GB2293796A - Safety improvements for vehicular ferries and other vessels. - Google Patents

Abstract

Inflatable bags 10 - 15 are so constructed, arranged and anchored within the hull of a ship that when inflated they form barriers to the bulk movement of flood-water within the cargo space or other large, enclosed space within the ship, direct the flow of flood-water away from the sensitive areas where its presence is most detrimental to stability, occupy a substantial fraction of the volume of such sensitive areas and contribute to preventing the shifting of cargo. A particular application is to RORO ferries wherein rows of bags 10 are arranged both longitudinally between vehicle lanes 11 and transversely. <IMAGE>

Description

SAFETY IMPROVEMENTS FOR VEHICULAR FERRIES AND OTHER VESSELS Ships for the carriage of motor vehicles are commonly designed so that the vehicles can be driven on at the port of embarcation and driven off again at the destination, and are thus often called roll-on, roll-off or RoRo ferries. They are subject to peculiar dangers: the danger which is of particular concern herein arises from the typical arrangement of a large, flat, enclosed space to accommodate the vehicles which constitute the cargo. Access to this vehicle space is commonly by way of ramps and doors at one or both ends, but internally it is usually undivided and unencumbered, to make the movement and stowage of the cargo easier.Any vessel having a similar arrangement is similarly at risk, whether or not the vessel is intended for the carriage of motor vehicles: the description, understood as being appropriately modified for the circumstances, applies equally to such other vessels, and the phrase 'vehicle space' is to be understood as referring to any large, open space in such a vessel also.

If by whatever means a substantial quantity of water reaches the vehicle space, it forms an unstable moving mass, liable to surge from side to side and end to end of the vehicle space as the ship manoeuvres or responds to wave action. The sudden transfer of many tons of water to one side of the ship is sufficient to cause the ship to tilt or list to that side, and this condition may be irreversible. Several ships and hundreds of lives have been lost in accidents arising essentially from this essentially trivial cause. Commonly, also, the cargo in the vehicle space is unsecured or insufficiently secured, such that it shifts as the consequence of a severe list and thus contributes to making the list irreversible.

Bulkheads or barriers, might be installed to prevent this bulk movement of water, but if fixed would inevitably impede loading and unloading of the cargo, and if movable will probably prove heavy, cumbersome and expensive, or not strong enough. The present invention is of a novel means to prevent or minimise such bulk movement of water, a means which does not involve the installation of conventional barriers or bulkheads to subdivide the vehicle space. However, the means described herein could be used in combination with other means of improving the safety of RoRo and similar vessels, and specifically with either fixed or movable barriers or bulkheads, if such were to be installed.

Several patents exist and in other respects it is established art, to provide inflatable bags within inboard spaces of either small or larger vessels with a view to prevent sinking after flooding by provision of reserve buoyancy, or to improve static stability after flooding, or to expel water from damaged or flooded compartments of a vessel. The present invention differs in principle from such arrangements.

Many proposals have been made to improve the stability of a flooded RoRo ship by means of inflatable bags ('sponsons') outside the hull of the vessel. The present invention differs in principle from such arrangements.

DESCRIPTION This invention chiefly consists in means to improve flooded stability by restricting and directing the bulk movement, and the accumulation, of flood-water within a large vehicle or cargo space; comprising inflatable bags attached to one or more of the fixed structures that form or sub-divide such a space, such as the deck, sidewalls, bulkheads and deckhead.

Figures 1 to 4 show cross sections of fully-inflated bags in a typical situation, namely attached to the deck or floor of the vehicle space. In each case it is to be understood that the attachment to the deck or floor is over substantially the whole length of the bag.

Figure 1 shows a bag 1 having approximately rectangular cross section, though the walls and top bulge out under internal pressure. The bag is attached to the deck 2 over essentially the whole of its width. Figure 2 shows a similar bag attached to the deck 2 only by a narrow flange 3.

Figure 3 shows a bag of approximately elliptical cross section attached to the deck 2 by a flange 3.

Figure 4 shows a bag of roughly circular cross section which itself is not attached to the deck, but which in the inflated condition is constrained by a flexible sheet 4 attached to the deck 2 near each side of the bag at locations 5.

Figure 5A shows a bag such as that in Figure 1, but in a deflated condition and lying in a well 6 below the principal level of the deck 2, under protective flaps 7, and attached to the floor 8 of the well 6. Figure 5B shows the same bag in the process of inflating and pushing the protective flaps aside: in the Figure the flaps 7 are shown as paired and attached to the deck 2 by hinges, but these are not essential features. Bags of other cross section and other designs may equally be installed in such protective wells.

Figure 6A shows a bag such as that in Figure 4, but deflated and lying underneath a hollow protective hump 9. Figure 6B shows the same bag in the process of inflating and throwing aside the protective hump: in the Figure, the hump is shown as constructed in a single piece across its whole width and not attached to the deck in any way, but these are not essential features. Bags of other cross section and other designs may equally be covered by such hollow, movable, protective humps.

Bags at the sidewalls or deckhead (see below) or in other untypical locations may have special shapes and special methods of attachment not shown in Figures 1 to 6, or in any Figure.

Figure 7 is a plan view and Figure 8 is a cross section of a typical vehicle space, showing how rows of bags may be arranged longitudinally 10 between the vehicle lanes 11 (whether occupied by vehicles or not), or transversely to the long axis of the ship 12, or 13 between the outer vehicle lanes and the sidewalls 14, or 15 higher up and especially at the angle 16 between the sidewall 14 and the deckhead 17.

Figures 9A and 9B show a plan view of one possible arrangement by which a one-way valve operation might be provided between adjacent bags within one row of bags. Bags la and ib, envisaged here as being of the type shown in cross section in Figure 1, are secured to the deck along essentially their whole length, but not to each other or not over their whole height.

Only a part of the length of each of the bags la and ib is shown in Figures 9A and 9B. As shown in Figure 9A, water 18 may pass between the bags la and lb under the influence of gravity or momentum, by displacing the flap 19 attached to bag ib, but reverse movement is prevented by closure of the flap as shown in Figure 9B. Similar arrangements may be envisaged for bags of other cross section or other designs.

According to this invention, inflatable bags 1 are secured most typically to the deck 2 of the vehicle space or within protective wells 6, and are closely-spaced in complete or integral rows, arranged longitudinally 10 between the vehicle lanes 11 and also transversely 12. Each bag may be attached to its neighbours. In these typical situations the bags are so arranged as to form, when inflated, an effective barrier to the bulk movement of water. In normal operation of the ship each bag is in deflated condition (Figures 5A, 6A) and may lie below the level of the deck 2 in a specially designed well 6 under protective flaps 7 at the level of the deck 2 or may be otherwise protected from random mechanical damage (see for example Figure 6A). The bag is attached along a large part or the whole of its length to the deck 2 or to the floor 8 of the protective well 6 in which it lies if that option has been adopted. Upon inflation (Figures 5B, 6B) each bag swells to a shape which may be roughly rectangular or roughly circular or elliptical in cross-section (Figures 1 to 4), or of a specific shape tailored to its particular location (as exemplified in part by 13, 15), under an internal pressure of several bar, but remains attached to the deck 2 or well floor 8 so that water is impeded from passing under the bag, either from side to side or longitudinally with reference to the axes of the ship, according to whether the particular bag forms part of a longitudinal 10 or a transverse 12 row respectively. In particular, bags in the longitudinal rows 10 would impede the shifting of cargo as the ship rolls or lists.

The bags may be so arranged and constructed (Figures 9A, 9B) as to form a series of one-way valves which allow water to pass relatively easily towards the central area 20 of the vehicle space whilst preventing the flow of water towards the side walls 14 or the ends 21 of the vehicle space. To explain further the practicability of such a valve as is illustrated in Figures 9A and 9B, the two bags concerned may be attached to each other at deck level 2 and at the top, and even at one or more other points on their adjacent faces, yet still allow the flow of water between them as shown in Figure 9A, provided that the links between bags la and lb, especially links above the level of the deck 2, are of a sufficiently flexible and elongated nature.

Other bags 13 may be attached to the side walls 14 of the vehicle space, between the outer vehicle lanes and the aforesaid walls 14 and yet other bags 15 to the deckhead 17 especially at the sides (see Figure 8).

The above description of the mode of attachment of the bags is not applicable in all particulars to the bags 13, 15 in these locations 14, 17 and the considerations affecting integrity or completeness and watertightness of the rows do not apply to these bags 13 and 15 in the same way or to the same degree as applies to bags in the typical locations 10 and 12, as will be clear to those skilled in the art. Throughout, the description given applies primarily to individual bags and rows of bags in the typical locations 10 and 12, between the parked vehicles constituting the cargo, and is to be understood as modified appropriately when referring to bags in other situations.For brevity and clarity, the description implies that each bag is of elongated shape having a definite horizontal or approximately horizontal long axis (which may be near parallel to or transverse to the long axis of the ship). In practice however, and certainly in certain special locations, the bags may have other shapes (e.g. cubical or as exemplified by 15), and the description is to be understood as modified appropriately so as to include these.

A moderate or even a considerable number of smaller bags is preferred to a few large ones for reasons of ease and standardisation in manufacture, mechanical strength, space restrictions and diminished consequences in the event of failure of one or a few bags. The material of the bags is required to be flexible, essentially gas-tight, yet tough, and more so if a role in preventing shifting of cargo is envisaged. The dimensions are appropriate to the location of each, but taken all together and with reference especially to the bags 13, 15 at the sides of the vehicle space, they occupy, when inflated, a significant proportion of the most critical parts of the volume of the vehicle space, as shown to be required by calculations or computer modelling of stability in flooded condition, so that they have an effect over and above that of mere barriers.

Typically, but depending on the dimensions of the ship concerned, those attached to the floor towards the centre of the vehicle space might be from 1 to 3 metres high when inflated, but larger and in particular taller bags 13, 15 are appropriate towards or at the side walls 14 of the vehicle space and, if installed, at the deckhead 17.

The provision of gas to inflate the bags may be by any of several possible means well known in the art, but it is essential that rapid inflation [seconds to minutes] is available, and the supply of gas must be such as to be not necessarily dependent on the main power supply of the ship. Gas might be supplied by pipes 22 though such a means of supply is not the only possibility. It is to be understood that pipes or other means of gas supply are present at one or more points along the length of each bag, whether illustrated or not. Inflation may be controlled automatically by sensors capable of reacting to the presence of water or only of salt water in the vehicle space, or to other conditions, or manually, or by remote control. In the latter two types of operation, inflation might be carried out in anticipation of trouble or at the first sign of trouble.

The advantages of the invention are apparent in that when inflated the bags serve to: 1] Obstruct bulk movement of water within the vehicle space.

2] Avoid mal-distribution of gravitational forces by taking the place of water which might otherwise accumulate at the most sensitive places, namely the extreme sides or ends of the vehicle space, so that the bulk of water which may have reached the vehicle space is forced to lie more centrally. (This role of the bags is viewed as both conceptually and in practice quite distinct from merely the provision of supplementary buoyancy or reserve buoyancy.] The use of the 'one-way valve' option would enhance this role.

3] Improve the flow of water to the pumps, since the bags could be so arranged in detail (not illustrated) as to constitute effective, temporary, accessory conduits, leading to the sumps.

4] Prevent or limit the shifting of cargo.

5] Provide some degree of extra or reserve buoyancy in the case of complete swamping of the vehicle space.

6] Though the total volume occupied by the bags, and hence the total amount of enclosed buoyancy reserve, would not be great, they, and especially those 13, 15 located at the sides 14 of the vehicle space and at the deckhead 17, could contribute critically to ensuring that a fatally damaged or flooded vessel eventually sank on an even keel, i.e. foundered rather than capsized (the ultimate disaster).

7] Installation on existing ships is possible, though in such a case it will often not be possible, or not cost-effective, to instal the bags in wells below deck level.

Claims (1)

1] Means to improve the flooded stability and diminish the risk of capsize or sinking of any vessels, but especially vessels in which there is a large, substantially flat, enclosed cargo space or vehicle space or any other such space, by preventing or restricting the bulk movement of flood-water within the cargo space and the accumulation of flood-water in areas where its presence is particularly detrimental to stability; characterised in that inflatable bags attached to the deck or floor of the cargo space, and if desired also to the sidewalls, any bulkheads, and deckhead of the cargo space, are so arranged that when inflated the bags obstruct the bulk movement of flood-water and/or occupy a substantial fraction of the volume of those areas where the accumulation of flood-water is most detrimental to stability, especially areas at the sides and ends of the cargo space.

2] Means according to Claim 1 in which provision is also made for the bags to be so constructed and arranged as to constitute oneway valves that direct the overall movement of flood-water away from those areas where its presence is most detrimental to stability, such as towards the centre of the cargo space.

3] Means according to Claims 1 or 2 when combined with the installation of fixed or moveable barriers or bulkheads or other means to prevent or restrict or direct the bulk movement of flood-water, or with other means known in the art to achieve the objectives of the invention 4] Means according to any of Claims 1 to 3 in which some or all of the inflatable bags serve also to prevent or limit the undesirable movement or shifting of cargo.

5] Means according to any of Claims 1 to 4 in which some or all of the inflatable bags serve also to provide reserve buoyancy.

6] Means according any of Claims 1 to 5 in which some or all of the bags are installed in wells below the level of the deck of the cargo space, and are thus or otherwise protected from random damage whilst uninflated.