GB2429681A - Inflatable device with reduced compressed inflation gas requirement - Google Patents

Abstract

An inflatable structure, such as a liferaft, has inflatable members 201, 202, 203 and a cover member 206 that together define a chamber. As the members are inflated, the volume of the chamber increases. A one-way inlet valve 212 allows ambient air into the chamber as the volume increases to provide a pressurised chamber when inflation is complete. The inflatable structure may be housed in a collapsed state within a container, the inflatable members being inflated on release from the container. A reduced amount of compressed gas is required to inflate the entire structure since the chamber is inflated with ambient air.

Description

INFLATABLES

The present invention relates at its most general to inflatable structures and systems.

Inflatable devices have long been used in safety equipment, and since World War 2 the development of inflatable escape slides, inflatable liferafts and lifejackets and many other inflatable safety devices has been prodigious.

Many inflatable safety devices utilise a compressed stored gas source typically carbon dioxide - which, under compression, becomes a liquid phase. Such compressed gas is typically stored in a metal cylinder, attached to the inflatable structure. When the device is needed, e.g. in an emergency such as a ship sinking, or a person falling into the water, the compressed gas is released - typically by opening a valve in the gas cylinder or, more recently, by using a spring-loaded puncturing device which pierces a sealing disc in the end of the cylinder. This releases the compressed gas into the liferaft or lifejacket or other inflatable structure and thereby causes its inflation to a pie-determined design volume and inflation pressure. This has proved to be a most effective means of inflation and typically a liferaft can be fully inflated in less than a few minutes and a lifejacket within a few seconds. As larger structures were developed, such as escape slides, greater volumes of gas and consequently greater inflation speeds were required and systems using stored banks of compressed gas (typically nitrogen) were developed.

According to a first aspect of the invention, there is provided an inflatable structure comprising at least one inflatable member and at least one cover forming together an enclosed chamber, and inflation system for inflating the inflatable member, said inflation increasing the volume of the chamber and an inlet valve being provided for allowing air to pass into the chamber as the inflation member is inflated.

According to a second aspect of the invention there is provided an inflatable device comprising an inflatable support structure which when deployed supports a flexible outer envelope, the assembly of the support structure and the outer envelope being collapsible and the device further comprising a container within which the assembly is able to be stowed in a collapsed state, the device further comprising a release arrangement for releasing the assembly from the container and the outer envelope having at least one port for inlet of ambient air, so that following release the outer envelope is expanded by the support structure, air being consequently drawn into the outer envelope.

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figurcs la, lb and Ic depict an impact protection system not according to the present invention in side, plan and sectional views respectively; Figure 2 is a detail view of the same impact protection system, viewed from beneath; Figure 3 is a sectional view of a guillotine device used in the same impact protection system; Figure 4 illustrates the same impact protection system in use; Figure 5 illustrates an impact protection system embodying the present invention in use; Figure 6 is a plan view of the Figure 5 impact protection system; Figures 7 and 8 are sectional views of the impact protection system of Figures 5 and 6; Figure 9 is a section through a drop thread" type of double-walled material; Figure 10 illustrate a helicopter floatation device embodying the present invention, a and b being side views of the device before and after its deployment respectively and c being a section through the deployed device in a lateral plane: Figures 1 la and b illustrate a righting device fitted on a boat, a showing the device prior to deployment and b showing it in use; Figure 12 is a schematic cross-section through a liferaft formed by a sidewall of inflatable tubes and first and second covers, Figure 13 is a similar view to Figure 12 but showing a person in the liferaft and a canopy, Figure 14 is a perspective view of a second form of liferaft in an inflated condition and with an upper cover removed, Figure 15 is a plan view from above of the liferaft of Figure 14, Figure 16 is a side view of the liferaft of Figures 14 and 15 in a packed collapsed deposition and deployed on water.

Figure 17 is a similar view to Figure 16 with sidewalls of the liferaft partially inflated, and Figure 18 is a similar view to Figure 17 showing a cross-section of the liferaft fully inflated.

The embodiments to be described with reference to Figures 1 to 4 are not in accordance with the invention but are included to illustrate a system of the type to which the invention can be applied.

The impact protection system of Figures 1 to 3 is intended for fitting to a land vehicle, particularly a road vehicle, to prevent impact injury to pedestrians in the event of collision. Protection for pedestrians in the case of a frontal impact is required now by Legislation. This invention is an economical alternative to the "crumple zones" which motor vehicle manufacturers typically design into new vehicle designs to meet these requirements.

The system comprises a vehicle bumper 12 comprising a restraining container formed between a cover 14 and a recess in the front of the motor vehicle. The cover 14 is formed in this embodiment of woven fabric, for example Keviar, the type of material used in making bullet-proof vests. This material is extremely strong and resistant to cuts and puncturing without being so rigid as to cause injury to the pedestrian or occupant. The cover 14 is retained in position by means of a lacing system 18 using a very strong cord, which may for example be of Kcvlar. A lace 20 is led back and forth between holes - formed e.g. as eyelets - in the cover and the structure or the vehicle (Figure 1). Within the container is an inflatable envelope formed as an airbag 22, which is able to be pre-pressurised after its placement within the cover through a valve and supply tube 24 accessible from the exterior. The cover and its associated lacing retain the airbag 22 in a collapsed state despite its internal pressure. Once airbag 22 has been pressurised to a pre- determined pressure then the system is ready for use. Sensing devices 26, 261, which can be connected to a "logic circuit", serve to trigger release of the airbag.

If one of the sensing device 26 detects an impending impact, it then triggers release of the cover.

The envelope - in the above example the airbag 2 - is pre-pressurised, for example by means of a compressor, in order to achieve a pressure much greater than that required following its deployment. For example, if the structure were an inflatable airbag of 100 litres volume (V2) and its design (post deployment) pressure were 0.5 psi (P2) and the volume when it while inside the container were 5 litres (V 1), then VI xPl=V2xP2 Thus, 5 litres x P1 = 100 litres x 15 psi (G) Thus P1 = 150 psi (absolute) P1 = 135.5 psi (G) Therefore the inflatable structure would be pressurised to 135.5 psi inside the container. When the cover is released then it will immediately expand to its design volume (100 litres) and design pressure 0.5 p.s.i. (G).

To cause release the lace 20 holding the cover closed, which is under considerable tension, can be cut by a small guillotine device 28 depicted in detail in Figure 3.

The lace 20 is led through a device housing 30. Within the housing 30 is a piston 32 having a blade 34 which faces toward the lace. Application of electric current causes a small pyrotechnic charge 36 arranged adjacent the piston within the housing 30 to ignite, driving the piston 32 forward to cut the lace 20. One such guillotine device is provided in the illustrated exemplary embodiment but two or more such devices could be provided to cut the lacing at intervals along its length.

The lace 20 is under substantial tension when cut, and therefore rapidly opens to allow the airbag 22 to expand to its design pressure and volume as depicted in the Figure 4.

An alternative embodiment, lacking the guillotine 28, has a lace 20 formed from cord of a chosen breaking strength. In this case deployment of the airbag 22 is initiated by ignition of a small gas generator pyrotechnic charge 38 which is located inside the airbag 22 (Figure 2 shows the gas generator 38 as well as the guillotine 28, although practical embodiments would typically have one or the other). The additional heat and pressure rapidly created by the gas generator 38 increases the pressure inside airhag 22, causing the lace 20 to be stressed beyond its breaking point. The lace 20 breaks and allows the airbag 22 to be released.

This second means of release has some benefits over the type device. These are: - 1. It may be more reliable 2. II may be more rapid 3. In extremely cold air temperatures the gas volume and pressure in airbag 22 prior to deployment will be reduced, which can be detrimental to the inflation speed and pressure. The effect of using the gas generator pyrotechnic charge 38 as a means of release is that this additionally heats the pressurised air and the system will therefore be equally effective whether used in extremely hot or cold environments.

Another method of ensuring constant inflation speed through a range of ambient temperatures is to fit a heating element (powered by the vehicle) inside the cover.

This maintains the pressurised gas inside airbag 22 at an acceptable temperature regardless of the ambient temperature.

Airbag 22 (or indeed other inflatable bodies in other embodiments of the present invention) may be inflated using a compressor such as those used to inflate vehicle tyres. Pressure can be checked and topped up whenever needed by the owner or during a service etc. A pressure sensor 40 serves to measure pressure in the airbag and a warning is provided to the driver if the pressure is below a given value.

Another means of pre-pressurising the device is to have it constantly "topped up" by a compressor pump driven by the vehicle's power supply and feeding air through a conduit 42 communicating with the airbag or other inflatable envelope.

Thus even if there is a small leakage in the system, it can be maintained at all times above a given pressure.

Some inflatable safety systems, such as vehicle airbags, work on the principle that the impact of a person coming into dynamic contact with the inflatable causes it to be deflated. This process of deflation deaccelerates the impacting body and dissipates the body's kinetic energy at the same time as it slows the body down. In this case, almost as soon as the inflatable structure reaches its operating and design pressure. it needs to be able to begin to deflate on impact. In vehicle airbags this may be achieved (1) by using a porous material for the bag; (2) by means of a bag with a number of holes in it; or (3) by means of pressurerelieving valves fitted to the bag. Airbags, or inflatable envelopes for other purposes. of any of types 1-3 may be used in embodiments of the present invention. In some such embodiments the envelope itself is placed within a pre-pressurised airtight enclosure to prevent it from deflating. In the embodiment illustrated in Figure 2 this enclosure takes the form of an airtight bag 44 which is sealed around the airbag 22 and serves to hold the pressure until the outer cover 14 is allowed to open, at which time the airtight bag 44 bursts open and releases the airbag 22.

This type of arrangement can be useful even for inflatable structures which are not required to deflate on impact, since it is sometimes difficult to make inflatable structures totally airtight. For example it is difficult to make totally airtight structures using double wall type materials etc., and it is difficult to achieve total air tightness at very high pressures. The outer airtight bag 44 ensures that pre- pressurisation is sustained. In order to ensure that the volume inside the inflatable envelope such as airbag 22 completely fills the space inside the cover 14, a soft but open cell foam can be put inside the inflatable.

The present invention utilises ambient air to fill part of the inflation volume and can be used with a system of the kind described above with reference to the drawings. Figures 5 to 9 depict an embodiment of this type, in the form of an impact protection system similar to that of Figure 2 to 4. As with that earlier embodiment, the present example has an inflatable structure 45 initially pre- pressurised within the inflatable bumper and its cover. The inflatable device is formed by a number of inflatable panels 46 used to create the structure. These are made typically from a double-wall "3-dimensional" material of the type illustrated in Figure 9. Such materials are known in themselves. Two gas impermeable outer layers 48, 50 are connected by drop threads 52 whose length thus determines the spacing of the outer layers when the panel is inflated. The overall shape of the inflatable 45 is formed by the' panels 46 when inflated. These panels typically have a gauge of 5 to 7.5 centimetres. This type of material, when inflated, is very rigid for a given volume and pressure when it is compared to other inflatable type materials which are just a single layer. The drop threads would be damaged by the force of hot gas from conventional gas generators used for airbag inflation, but such problems are avoided by virtue of the present invention. The panels 46 are mounted on the vehicle and are placed within an outer envelope 54. It is fitted with large one-way "flap valves" 56 arranged to admit air to its interior. The panels 46 in this particular embodiment are all intercormected by air passages, such that they are all subject to the same pre-pressurisation. As in the earlier embodiment the inflatable envelope comprising the panels 46 is pre- pressurised inside a cover which on release allows the panels to rapidly open out to their design shape and pressure. As the panels unfold and expand outwards they pull the outer envelope 54 out to shape and in doing so create a sub-atmospheric pressure inside the outer envelope 54. Ambient air is therefore drawn into the outer envelope 54 through the one-way flap valves 56. Thus, once to design shape, the structure consists of a number of panels 46, which are above atmospheric pressure, with an airspace between them which is at atmospheric air pressure (0 psi g). The material of the outer envelope 54 is porous or has a number of holes in it or could be fitted with relief valves such that as the pedestrian is impacted by the structure it deflates, thereby cushioning the pedestrian's impact and dissipating the energy. reducing the risk of injury to the pedestrian etc. In all other respects this method of creating the inflatable structure can be the same as that depicted in Figures 1 to 3. It can also be used to create an interior occupant restraint system. The main advantage of this second embodiment of the invention is that the volume of pre-pressurised gas for a given pre-pressure is considerably less than that required by the type of structure in Figures 1 to 4. The "inflatable bumper" can therefore have a smaller profile and volume according to this aspect of the invention. There are also o advantages in creating a better contoured surface for the area that will be the impact area - e.g. a flat, or even concave surface can be created rather than a round shape, which has benefits on pedestrian impact.

The invention is also applicable in marine and aeronautical environments. A lifejacket or liferaft or a floatation device of any sort can be made to "inflate" by using the pre-pressurisation principle, being retained in a compact pre-pressurised condition until needed in an emergency. On release, by means of any of the types of release arrangement described above, the inflatable rapidly expands to its design volume and pressure and therefore provides the necessary buoyancy for floatation support of people or equipment.

Emergency inflatable floatation devices carried on the underside of helicopters.

which support the helicopter if it "ditches" into water, may be constructed in this manner, as too may "self-righting" floatation devices for fitting to a "self-righting" frame mounted on a lifeboat to "reright" the lifeboat in the event of it capsizing.

Such devices are again be constructed in such a manner that they draw in ambient air when released. Without this facility the result of compression of large gas volumes into a compact package suitable for storage e.g. on a helicopter could be excessive internal pressure, with the result that release of the inflatable would be "explosive" and could damage and de-stabilise the helicopter or lifeboat etc., or would be dangerous to the person or persons activating the device. If the device were a lifejacket then such an explosive force could injure the person wearing it.

In some such embodiments an inflatable "frame" or structure is inflated to a pressure greater than its design pressure and is retained inside a strong cover until required in an emergency. When the frame or structure is released, it unfolds to take up its design volume, pressure and shape. The frame or supporting structure is covered by an airtight flexible bag, such that when it takes up its design shape, air at atmospheric pressure is drawn into the interior of the airtight material through an opening. This opening could be a one-way valve such that when the structure is fully deployed the volume can be maintained even in the event of immersion. The speed at which the structure inflates is controlled by the size of the opening.

A helicopter floatation pod 76 is illustrated in Figures 1 Ia, 1 lb and I ic and is mounted at the underside of helicopter 78 by means of a rigid support 80, ready to be inflated in an emergency (for example in the event of "ditching" onto water).

The system can be "charged" by "pre-inflating" the device by using a compressed air line, for example the same airline used to inflate the helicopter tyres etc. It comprises an inflatable envelope 82 which is initially (Figure 1 la) contained within an airtight, bag-like enclosure 84 and is maintained in a collapsed state within a container formed by a releasable cover 86 secured to the rigid support 80 through lacing. The inflatable envelope 82 forms, following its deployment, a frame 90 supporting an outer envelope 92 containing, in a volume 94, air at atmospheric pressure drawn in from the surroundings. The frame 90 can be made by way of a tubular structure or by using "double-wall" material of the type illustrated in Figure 10. The volume within the frame 90 is prepressurised prior to deployment. An activation device is provided, for initiating deployment, which can be manual or automatic. An automatic device can be triggered by immersion.

The activation device triggers release of the cover 86. Similarly to previous embodiments, release may be caused by cutting the lacing, e.g. using a guillotine device, or by using a pyrotechnic gas generator, or by a small compressed gas charge. The "frame" 90 then opens out to its design volume and shape, causing the outer envelope 92 to expand and draw in ambient air through a rigid or supported tube 96 which connects the interior 94 of the outer envelope to an opening to atmosphere which is above the water. Typically this opening is inside the helicopter where it would not be immersed.

The device may if desired be charged", i.e. pre-pressurised ready for use, only when the item needs to become operational, for example as part of pre-flight preparation. It can thus be discharged for storage.

Figures 1 la and 1 lb depict a lifeboat 100 with a device 102 for righting a lifeboat following capsize. The righting device comprises a structure 104 projecting upwardly from the lifeboat hull and supporting a buoyancy module 106 constructed in accordance with the present invention. The buoyancy module comprises a container formed by rigid upper and lower panels 108,110 held together through an arrangement 112 which may be a lacing system of the type previously described or may instead comprise quick release bolts. Alternatively the rigid panels could be replaced by a strong flexible cover as in previous embodiments. Within the container thus formed is the inflatable envelope 114, which may be formed as an inflatable frame as previously described with reference to Figures lOa, lOb and lOc, or may be a tubular structure or a series of tubes which are pre-pressurised inside the container. Similarly to the example described with reference to Figures lOa, lOb and lOc, an outer envelope 116 contains the frame. As the frame expands a pressure less than atmospheric pressure is created in the outer envelope 116 and air then enters this space at low pressure through tubes 118 connected to the interior of the outer envelope. To the exterior of the bag the tubes 118 extend to a point well above the water surface when the boat is capsized. In the present embodiment, the tubes 118 form the support structure 104.

In use, the buoyancy of the module 106 following its deployment causes it to rise to the surface and so to reverse the capsize. The device can be reactivated by deflating the inflatable structure and recharging the system again from a compressor or other compressed gas source.

The devices described above with reference to the drawings can also use an external compressed gas cylinder in order to inflate the "frame" rather than pre- pressurising the "frame" as previously described. In this case the same overall buoyancy volume can be created from a much smaller compressed gas charge, than if the inflation did not use the air being drawn in from the exterior of the structure. This means that the weight and packed size of the compressed gas cylinder is very much reduced. Some examples of embodiments using this principle will now be described with reference to the Figures 12 to 18.

The liferaft of Figures 12 and 13 is shown in a deployed inflated condition and comprises a sidewall 200 formed by first, second and third superimposed inflatable tubes 201, 202, 203. The tubes 201, 202, 203 are inflated by an inflation system 204 and, when inflated, form a closed shape such as a circle. The tubes 201, 202, 203 may be made from any suitable material such as rubberised fabric and are assembled by conventional methods.

The floor of the liferaft is formed by a first cover 205 and a second cover 206.

The first cover 205, which may also be formed of a rubberised fabric, is attached at its periphery to the outer surface of the first tube 201. A second cover 206, which may also be formed of a rubberised fabric, is attached at its periphery to the outer surface of the third tube 203. The second cover 206 has a greater area than the first cover 205 and is connected to the first cover 205 by three connector strips 207, 208, 209. These strips 207, 208, 209 constrain the second cover 206 to form an annular downwardly sloping outer portion 210 and a flat central portion 211.

The connector strips 207, 208, 209 are provided with respective holes to allow the free passage of gas around the chamber formed by the sidewall 200 and the covers 205, 206. A one-way valve 212 is provided in the outer portion 210 for a purpose to be described below.

In use, the liferaft is packed with the first, second and third tubes 201, 202, 203 deflated and the tubes 201, 202, 203 and the covers 205, 206 and the inflation system 204 in a container (not shown). When the liferaft is required for use, the liferaft is removed from the container. This may be manual or may be by actuation of the inflation system 104 to commence inflation of the tubes 201, 202.

203 and so burst the liferaft from the container. Alternatively, the container may open automatically on being deployed in water.

The inflation system 204 then inflates the first, second and third tubes 201, 202, 203. If the inflation system 204 has not already been activated to deploy the liferaft from the container, this may be done automatically or manually by, for example, pulling on a lanyard.

As the first, second and third tubes 201, 202, 203 inflate, the first and second covers 205, 205 are separate and the volume of the chamber defined by the tubes 201, 202, 203 and the covers 205, 206 increases. As a result, ambient air is drawn into the chamber through the valve 212. Accordingly, as all the tubes 201, 202, 203 are inflated, the chamber is also filled with ambient air so forming a cushioned floor to the liferaft. As seen in Figure 13, an erectable canopy 213 may be provided to protect an occupant of the liferaft.

The use of a chamber whose volume expands during deployment to drawn in air has a number of advantages. First, it allows the volume of air in the inflation system 204 to be less than would be the case if the system also had to inflate the floor. This decreases the weight of the system. In comparison with liferafts where the floor is filled with air using a manual pump, it provides automatic deployment of the floor.

The second liferaft of Figures 14 to 18 is formed by first and second principal inflatable tubes 220, 221 shaped to form a liferaft with parallel sides and first and second pointed V-shaped ends forming a prow and a stern. A third inflatable tube 222 extends along the sides and around the first end to provide additional height and a fourth inflatable tube 223 also extends around the first end to provide the prow. In addition, two parallel struts 224 extend across the interior of the liferaft between respective positions on the first tube 220 at one side wall and corresponding positions on the first tube 200 at the other side wall. The side walls 220, 221, 222, 223 and 224 may be formed as described above with reference to Figures 12 and 13.

A first cover sheet 225, which may be formed of a rubberised fabric, is connected to the first tube 220 and extends over the enclosed spaced bounded by the tube 220 and is connected to the struts 224 to form an underfloor. A second cover sheet 226, omitted from Figure 14 for clarity, which may also be formed of rubberised fabric, is connected to the upper edge of the sidewall formed by portions of the second and third tubes 221, 222 and by the fourth tube 223. The area of the second cover sheet 226 is greater than the area enclosed by the tubes 220, 221 and the second cover sheet 226 is connected to the struts 224 (see Figure 18). The second cover sheet 226 is provided with two one-way inlet valves 227, 228.

An inflation system (not shown) is provided for inflating the tubes 2201, 221. 222, 223 and 224.

In use, the tubes 2201, 221, 222, 223 and 224 are deflated and packed, with the cover sheets 225, 226, in a container 229 (see Figure 15). The container 229 is deployed on water and the inflation system actuated, either manually or automatically. Gas is thus supplied to the tubes 220, 221, 222, 223 and 224 to inflate the tubes 220, 221, 222, 223 and 224. As a consequence, the chamber formed by the tubes 220, 221, 222, 223 and 224 and the cover sheets 225, 226 increases in volume. As a result, ambient air is drawn into the chamber through the inlet valves 227, 228 to fill the chamber with air. The cover sheets 225, 226 thus provide a cushioned floor for an occupant of the liferaft. This also provides the occupant with an insulating layer. The volume of gas required by the inflation system is reduced since no gas is required to inflate the floor. As seen in Figure 18, when the liferaft is fully inflated, the second cover sheet 226 is configured to provide an outer downwardly sloping portion and a central flat portion to receive an occupant.

It will be appreciated that there are a number of modifications that may be made to the embodiments described above with reference to Figures 12 to 18. The liferaft may have any conventional shape and be formed by any combination and shape of the inflatable tubes. The cover sheets need not cover the whole area of the liferaft; they could cover only part of the area. The inflatable tubes need not form a closed-shape they could, for example. form a U-shape in plan. It is not necessary to form a single chamber; two or more chambers might be formed. In addition, the principle described above with reference to Figures 12 to

18 could be applied to other inflatable structure such as barriers, jumping cushions, boats that are not Iiferafts, and aircraft escape slides.

Claims (22)

1. An inflatable structure comprising at least one inflatable member and at least one cover forming together an enclosed chamber, and inflation system for inflating the inflatable member, said inflation increasing the volume of the chamber and an inlet valve being provided for allowing air to pass into the chamber as the inflation member is inflated.

2. An inflatable structure according to claim 1 wherein the inlet valve is a one- way valve.

3. An inflatable structure according to claim I or claim 2 wherein the inlet valve is provided in the cover.

4. An inflatable structure according to any one of claims 1 to 3 wherein the inlet valve is one of a plurality of such valves.

5. An inflatable structure according to any one of claims I to 4 wherein the inflatable member forms a closed shape.

6. An inflatable structure according to claim 5 wherein the closed shape formed by the inflatable member has first and second generally parallel spaced surfaces, a first cover being connected to the first surface and extending over the closed shape defined by the inflatable member and the second cover being connected to the second surface and extending over the shape defined by the

inflatable member.

7. An inflatable structure according to claim 6 wherein the first cover and the second cover are interconnected such that the spacing of the first and second covers varies across the covers.

8. An inflatable structure according to any one of claims 5 to 7 wherein the inflatable member is formed by at least one inflatable tube.

9. An inflatable structure according to claim 8 wherein the inflatable member is formed by a plurality of inflatable tubes.

10. An inflatable structure according to claim 9 wherein the inflatable tubes are arranged side-by-side so that, when inflated, the tubes form a wall defining said closed shape, the formation of said wall on inflation increasing the separation of the first and second covers to increase the volume of the chamber.

11. An inflatable structure according to any one of claims 8 to 10 wherein the inflatable structure includes at least one inflatable bracing tube extending from a first location on the at least one inflatable tube across said closed shape to a second location on said at least onc inflatable tube.

12. A liferaft formed by an inflatable structure according to any one of claims I toll.

13. A liferaft according to claim 12 when dependent on claim 10 or claim 11 wherein, on inflation, the first and second covers form a floor of the liferaft with the inflatable tubes forming a sidewall of the liferaft.

14. A liferaft according to claim 13 wherein the first and second covers are interconnected so that, on inflation, the first cover forms an undersurface of the liferaft co-planar with the associated surface of the inflatable structure and the second cover is drawn by the interconnection towards the first cover to form with the sidewall a depressed central area for receipt of a person.

15. A liferaft according to any one of claims 12 to 14 and including a canopy that, when erected, provides shelter for an occupant of the liferaft.

16. An inflatable device comprising an inflatable support structures which, when deployed, supports a flexible outer envelope, the assembly of the support structure an the outer envelope being collapsible and the device further comprising a container within which the assembly is able to be stored in a collapsed state. the device further comprising a release arrangement for releasing the assembly from the container and the outer envelope having at least one port for inlet of ambient air, so that following release the outer envelope is expanded by the support structure, air being consequently drawn into the outer envelope.

17. An inflatable device according to claim 16 wherein an inflation system is provided for inflating the inflatable structure to expand the outer envelope.

18. An inflatable device according to claim 17 wherein the inflatable structure comprises at least one inflatable tube.

19. An inflatable device according to any one of claims 16 to 18 wherein the inflatable support structure and the flexible outer envelope form a liferaft.

20. An inflatable device according to claim 19 wherein the flexible outer envelope forms a floor of the liferaft.

21. An inflatable structure substantially as hereinbefore described with reference to the accompanying drawings.

22. A liferaft substantially as hereinbefore described with reference to the accompanying drawings.