GB2206544A - Improvements to the damaged and flooded stability of vessels with fully enclosed superstructures - Google Patents

Abstract

In a sea-going vessel of the Ro-Ro type, the vehicle deck 11 is provided with bulkheads at intervals to prevent movement of water fore and aft which bulkheads are in place when the vessel is in transit but can be retracted or opened when the vessel is docked to allow the passage of vehicles on and off. In one arrangement, there are vertically-moving bulkheads 17 that extend for part of the height of the vehicle deck space and can be retracted downward in the slots 12 associated with fixed bulkheads 13,14 of the ship's structure under the vehicle deck. In another arrangement the vehicle deck bulkheads are fixed and have openings for the passage of vehicles which can be closed by means of roller-type shutters. In both cases, seals are provided at the sides of the moving bulkheads or the shutters and in the latter arrangement those can be inflatable seals. <IMAGE>

Description

IMPROVEMENTS TO THE DAMAGED AND FLOODED STABILITY OF VESSELS WITH FULLY ENCLOSED SUPERSTRUCTURES This invention relates to sea-going and like water-borne vessels with fully enclosed superstructures, especially vessels of the Ro-Ro type.

A considerable amount of cargo, mixed cargo and passenger tonnage comprises so called Ro-Ro vessels, that is vessels with a Roll on - Roll off facility for vehicles on to the bulkhead deck and, in some cases, on to a futher deck or decks above the bulkhead deck. Such vessels may have both bow and stern entry, in other words, a so-called drive-through facility, and this may be at the bulkhead deck level only or, in certain cases, may also be at a further vehicle deck superimposed upon the vehicle deck constituted by the bulkhead deck.

These vessels are generally of the fully enclosed superstructure type, with doors at the bow and the stern that are required to be fully water-tight, while a secondary door has to be provided inboard of the bow doors. The inboard door is, by regulation, an extension of the collision bulkhead and in the closed position must be water-tight. The vessel may be of one, two or more compartments standard. If purely for freight, it is generally of one compartment standard, but to hold a Passenger Certificate the vessel is usually of two compartment standard, or more.

The full requirements for damage stability and flooding apply; the conventional requirement for the bulkhead deck, ie. in this case the vehicle deck, is that it shall be situated 76mm above the marginline.

If, in case of damage, the side of the enclosed superstructure, or for some reason one or other of its ends, is breached, then it should not normally be possible for water to get on to the bulkhead deck (which, of course, is the lower vehicle deck in Ro-Ro vessels). This, however, is in the context of classic damage stability and flooding calculations, which assume calm water, and the transversely symmetrical flooding of transversely symmetrical spaces, ie. those without any longitudinal barriers, bulkheads or other divisions.

There are circumstances where water might enter on to the bulkhead deck through a transverse breach of the ship's side, or through a bow or stern door which has been damaged or is open, by virtue of either rough seas or the vessel's motion, or in the event of transient transverse asymmetrical flooding of a nominally symmetrical space.

In the first case, clearly with a bulkhead deck only 76mm above the margin line and a breach in the side, substantial quantities of water may well enter on to the bulkhead deck. In the second case, if the bow and/or stern doors are breached or are open, either seas or the vessels motion might cause substantial quantities of water to enter on to the bulkhead deck, ie. into the vehicle deck area. Or with asymmetrical flooding, although water will rapidly flood across a transversely symmetrical space if the vessel remains upright, should the initial entry of water be sufficiently rapid a considerable heeling moment may be applied at least transiently, causing a heel which may be enough to immerse the side edge of the bulkhead deck and allow a significant quantity of water to enter on that side, producing an irreversible heel.

It is a feature of such vessels that the enclosed superstructure is open from bow to stern, except for such casings as are required for passenger and crew access vertically and for the necessary ventilation, etc. for the nachinery spaces. This being so, once water starts entering on top of the bulkhead deck, ie.

into the vehicle deck area, it is free to travel the whole length of the ship, a very large free surface is present and the stability of the vessel is affected.

Assuming flooding of the vehicle deck to a small depth, if the vessel acquires any significant heel the water no longer is a free surface but becomes an asymmetrically disposed weight at the side to which the heel is directed.

The scuppers may well be incapable of clearing quickly or at all a considerable amount of water that has entered on to the bulkhead deck and the vessel may lose stability and acquire either a large angle of loll or capsize totally.

It is thus desirable in such vessels from the stability point of view to limit the movement of water either forward or aft from a side breach originating from collision damage, or forward or aft from a breached or open stern or bow door. This restriction of movement fore and aft, and hence confinement of any water to a small percentage of the longitudinal length of the vehicle deck, is best effected by transverse bulkheads of at least part height. However, any transverse bulkheads across the vehicle deck must obviously offer grave obstructions to the basic function of such a vessel and make it impossible to effect the ready fore and aft movement of vehicles, which is inherent in the design. Permanent transverse bulkheads forming perhaps upward extensions of the main sub-division bulkheads from below the bulkhead deck would clearly thus be very inhibiting economically.

An object of the invention is to provide means whereby such longitudinal sub-division can be effected, at any rate to part height, without substantially interfering with the basic longitudinal movement of the vehicles which is the primary aspect of the design of such a ship.

According to one aspect of the invention, vertically-moving bulkheads are provided which can be lowered into a stowed position so that their upper edges are flush with the deck, thus forming a flat surface over which vehicles can move. These bulkheads, which may typically extend some 2m above the level of the vehicle deck, may be housed in recesses on one side or the other, as may be most convenient, of each fixed transverse bulkhead below the bulkhead deck. It is not essential that they be fitted in way of fixed bulkheads but in a preferred form of the invention they are, this giving an economical and structurally desirable arrangement.

The vertically movable bulkheads may extend from casing to casing in the vehicle deck and will therefore be wide in relation to their depth. Suitable means will be described for ensuring that free movement of these bulkheads may be obtained without any possibility of them jamming by virtue of their high width/height ratio. They may be raised either by hoisting from the deck head above or by pushing, using screw, hydraulic or pneumatic jacks, from below.

According to another aspect of the invention, the bulkheads above the bulkhead deck are fixed and have openings to allow fore and aft vehicle movements, with movable shutters for closing the openings.

In the preferred form of this arrangement, roller shutters are fitted to the bulkheads, these roller shutters being housed in vertical channels in the bulkheads. There may be a single wide shutter extending across most of the breadth of the vessel, or two, three or more individual shutters establishing lanes. When the shutters are open, the vessel returns to the drive-through condition, but when they are shut the bulkheads, being then substantially water-tight, can carry the sub-division of the vessel effectively a deck higher than the bulkhead deck. By such means, the vessel is brought to the traditional design of a passenger ship in which fore and aft spread of free water above the bulkhead deck is prevented by internal divisions in the superstructure. This is not the case with the usual Ro-Ro vehicle ferry where any water on the bulkhead deck is free to flow fore and aft and in the process possibly destroy the stability of the vessel.

The steel roller shutter or shutters may slide in vertical channels in the fixed portions of the bulkhead, these fixed portions being in effect deep web frames extending from the ship's side inboard. Where there is more than one shutter door, there may be one or more further fixed bulkhead portions, either at the centre line in the case of two doors, or at suitable intervals off the centre line in the case of three doors or more.

The vertical channels can be arranged with a subsidiary groove in one side, either fore or aft of the door, this groove housing inflatable seals which, when activated, seal the edge of the door firmly to prevent water passing round the edges of the shutter from one side to the other.

Arrangements according to the invention will now be described by way of example and with reference to the accompanying drawings, Referring to Figure 1, through and beneath the bulkhead deck 11 a succession of vertical transverse slots 12 is provided, each preferably on one side of a fixed bulkhead 13. If a bulkhead with an upwards extension of say 2m is required the slot will extend below the bulkhead deck typically 3-4m. A suitable arrangement may be to use one side of the fixed bulkhead 13 as one side of the slot 12 and to dispose a partial fixed bulkhead 14 forward or aft of the main bulkhead to form the other side of the slot, there being a shelf 15 of the partial bulkhead 14 extending to the main bulkhead 13 to form the base of the slot 12.Suitable adjustment pads 16 may be fitted at the bottom of the slot 12 to ensure that in the stowed position the top of a movable bulkhead 17 that slides vertically in the slot is level with the vehicle deck 11.

If extensible rams 18 or screw jacks are to be provided beneath the movable bulkhead 17 for raising it, there may be tubular or rectangular wells 19 of suitable length formed in the bottom of the slot 12 at each end in order to accommodate the rams or screw jacks.

The movable bulkhead 17 may be of any suitable form of construction, but is preferably of box construction, not necessarily water-tight, although a single-plated construction with stiffeners may instead be used, the bulkhead being arranged in both cases to slide smoothly in the slot. At the upper edge of the bulkhead a flat top is provided, either the top of the box if of box construction, or a flat plate at the top of the stiffening grill structure of the single-plate type of bulkhead. This flat plate at the top of the movable bulkhead, when flush with the vehicle deck, will form a suitable surface on which vehicles may move.

In order to prevent the ingress of dirt etc. into the slot, a heavy rubber sheet 20 can be provided at the top of the movable bulkhead (Fig 2), this extending over the slot 12 and overlapping on to the vehicle deck 11 when the moving bulkhead is stowed to afford both a flat surface for vehicles to move on and also a seal against ingress to the slot itself.

In the case of a movable bulkhead 17 lifted from the deckhead above, suitable means for doing this, such as power hoists 21, may be arranged at the ends of the bulkhead to raise it as required.

When raised, the movable bulkheads 17 form a series of divisions of the required height to restrict the movement of water fore and aft, at any rate to such an extent as to permit the scuppers in any space on the non-flooded side of the bulkhead to cope with any minor leakage around the periphery of the bulkhead, which itself will have rubber flap seals against the ship's side structure and against flaps arranged on the casing, thereby further to restrict fore and aft movement of the water.

It is envisaged that, in way of each movable bulkhead, on the deck and on the top of the bulkhead when stowed, there shall be painted a 'No Go' stripe and vehicles, while they may drive across the stripe, must not be parked overhanging the stripe. Such an arrangement when loading a vessel provides no obstruction to fore and aft movement but, of course, requires some restriction of the longitudinal placing of vehicles, so that none overlap a painted stripe indicating a 'No Park' area.

This, however, need not produce any appreciable restriction of stowage capability in a vessel, the loss of stowage capacity, with reasonably careful anticipation on loading, being restricted to a very small percentage of the total lane metreage of the ship.

To ensure that the movable bulkheads do not jam, it is beneficial to avoid having a purely rectangular construction. The top and bottom surfaces may be parallel but the two ends, that is to say the two short sides of the lifting bulkhead, should be constructed in such a way that if any skew occurs in the vertical or lifting plane, the horizontal length of the bulkhead nevertheless remains constant. This can be achieved by making the bulkhead shape a portion of a circle (Figure 3). If a given length X is required for the bulkhead 17, then the bulkhead shape will be obtained from a circle of diameter X, with the top and bottom edges 22,23 of the bulkhead being horizontal chords of the circle symmetrically disposed about the horizontal diameter of the circle.The sum of the equal distances of the top and bottom edges from that diameter is, of course, equal to the total required depth of the bulkhead.

It has been found in practice that this arrangement is entirely satisfactory and that the bulkhead does not jam but travels smoothly vertically. Suitable rubber lap seals can be applied to prevent leakage around the ends of the bulkhead in way of the arcs 24. This arrangement has again been found to be satisfactory in tests.

During a passage of the vessel, the movable bulkheads 17 will be raised as a normal operation, just as the bow and stern doors of such a vessel are closed.

The bulkheads will increase the effective freeboard of the vessel at the bulkhead deck by the amount of the height of the bulkheads. No fore and aft access through the bulkheads will be necessary on passage but for crew convenience some means of fore and aft access over the bulkheads is desirable and this can be obtained by hinged flaps 25 on the bulkheads which, when dropped down, form steps up the side and down the other side.

In a convenient form, these flaps can be arranged so that when the bulkhead retracts they automatically fold up against the bulkhead, but when the bulkhead is raised from the stowed position they automatically drop down to form the steps . Alternatively, portable ladders may be provided, as is quite convenient; but the hinged flaps afford an ever present means of allowing crew passage over the bulkhead.

Figure 4 shows an embodiment of the invention having a series of fixed bulkheads 26 with vertically sliding roller shutter doors 27. Each end of each door is received in a channel 28 in a fixed portion of the bulkhead, sealing being effected by an inflatable seal or seals 29 in a groove or grooves 30 on one or both sides of the door. It will be seen that when uninflated a seal takes no load and all guiding of the shutter door is by the channel 28 itself, the seal 29 remaining out of contact with the door until inflated.

The roller shutter door 27 may be water-tight in itself, apart from its edges, but it is recognised that this is difficult to achieve and, more particularly, difficult to maintain in service due to wear, corrosion, damage, etc. Hence, a preferred feature is that the door is covered at either side of the steel rolling sections by a heavy plastic curtain which may be of polythene, neoprene or other suitable material. This curtain is attached at suitable intervals to the centres of the rolling sections but is not attached at the hinges between the sections. Thus, when the shutter is rolled up the two curtains are free to roll up with the steel or metal sections; and the entire shutter can be rolled up to the deck head and clear of the opening that is required below.The housing for the raised roller shutter and the depth of the tween deck height must be so arranged as to provide the necessary clear vehicle through height which generally will be of the order of 5 metres.

When the shutter is lowered the two curtains effectively seal the door completely so that it is water-tight in its own plane. Should water attempt to penetrate the bulkhead from one side or the other, in this arrangement there will always be a plastic seal across the face of the door facing the water that is being forced against the door and sealing the rolling leaf hinges.

Finally, the bottom of the door needs to be sealed and this may be effected by a variety of means, the simplest being a protruberant rubber neoprene or similar seal 31 set into the deck 32 (Figure 5) and against which the door rests under its own weight when in the lowered position. The seal extends along the opening of the door and there may be locking and dogging arrangements to hold the door down firmly against the deck and hence the seal. When the door is in the closed position, the bottom of the door may butt on the steel deck with the flat bottom surface of the door compressing the seal 31 and effecting a completely water-tight seal.

In another arrangement, the bottom seal 33 (Figure 6) can be lodged in a groove in the bottom of the shutter door, with a protuberant ground bar 34 on the deck along the door opening so that when the door is lowered into position the protuberant bar is squeezed into the seal in the underside of the door and effects a completely water-tight seal.

The shutter doors therefore provide means for sub-dividing the vehicle deck against the entry of water in the event of the margin line and deck edge being submerged in, for example, a collision. Should water enter longitudinally, as through open bow doors, the vessel would adopt a bow trim but would not sink or capsize as could be the case if the vehicle deck were completely unobstructed fore and aft.

The structural design of the roller shutter doors need not effect full water-tightness to a depth above the bulkhead deck of 5 metres. Generally, it will be sufficient to provide structural integrity to an immersed depth in the vehicle deck of perhaps 2 metres.

Claims (22)

CLAIMS:

1. A Ro-Ro vessel wherein, at vehicle deck level verticallymoving bulkheads are provided which can be lowered into a stowed position so that their upper edges are flush with the deck, thus forming a flat surface over which vehicles can move.

2. A vessel according to claim 1, wherein said bulkheads retract downwardly into slots or recesses in respective fixed bulkheads below the vehicle deck.

3. A vessel according to claim 1 or claim 2, wherein the moving bulkheads are raised by hoisting from the deck head above.

4. A vessel according to claim 1 or claim 2, wherein the moving bulkheads are raised by jacks pushing from below.

5. A vessel according to claim 4, wherein the jacks are housed in wells below the bottoms of the slots or recesses in which the moving bulkheads are housed when retracted.

6. A vessel according to any one of the preceding claims, comprising vertical means of adjustment of the moving bulkheads in the retracted position to ensure that their tops are level with the vehicle deck.

7. A vessel according to any preceding claim, wherein each moving bulkhead has a flat top plate provided with a flexible apron to rest on the vehicle deck when the bulkhead is retracted and prevent ingress to the slot or recess in which the bulkhead is housed.

8. A vessel according to any one of the preceding claims wherein the side edges of each moving bulkhead and/or the ship's side structure are provided with flexible flap seals to obstruct water flow past the sides of the bulkheads when raised.

9. A vessel according to any preceding claim, wherein the sides of each moving bulkhead are convexly arcuate to prevent jamming.

10. A vessel according to claim 9, wherein the bulkhead sides are arcs of a circle with a diameter substantially equal to the length from side to side of the bulkhead.

11. A vessel according to any one of the preceding claims wherein each bulkhead is equipped with steps or ladders for crew passage when the bulkheads are raised.

12. A vessel according to claim 11, wherein the steps are provided by hinged flaps on the bulkhead that fold up automatically when the bulkhead is retracted.

13; A Ro-Ro vessel wherein fixed bulkheads are provided at vehicle deck level which have openings to allow fore and aft vehicle movements and movable shutters for closing the openings.

14. A vessel according to claim 13, wherein the shutters are roller shutters operating in vertical channels in the bulkheads.

15. A vessel according to claim 13 or claim 14, wherein each bulkhead has a single wide shutter extending across all the vehicle lanes.

16. A vessel according to claim 13 or claim 14, wherein each bulkhead is provided with several separate shutters establishing individual vehicle lanes.

17. A vessel according to any one of claims 13 to 16, wherein inflatable seals are provided to seal the sides of each bulkhead shutter when closed.

18. A vessel according to any one of claims 13 to 17, wherein each shutter is covered at either face by a heavy flexible curtain of plastics material which rolls up with the shutter.

19. A vessel according to any one of claims 13 to 18, provided with transverse seals extending across the vehicle deck on to which the shutters descend.

20. A vessel according to any one of claims 13 to 18, wherein the underside of each shutter is provided with a flexible seal that is squeezed down on to a protuberant ground bar extending across the vehicle deck when the shutter is closed.

21. A Ro-Ro vessel provided with moving bulkheads substantially as described with reference to Figures 1 to 3 of the accompanying drawings.

22. A Ro-Ro vessel provided at the vehicle deck with fixed bulkheads with shutter doors substantially as described with reference to Figures 4 and 5 or 4 and 6 of the accompanying drawings.