maib’s interpretation of the results of the model experiments · pdf filemaib’s...
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175
Annex 4
ANNEX 5
MAIB’s interpretation ofthe results of themodel experiments
The model experiments made an invaluable contribution to the investigation, revealing thevulnerability of even a well-found vessel such as Gaul to an encounter with a group of verylarge breaking waves.
Model experiments provide a satisfactory way to predict performance and behaviour of thefull-scale vessel, although there are often inherent limitations. This is because themodelling is of necessity a simplification of the vessel and the environment, and the resultsmust therefore, take this into account. Model experiments in steep breaking waves are theonly viable way of predicting the ship’s response to extreme seas.
The model used possessed greater stability (scaled) than the full-size vessel, simply becauseof unavoidable effects of scale. For example, the 1 millimetre thick bulwarks on the modelscale to 46 millimetre full size, about six times the real thickness. The range of stability ofthe model was determined by experiment to be almost 180°, which meant that it wascompletely self-righting. This was not realistic as the full size vessel was calculated to have arange of stability of about 120° (Figure 10 in Annex 2). However, the calculations for thefull size vessel ignored many minor items of buoyancy such as the winches and box sectionmasts. If these items had been included, the calculated range of stability of the vessel wouldhave increased, but not to 180°. The range of stability of the vessel probably lay between120° and 130°. This would of course be rapidly degraded by flooding through non-closeableopenings.
As a consequence of its exaggerated range of stability, the model would not have beenknocked-down to as large an angle as the full size vessel, and would have recovered morequickly. In effect, a knock-down on the full size vessel would have been worse than impliedby the model experiments. For this comparison it has been assumed that both the modeland full size vessel are completely sealed against water ingress, which was also unrealistic.However, the experiments carried out with doors and hatches opened, showed that waterwould not have flooded in fast enough during a knock-down to have prevented a partialrecovery of the vessel.
Also, the model was not fitted with the minor ventilators on the starboard side, which ithas been estimated would have increased the rate of flooding to the factory and otherspaces during a knock-down. Again, this factor would have allowed the model to recoverbetter than the full size vessel.
176
Marine Accident Report 4/99 ‘Gaul H 243’
The effect of cargo and gear shifting was also not represented on the model, nor theblockage of freeing ports from loose gear sliding across the trawl deck. Both these effectswould have been critical to the survival of the vessel.
The model experiments are indicative of what could have occurred with the vessel, butprobably exaggerated its ability to have withstood, and to have recovered from, a knock-down. Therefore, the data gleaned from the model experiments, when scaled for the full-size vessel, could be optimistic. However, the calculated large range of stability of the vesselstrongly indicates that she would have made a partial recovery from the knock-down.
Nevertheless, in spite of inherent limitations of the experiments, it is concluded that if thevessel had been struck by a large breaking wave it would have been rolled to an extremeangle and this would have compromised its safety.
179
Life raft containers
Stairs down
Wooden door Man overboardlifebuoy stowageP & S
Wooden door
Life raft containers
Figure 1: Gaul – bridge deck layout
Radio room
Chartroom
Ship’swheel
Flaglocker
Controlconsole
Haul/shootconsole
Han
dra
ilWooden door
180
Figure 2: Kurd – bridge interior looking to starboard
1
2
3
45
6
11
10
12
7
8
9 KEY:
1 Ship’s wheel
2 Rudder angle indicator
3 Voice pipe
4 Periscope for binnacle compass
5 Searchlight handle
6 Voice pipes
7 Radar set
8 Gyro compass repeater
9 Steering tiller for docking
10 Stairwell
11 Chart room
12 Control console
181
4
Figure 3: Kurd – bridge interior (looking to port over control console)
2
3
6 5
1
KEY:
1 Haul/shoot console
2 Fire alarm panel
3 VHF telephone handset
4 Autopilot controls
5 Chart room
6 Radio room
182
KEY:
1 Autopilot control
2 Paper plotter
3 Radar
4 Gyro compass repeater
5 Elac echo sounder
6 Echo sounder
7 Propeller pitch control lever
Figure 4: Kurd – bridge interior (control console, looking forward)
7
2
1
3
4
56
KEY:
V = Natural vents to factory
1S, 1P…13P = Location of freeing ports
LKR = Locker
183
Figure 5: Plan of trawl deck (aft)
Looking forwardalong trawl deck
FISHLOADINGHATCH
FISHLOADINGHATCH
STERNRAMPGATES
HATCHTO NETSTORE
GOALPOSTMAST
“A” FRAMEMAST
SPARE BOARDSTOWAGE
STARBOARD
VENTS TOENGINE ROOM
DOOR TO FACTORY
DOOR TO ENGINE ROOMESCAPE
HATCH TOFISH MEAL
HOLD
DOOR TOACCOMMODATION
V
HATCH TOFISH MEAL
HOLD
22" DEEP BOBBIN RAIL P&S
ENGINE ROOM VENT
SPARE BOARDSTOWAGE
PORT
HATCH TOENGINEERS’
STORE
Typical freeing port
V LKR OVER
LKR OVER
TRAWLWINCH
Looking to Port
V
V
Plan and photographs courtesy of BAe Land Sea System
184
Figure 6: Kurd – looking aft along trawl deck
KEY:
1 “A” Frame mast
2 Goalpost mast
3 Net store hatch
4 Fish loading hatches
5 Stern ramp gates1
2
34
5
4
185
Figure 7: Kurd – looking forward along trawl deck
KEY:
1 DF Aerial
2 Main mast
3 Liferafts
4 Door to accommodation
5 Net arena
6 Bobbin rail
7 Door to factory
1
2
33
4
5
6
7
186
Figure 8: Kurd – stern ramp and gates
1
2
KEY:
1 “A” Frame mast
2 Goalpost mast
3 Port trawl door in its stowedposition
4 Hydraulically-operated sternramp gates closed
5 Starboard trawl door in itsstowed position
34
5
Figure 10: Arab – trawl deck, starboard. Door to factory
188
1
34
5
2
KEY:
1 Natural ventilation inlet to factory
2 Door to factory
3 Loop used for holdingdoor open
4 Emergency escape doorfrom E.R. (Fig. 9)
5 Stowage rack for sparetrawl doors
189
Figure 11: Arab – trawl deck (aft), looking aft. Fish loading hatches, open
Photograph courtesy of BAe Land and Sea Systems
KEY:
1 Hatch to netstore, open
2 Locking pin
3 Securing clip
4 Goalpost mast
1
2
3
3
3 3
3
4
3
2
191
Figure 13: Description and technical specification of Sealion ROV
Reproduced by courtesy of Racal
193
Figure 14: Sidescan sonar image of wreck
Note: 1) Areas shaded in purple are fishing nets caught in the wreck.
197
Figure 18: Photo mosaic of starboard side
The photographic mosaic is incomplete in those areas where there was not sufficient detail or the correct perspective provided by the video survey.
198
Figure 19: Photo mosaic of port side
The photographic mosaic is incomplete in those areas where there was not sufficient detail or the correct perspective provided by the video survey.
202
Figure 23: A typical steerable Kort nozzle
Figure 24: Gaul’s Kort nozzle viewed from astern
Photograph courtesy of Kort Propulsion
Figure 26: Photo mosaic of deckhouse front
204
Weathertight door toaccommodation
closed and secured
Bridge deck
(P)(S)
Forecastledeck
206
Figure 28: Control console (front, looking to port)
Figure 29: Control console (starboard forward corner)
Autopilot mssing
Radar
Elac echosounder
Echosounder
Rottingpanellingaroundconsole
Note: See Figure 4 for photograph of control console
207
Figure 30: Steering position at bridge front
Tiller to port
Gyrocompassrepeater
Autopilot/Tillerchangeoverswitch
208
Figure 31: Radar set below bridge windows
Note: (1) Hood is missing(2) Cathode Ray Tube has imploded(3) See Figure 2 for position and, appearance of original radar
Hatch cover Access opening
Figure 32: Open access hatch on aft face of port funnel
209
Figure 33: Looking aft onto the open fish loading hatches
Note: 1) The dark border to the hatch covers is the rubber seal which ensures that they are weathertight when closed.2) The hatches are undamaged.
Looking down onto open fish loading hatches
Starboardhatch cover
Porthatchcover
210
Figure 34: View down outboard edge of port fish loading hatch
Note: 1) Locking pin should have been visible in this view, it is missing.2) Securing clip is in closed position, but is undamaged.
Portbobbin rail
Port fish loading hatch
Securingclip
211
Figure 35: View onto port bobbin rail showing port stern ramp gate fully open and in its recess
Aft
Port bobbinrail
Port sternramp gate
Port fishloading hatch
Forward
212
‘C’ Class boat davit, stowed
Liferaft rack, empty
Forward
Nets rising from net arenaAft door to net store, open
Spare trawl door stowage rack, empty
Aft
Figure 36: Photo mosaic of port side trawl deck
Liferaft rack empty
Inflatable boat missing
Forward
Door to factory, open
Nets fallen out of arena tostarboard
Aft
Spare trawl door rack, empty
213
Figure 37: Photo mosaic of starboard side trawl deck
214
Figure 38: Bobbins lying inside net arena
Starboard side forecastledeck (aft)
Starboard coamingof net arena
Bobbin (1)
Forward Aft
Aft
Forward
Port coaming of net arena Bobbin (1)Bobbin (2)
Danlenobobbin
Note: 1) Bobbins (1) and (2) are connected.2) The danleno bobbin is a spare attached to the port bobbin rail.
215
Figure 39: Photo mosaic of ‘A’ frame mast
The net appears to be hungover a wire / rope which isthrough this block
Port side ‘A’ Frame stay, broken at lower end. Currently through ‘A’ frame, net tangled /wrapped around broken end.
Rope/Cable through top block on ‘A’ Frame ends here, broken end.
216
Figure 40: Partition bulkhead burst forward
Note: 1) This bulkhead was the forward bulkhead of the No. 2 four crew man cabin.
Upper partof bulkhead
Lower partof bulkhead
217
Figure 41: Desk drawers in mate’s cabin
Note: 1) Desk is facing to port, drawers have fallen out to starboard.
218
Line ofthinner wire
Line
of
thic
k ca
ble
240˚
295˚
Figure 42: Seabed cables in vicinity of wreck
Photograph of wires crossingApproximate position
of Gaul (length 66m)
245
219
Figure 43: Bow damage – view from ahead
Line of stem
Anchorbox
Fishingnet drapedover bow
Platingdished-in
Anchorbox
Platingdished-in
220
Figure 44: Section through net arena looking forward
BOBBINS
UPRIGHT
HEELED < 90º
HEELED > 90º
COAMING TO NET ARENA
BOBBINS
TRAWL DK
NETNET
TRAW
L DK
BOBBINS UNMOVED
TRAWL DK
TRAWL DK
NET
221
Figure 45: Gaul – Factors tree for the open fish loading hatches
Fish loading hatchesopen and unsecured
Opened as GAUL sankto the seabed
Opened without the crew’sinvolvement before the
GAUL sank
Opened by the crew
Pressure of trapped air in thefactory lifted hatches
The hatches fell openStoring a damaged
net in fish chuteEmptying a cod-end
in fish chute
GAUL rolledbeyond 90°
GAUL trimmedpast the vertical
Hatches began to fallopen when GAUL rolledpast 90° in knockdown
Hatches “jumped” opendue to GAUL ’s pitching
motion in wavesHatches fell open as shesank steeply by the stern
or or or
or oror or
or or
No No NoYes
No No No
COMMENT
(1) Calculationsshowed that there wouldbe insufficient pressure.
(2) If GAUL sank bythe stern and factoryflooded completely, therewould be no trapped air.
COMMENT
(1) Research hasshown that sinkingvessels return closer tothe upright and do notroll over.
COMMENT
(1) Positions of floormats in bridge indicatethis did not occur.
COMMENT
(1) Consistent withevidence and results ofmodel experiments.
COMMENT
(1) There is noevidence that this had everoccurred on GAUL
(2) It could only occurwith GAUL dodging head tosea in which case it wouldnot have led to dangerousflooding.
COMMENT
The fish chute wasfound to be empty.
COMMENT
(1) All theevidenceindicates thatGAUL was notfishing.
222
Figure 46: Gaul – accident factors tree
GAUL listing 35° tostarboard landed on
the seabed
GAUL lies on the seabedlisted 35° to starboard in
280m of water
Sides of fore peak waterballast tank crushed by
water pressure
Fish loading hatchesopened fully
Sides of forward oil fueldeep tank crushed by
water pressure
After GAUL left the surfaceshe levelled off and took up
a list to starboard
Partition bulkheadsburst forward
Water flooded throughsuperstructure from aft
to forward
GAUL sank steeplyby the stern
Water flooded her interiorthrough open doors and
hatches on the trawl deck
Doors and hatches immersed
GAUL listed at least40° to starboard
Cargo and loosegear shifted to
starboard
Trawl deckswamped with
water
GAUL heavilytrimmed by
stern
Factory flooded
Forward fueltank empty
Fuel usedfrom forward
tank first
Factory door open
Fish loading hatchesfell fully open
Tanks had not filledwhen GAUL reached
crushing depth
Tanks were filling throughtheir air pipes as GAUL
sank rapidly
Forward tanks emptybefore GAUL sank
Air pipes kept abovewater until GAUL sank
below surface
Fuel used fromforward tank first
Forward water ballasttank empty to give
stern trim for towing
Fish loading hatchespartially open
Hatches started tofall open
Non-return valve inhydraulics prevented
hatches closingEngine roomescape open
After GAUL had made apartial recovery from the
knock down, someone triedto escape from the engine
room
GAUL Rolledbeyond 90°
Hatches not securedagainst opening
Machinery stopped,engine room flooded
through ventilator
GAUL was“knocked down”
Impact dented the outboardface of the port funnel
KEY
As seen on GAUL’s wreck
Taken from evidence to the FI in 1974
Observed in MAIB’s model experiments
Taken from the vessel’s constructiondrawings
HOW TO USE THE “TREE”
(1) The tree represents the linkagebetween the many factors which theMAIB believes contributed to GAULsinking.
(2) For any particular factor, thosefeeding into it (i.e. those physicallylower in the tree) should give theimmediate reasons for its status.
(3) For example: the fish loadinghatches were found on the wreck to befully open, why was this? It wasbecause they had fallen fully open.Why had they fallen fully open? Therewere two necessary conditions for thatto have occurred: First, they werealready partially open and second,GAUL sank steeply by the stern. Whywere the fish hatches partially open?Again for two reasons:..........
..........and so on.
Hit by a group of verylarge breaking waves
GAUL beam on to sea
Some combination ofwind and waves push
bow around to starboard
Wind and waves 4 to 5points on starboard bow
GAUL making 170°in the direction of
Honningsvaag
Winds from ESEforce 8 - 10
GAUL heading forMalangan Bank whereother trawlers are still
fishing
GAUL heading forHonningsvaag forrepair or supplies
Rudder at 10° to 15°to port
or or
GAUL heading towardsHonningsvaag to gain
shelter of land
or
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