CARAO STARTS 1IOVIN

WNEE. PANIC STARTS AI1ON

PAs5ENER$ :7-IO

WHERE LIFE SAVINÇ APPLiANCES ARE FAILING.

A RApÇE. 8EYOND THE CR11. ANGLE io 8E U5.D AS INDICATION

_ONLY

RESEARCS-1

¡5 WANTED REGARDING HEELING ANGLe,IN CASE OF RUDDE1 hARD-OvER

ON A FAST - HIGH S IDEO. SHORTTURNIN

_{VESSEL AT FULL 5PEED}

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100

FERRY

CARDECK OVER FULL SEAM

IN DAFiAGW COND.

: 0,015 MRAD AREA UP TO C.RrrICAL ANGLE

(RAiOLA) AS PRELiMINARY PROPO5ITION fOR DYNArIICAL LEYER'(LIIrÏ) BEINC AVAILAbLE

FURTHER RESEARCi- flIGHT If4COCATC,WEThEV IT i TOC LA E,O TOO Sr'iALL.

ojo

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P 24 26

23

IN CASE HARD RE(UIREMLNT5 WILL BECOME MANDATORY,

WHAi

TO DO

?

to ro ro passenger ferries not complying with

_I8OSÎANDARr

SCRAP PI N C A LT E R N A T V E.

For instance 'EuroEean Gateway' t>Ee: to have

sponsons

filled with drums

'Modern ferry' complying with 1980 standard and

consequently not suffering from irrrnersion of the

bulkhead deck, might be improved by filling the void

wings with polythene drums and engine

room wings with

steel drums.

Adding sponsons only in case of absolute necessity,

which could be concluded aftér research

_{on transient}

asymmetric flooding.

Norsun/Norsea tEe ferry: filling void wings with

polythene drums or alternative buoyancy if

necessary.

'New Desi9n' :

_{continuous longitudinal bulkheads and wide}

wal is around ro ro space.

All void compartments to be fi lied with polythene drums.

? 25 26

P 27 28

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NO 5LEEP1N

ACCOMMODATION BELOW ThE BULKHEAD DECK

FIN5 SHOULD FOLD-IN

IN AFTDIRECTION

e

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FOLI AFT.

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NOT RISKY ANA MLiA NOLAND

iscy: 4Z

14TURIyt7/

30

I 3.5(

3.6

Hull inteqrity, some critical technical aspects

- All doors in access oeninqs to the car deck to be

Tittea wTtF indicator TigEts.

- closed television circuit on cardecks at door control

stat ions

- water on cardeck to be drained quickly via large ducts

or pipes towards tanks or bilges in the lower parts of

the vessel (free surface effect of these slack tanks

to be kept small)

. P 12. TOP

Scuppers with non return valves to overboard should be

avoided because of possibility of clogging

(maintenance is difficult).

- stabilizer fins to 'fold in'

in aft direction.

P30

Surrounding structure shourd be such, that main

compartments to be secured even after the fin has been

hit by an obstacle.

- WT-doors closing system self contained and remotely

control led.

RaEid

disembarkation in case of emerency

- no sleeEino accorrrnodat ion below the bulkhead deck

(- freeboard deckT on new ro ro pass. ferries!

Pli 13.2ui

- wide escae routes - dimensions according to

_P30

international agreement by 1MO.

- self contained emergency

I ightin

- wide musterstations preferably on low-deck-level

connected to 'MES'

- suitable means of escae throuh ships side

- Disembarkation by means of low level marine escape

slides ('MES') and rafts.

_P1lZ425

- quick releasedieseldriven man overboard boats (type

rigid inflatable) to serve the flotilla of rafts.

Y FA57 AvT

cr.cs)

- Stab i

li ty check

- reliable draTt recordín

_auaes

- weihin

oT

freiht vehicles

3V valHlNC.ID

r TERrINAL

-

electronic loadmaster suitable for use on ro ro

vessels

-exElicit stability instructions (including influence

of trim by head and by sternY presented in accessible

form.

- alle existing ferres to be subjected to Eeriodic

stability check in 4 years intervals: lightweight

cFeck and inclining test (if necessary)

- Car90 related Eroblems

-

lasing of vehicles

- seaworthy stowage of cargo in containers

- dangerous cargo

- responsibility

Procedures

- mandatory formal systems aaaroach

- checklist before departure/arrival

- uniformity in terminoloy

RO-RO PASSENGER FERRIES

INCREASE OF 5UPESTRUCTURE io . 9a7

g-vR :CAS1

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Steerin

and manoeuvring:

Ability to manoeuvre into port entrance and alongside

berth in strong wind (uProBF 7)

sea swell and current.

"l-flCH -LIFT FLAP

LJDDE.RS POWERFUL OWTHRU5TERS

P33

- Course keeping ability when slowing down with C.P.

props at zero pitch in which case rudders are

blanketed.

- Good 'crabbing performance' by rudders, propel 1ers and

thrusters, to allow for moving in transverse direction

only.

- Ability to turn on the spot.

- Course keeping at sea; possibility of broaching in

oblique followinq seas.

- Considering the danger of large heeling angles in case

of a sudden 'hard-over' ruddermanoeuvre at

ful I

power.

This is a special problem on fast,

'short-length',

'built-up' vesseishavinga small turningcircleat

full speed.

"Herald of Free Enterprise" would have heeled by

centrifugal moment at 19,5 knots,

in a

turn of 214 rr

diam. (1,7L) with intact GM = 1,6 m to a static angle

of about 25°.

Takinci into account the dynamic behaviour, the max. heel

would have been larger.

P 35

SEecial case: "Herald of Free EnterErise", leaving

Zeebrue, March 6th, 1987

- During 'speeding up', the cardeck got burdened by a

free moving mass of water, which entered via the bow

door opening.

- Her stability went down rapidly and the tender vessel

became very sensitive to small rudder manoeuves and

flow disturbances (squat).

OUTSIDE OFTPIER A SWING TO.5E3 StARTED

-

Beyond a certain angle of heel, the flared

belting-forward touched the sea and after imersing started to

excite a

large side force in combination with the

forward skeg.

- The yawing moment of this side force overruled by far

the steering moment of the vessels rudder toFort1when

trying to steady the ship

ir

HER SWING

-io 58.

- The 'counter rudder' might even have increased the

centrifugal capsizing moment

-I936'Ran'

Il disaster,

whale catcher,capsized in turn).

- Additional to this effect came the capsizing moment by

the sternwave, overrunning the vessel.

- The heeling moment of the mass of water on the cardeck

moving to the

' lee side' must have been the main

reason for a rapid capsize.

I.

CEMTRIFL)AL

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