Righting device for a water vessel

A device for righting a boat or other water vessel following a capsize. The device has an inflatable body which can be stowed in a collapsed state when uninflated. Compressed gas inflates the body following a capsize. The inflatable body has a flexible skin which forms at least first and second inflatable chambers. A valve arrangement causes the chambers to be inflated in a predetermined sequence. The first chamber securely mounts the valve upon the vessel. The second chamber is coupled to the first, supported by the first chamber when the device is deployed. Due to its buoyancy when submerged, the second chamber applies a righting moment to the vessel. The first chamber transmits this moment to the vessel. The staged inflation of the body alleviates its tendency to “pop up” to the surface before it is adequately inflated.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national phase of PCT application no. PCT/GB2013/050874 filed Apr. 3, 2013, which claims priority to Great Britain application No. GB 1206319.4, filed Apr. 10, 2012.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention is concerned with righting of boats following capsize and particularly with an inflatable device for that purpose.

(2) Desrciption of Related Art

Some boats are inherently unstable in an inverted condition and so tend to right themselves without assistance following a capsize. Others, such as sailing dinghies, can be righted by the crew while at sea. However some boats will float stably in an inverted condition following capsize and can be difficult to right. Rigid inflatable boats (“RIBs”) typically fall in this category. Clearly this poses dangers to the crew.

It is known in the art that such boats can be provided with what are referred to as self-righting devices—that is, devices which will right the boat without external intervention. An example of a vessel fitted with a self-righting device is seen inFIG. 1. This is a rigid inflatable boat (RIB)10of well known type, having a rigid hull12with inflatable tubes14extending along its gunwales on both sides. Boats of this general type come in a wide range of sizes and are used in many different roles. They may for example serve as military craft, as lifeboats, as tenders for larger craft etc. The example illustrated has an inboard engine but RIBs often use transom-mounted outboard engines. At the rear of the RIB10is a rigid arch16standing well above the hull and formed of metal tubing. An inflatable float18is mounted on a crossbar19at the top of the arch16. In normal operation the float18is deflated and stowed in a compact configuration (not shown in the drawing) on the crossbar19. If the RIB is overturned, by heavy seas for example, pressurised gas is supplied to the float18to inflate it. Clearly with the RIB10inverted, the float is submerged. When inflated the float18becomes buoyant and seeks a route to the surface. The rigid arch16serves as a lever through which the float18exerts a righting moment on the boat, causing it to roll back to an upright orientation.

The float18is inflated using a pressurised gas cylinder and associated valve which are not seen in the drawing.

While effective, self-righting devices of the illustrated type are not suited to all applications. In particular provision of the rigid arch16or some other raised, fixed structure through which the float18can exert the required leverage can be problematic. Where the RIB10is to be used as a gunboat, for example, it is important that the gun platform should have a full 360 degree view. The rigid arch16ofFIG. 1would potentially prevent targeting of objects behind the RIB10, which is undesirable. Another potential problem is that a boat used as a tender may need to be stored on the parent vessel in a space with limited headroom in which the arch16could not be accommodated.

One might imagine that the float18could be replaced with a larger inflatable float mounted on the deck or transom but in practice this proves ineffective. Experience shows that a float of this type tends, in use, to pop up to the surface beside the inverted boat before it is adequately inflated, making it incapable of righting the boat.

Prior art document U.S. Pat. No. 5,056,453 (Wright) describes a rigid inflatable boat with a self-righting apparatus in the form of an inflatable arch whose ends are each anchored to a respective tube of the RIB. That is, the arch spans the entire width of the RIB. It seems to be envisaged that the arch will be formed by a single inflatable chamber to be inflated following a capsize, and that this structure will naturally tend to inflate more rapidly on one side than the other so that its asymmetric buoyancy will determine the direction in which the boat rolls. Certain drawbacks are apparent. The arch depicted in the document appears to be mounted upon and integrated with the inflatable tubes of the RIB, potentially complicating the boat's manufacture. Storage of the deflated arch, which necessarily extends right across the RIB, may also prove problematic. It is not known how effective this design would be in practice.

Hence a need exists for an improved self-righting device for a boat or other vessel. It is particularly desirable that this device should have a low profile when stowed.

BRIEF SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there is a device for righting a boat or other water vessel following a capsize, the device comprising an inflatable body adapted to be stowed in a collapsed state when un-inflated, the inflatable body being provided with or adapted for connection to a source of compressed gas for inflating the body following a capsize and comprising a flexible skin forming first and second inflatable chambers, the device further comprising a valve arrangement for causing the chambers to inflate in a predetermined sequence in which the first chamber is inflated before the second, the first chamber being provided with means for securely mounting it upon the vessel whereas the second chamber is coupled to the first chamber and is arranged, when the body is inflated, to be supported by it, so that due to its buoyancy the second chamber is able to apply a righting moment which is transmitted through the first chamber to right the vessel.

By virtue of the sequential inflation of the first and second chambers, it is possible to establish an adequately rigid base or support for the second chamber before it is inflated, providing the buoyancy needed to right the vessel.

The present invention makes it possible to provide a wholly inflatable device which has a low profile when stowed and which is suitable for mounting at deck or transom level without any rigid upstanding support structure.

In accordance with a second aspect of the present invention, there is a method of righting a boat or other vessel following capsize, comprising

providing an inflatable body comprising a flexible, gas impermeable outer skin forming first and second inflatable chambers,

mounting the inflatable body upon the vessel and stowing it in a collapsed, uninflated state,

following a capsize of the vessel, supplying compressed gas to the first inflatable chamber and then; following inflation of the first inflatable chamber, to the second inflatable chamber to deploy the inflatable body and cause it to right the vessel.

DETAILED DESCRIPTION OF THE INVENTION

The righting device50seen inFIGS. 2 to 5has a body51which is wholly inflatable. That is, it does not have or require an upstanding supporting structure such as the arch16ofFIG. 1. When collapsed it forms a compact package which can be mounted at deck level or on a boat's transom. Thus for example if the vessel in question is a gunboat, the device need not impede the gun's line of sight along any direction. The inflatable body51is divided, as will be explained below, into multiple chambers whose sequence of inflation is controlled by an arrangement of valves through which the chambers are connectable to one another. By controlling the sequence of inflation in this way, and by suitable design of the body51, the natural tendency for the inflatable body to pop up to the surface prematurely is resisted.

In the illustrated embodiment the inflatable body51has a lower portion52of relatively small width54and depth56, and an oversized upper portion58. Due to its greater width and depth the upper portion contributes considerable buoyancy in operation and it will be referred to below as the float portion58. The lower portion serves to carry the float portion58and will for this reason be referred to as the support portion52. Note however that these designations are somewhat arbitrary—clearly every part of the body51, including the support portion52, contributes buoyancy when inflated and submerged, and each layer of the body51supports layers above it.

Note that throughout this document the terms “upper” and “lower” refer to the orientation of the righting device50when it is mounted on a vessel ready for use and that vessel is right way up, not capsized. Related terms such as “above” and “below” are to be similarly construed.

According to the illustrated embodiment the inflatable body51comprises multiple layers60ato60leach of which comprises an impermeable, flexible outer skin having upper and lower panels62,64joined by a perimeter wall66to form an internal plenum. Each layer60a . . . lcommunicates with its neighbour or neighbours so that gas can flow from one layer to another, although in some cases this flow of gas is regulated by an arrangement of valves. This aspect will be explained in more detail below.

In the illustrated embodiment the upper and lower panels62,64are coupled to one another at multiple points by an internal structure in a manner which contributes to the rigidity of the layers60a . . . l.This internal structure defines the separation of the upper and lower panels62,64and resists their natural tendency, when pressurised, to bulge away from one another. As a result the height of each of the layers60a . . . lis roughly constant across its width and depth and the upper and lower panels62,64are substantially flat and mutually parallel. The internal structure also prevents excessive shear of the upper and lower panels62,64relative to one another. The rigidity of the entire inflatable body51is greatly improved as a result. The layers' internal structure is flexible and does not prevent them from being compressed and folded for storage.

More specifically, the layers60a . . . lof the present embodiment comprise drop thread fabric which forms the aforementioned internal structure. This material is known to those skilled in the art of inflatables and is also referred to as drop stitch fabric. Upper and lower fabric panels are coupled to one another by an interlocking warp which may be created by a stitching process using multiple needles and which typically comprises a high density of fine threads, e.g. of polyester or nylon, running from one fabric layer to the other. The fabric is rendered gas impermeable by application of an outer skin, which in the present embodiment is of neoprene.

The layers60a . . . lform a stack with the upper panel62of one panel being secured, and more specifically being bonded, to the lower panel64of the layer above.

A further contribution to rigidity of the support portion52is made by straps arranged around it. In the illustrated embodiment there is a pair of straps66,68each of which forms a “U” shape when the device is inflated (seeFIG. 6in particular). The material forming the straps is flexible but has high tensile strength and tensile stiffness. Woven webbing is used in the illustrated embodiment. Tabs70of the same material are bonded to the support portion52at intervals up its height forming loops through which the straps66,68are passed (seeFIG. 4). A base portion72of each strap66,68(seeFIG. 6again) can be secured to a supporting structure (not shown) to securely mount the inflatable body51thereupon. Additional straps74are provided at each of the inflatable body's upright vertices and extend diagonally between anchor points on the support portion52and the float portion58to act as braces, further enhancing the body's rigidity when inflated.

It is desirable to provide some form of enclosure to store and protect the inflatable body51in its deflated and collapsed state when it is not in active use. This enclosure is not shown in the drawings and may take numerous different forms. For example the body could be stowed in a bag adapted to open or tear to release the inflatable body51as it inflates. An alternative is to stow the collapsed inflatable body51in a shallow box with a top panel forming a removable lid which will be pushed off as the body51inflates. The applicant envisages that a box of this type may be mounted on the upper edge of the transom of a RIB through suitably substantial brackets. The box itself would thus serve as a mounting and base for the righting device50.

A source of compressed gas is needed to inflate the body51and in the illustrated embodiment this takes the form of a pair of gas bottles78,80carried on opposite sides of the support portion52. The gas used in the present embodiment is a mixture of nitrogen and carbon dioxide. Inflation valves82controlling release of gas are in the present example manually operable. In the event of capsize a typical crew drill involves first having the crew congregate in the water, typically holding onto a line attached to the boat, before one of the crew activates the righting device, e.g. by pulling on a further line to open the inflation valves82, to deploy the righting device50and so right the vessel. In this way it can be ensured that crew are not in harm's way as the vessel is righted. However in principle the righting device50could use valves adapted to be released automatically upon immersion, e.g. by hydrostatic pressure and/or by sensing their own orientation.

The inflatable body51has multiple internal chambers controlled by an arrangement of valves which ensure that the chambers inflate in a predetermined sequence. The body's lower chambers, forming the support portion52, are inflated before its upper chambers, forming the float portion58. In this way an adequately rigid support is provided early in the inflation process. The larger float portion58is inflated only once this support has been deployed. The support portion52also forms a lever through which the float portion58can exert a moment on the vessel to right it.

Note that the term “chamber” is used herein to refer to an internal space of the inflatable body51through which gas can freely pass. This does not however imply that each such chamber is a simple plenum since, in the illustrated embodiment, each chamber is formed by multiple layers of the drop thread material. Within each chamber, neighbouring layers such as60aand60bcommunicate through an opening or openings in the upper panel of one layer60aaligned with similar opening(s) in the lower panel of the next layer60b.These openings are not seen in the drawings.

FIGS. 5ato 5eshow a sequence of steps in the inflation process. In each of these drawings only the parts of the body51which have been inflated are shown. This simplifies and clarifies the drawings and also reveals certain relevant internal details. The illustrated embodiment has five chambers91to95arranged one above another and these are inflated in vertical order, from the lowermost chamber91to the uppermost chamber95. Each chamber save for the uppermost chamber95communicates with the chamber above through a respective set of stage valves100to103which are normally closed and which open when pressure difference between the chamber below and the chamber above exceeds a predetermined threshold.

When opened to initiate the self righting process, the inflation valves82supply gas directly to the first, lowermost, chamber91and this consequently inflates first as seen inFIG. 5a.

When the first chamber91reaches a predetermined pressure, first stage valves100open to allow gas to begin to flow from the first chamber91to the second chamber92—seeFIG. 5b. Three first stage valves100are seen inFIG. 5abut a different number could be used. They are mounted in openings leading from the upper panel62of the top layer60dof the first chamber into the lower panel of the bottom layer60eof the second chamber. The stage valves100to103can be formed as normally closed one way spring controlled valves. Suitable valves are well known to the skilled person and need not be described herein.

The first and second chambers91,92together form the support portion52.

When pressure in the second chamber92becomes large enough to open the second stage valves101, inflation of the third chamber93begins—seeFIG. 5c. This is the first of the oversize chambers forming the float portion58.

In similar manner, third and fourth stage valves102,103then open in sequence to permit inflation of the fourth and fifth chambers94,95of the float portion58—seeFIGS. 5dand5e.

During or after this process of deployment, buoyancy of the body51tends to raise the stern of the vessel and, as the vessel turns to one side or the other, to exert a moment upon it, causing the vessel to roll back to an upright orientation.

Note that the stage valves100to103each serve to maintain a pressure difference between one chamber and the next. Hence following full inflation pressure is highest in the first chamber91and progressively reduces from the second to the fifth chambers92to94. This is desirable—it results in the lower parts of the body, which bear the greatest loads, being relatively rigid.

The aforegoing embodiment is presented by way of example and not limitation. Numerous variations of design and function are possible without departing from the scope of the present invention as determined by the appended claims. For example while the illustrated embodiment uses five individual inflatable chambers, the actual number of chambers may vary according to design criteria, including for example the size of the vessel to be righted. The shape of the inflatable body is capable of considerable modification. The skilled person will recognise that the valve arrangement providing for sequential inflation of the chambers could take any number of different forms.