the present invention comprises improvements in inflatable devices suitable for deployment inside or outside a boat or other marine vessel , for attachment to a vehicle or other object in water or to a vehicle or object that may enter a body of water as through breaking ice , or which may already be submerged . referring to the drawing , fig1 illustrates an inflatable bag 10 according to the invention comprising a sole layer of material , i . e ., a single wall construction of a woven , knitted , laid or deposited outer layer 12 of suitable weight covered on its inner surface 14 with a deposited layer of suitable thickness of thermoplastic material , including but not limited to films of polyurethane . the outer surface of the outer layer may also be coated with a deposited layer of thermoplastic film forming a protective cover for improved puncture and tear resistance . the outer layer 12 utilizes material such as rip - stop nylon , cordura , and ballistic fabrics with heavier weights being used as flotation lift bags in salvage operations , as well as for mounting on the exterior of vehicles travelling over frozen lakes . the weaves are in various weights ranging from 200 to over 1000 denier . the polyurethane covering for the inner surface 14 of the outer layer is applied either as a film liner or as a surface coating . the innermost coating is the most pliable and must be as impermeable to inflating gas as possible . the bag of fig1 includes an integral reinforced edge 16 of several heavy duty layers of material , sealed together to form a heavy tab 16a for bolting or otherwise fastening the inflatable to a boat , vehicle , etc . these tabs 16a are preferably used on additional sides of the inflatable bag , depending on application . in single wall bag construction of fig1 the edge seals are accomplished with one pass application of heat to form a sealed tab of 16a substantial width . alternatively , the tab seals may be accomplished in two passes applied to one side 16b then to the other side 16c of the tab to form a double seal . the double seal of the tab flanges is also accomplished in one pass using a &# 34 ; u &# 34 ; shaped application of heat simultaneously to both sides of the tab . for each sealing technique , there results a double sealed tab flange . if desired , the inflatable bag of fig1 may be enclosed within an outer protective cover 18 sewn , heat sealed , or fastened by cements or glues to the inflatable bag . the cover protects the inflatable bag from puncture and other damage without the ability to contain an inflating gas . in applying a protective cover , the outer surface of the inflatable bag is covered with a sufficient thickness of thermoplastic material such as polyurethane , pvc , and the like so that a heat sealing method will embed the protective cover in the outer surface of the inflatable bag . inflation of the bag 10 is achieved by means of valves 20a - c which typically include an inlet or inlet check valve , a pressure relief valve and a topping off valve . the flotation device 25 of fig2 comprises an inner buoyancy bag 26 and an outer buoyancy bag 28 . the peripheral flange or tabs 30 , 32 of inner and outer bags are heat sealed in a single bar seal , flat seal or double bar seal using heat sealing tools , high frequency ( ultrasonic ) heat sealing methods , as well as other sealing methods such as cements or glues . the &# 34 ; bag - within - a - bag &# 34 ; flotation device 25 provides an effective double walled flotation device employed individually or in combination with similar flotation devices to provide adequate lift for submerged objects , and also to maintain an object in a floating condition . the &# 34 ; bag - within - a - bag &# 34 ; is formed as follows . the inner bag 26 ( fig2 - 4 ) is dimensioned to fit tightly within the outer bag 28 . the upper 26a , 28a and lower walls of the inner ( not shown ) and outer 28b bags are individually assembled with a portion of the perimeter of their peripheral flanges 30 , 32 sealed leaving an opening through an unsealed portion 30a , 32a of the flanges of both inner and outer bags . next , the inner bag ( still having an opening through the unsealed portion of its peripheral flange ) is folded and inserted through the opening or unsealed portion of the flange of the outer bag . the inner bag is then unfolded or spread within the outer bag . aligned valve receiving openings 34 , 36 , 38 are then cut through the adjacent walls of the inner and outer bags for fitting bag inflating valves 40 , 42 , and 44 . the valve receiving components 46 shown in fig3 include a threaded receptacle 48 with inner flange 50 set into the opening 34 in the bag walls , an outer flange ring 52 and a tightening nut 54 for securing the assembly . if desired , rubber gaskets may be used between flanges and outer and inner bag walls . the threaded receptacle accepts an inlet check valve , or a pressure relief valve or a topping off valve . the valves are inserted with their flanges sealed to gas tightness against the bag wall . finally , the openings defined by the unsealed portions 30a , 32a of the flanges of the inner and outer bags are sealed to complete bag construction . the term &# 34 ; double wall &# 34 ; refers to the use of two separate layers of thermoplastic material to form inner and outer bag segments of a flotation device , either of which bags retains the inflation gas for an extra measure of safety and reliability in the inflatables thus constructed . in the &# 34 ; bag - within - a - bag &# 34 ; inflatable devices the bags are sealed completely with the lower half segment of the flange introduced inside the inner bag , and the outer half segment turned into place for final assembly . the &# 34 ; bag - within - a - bag &# 34 ; components of fig2 may be formed in other possible shapes including cylinders with closed end body panels , cubes with closed ends , triangular or trapezoidal cushion shapes or teardrop shaped inflatables to facilitate attachment to a submerged object . the inflatable bag 60 illustrated in fig5 comprises upper 60a and lower 60b walls sealed along a peripheral flange 60c defining an interior gas receiving interior . web straps 62 are fastened to the flanges of the inflated bag with a plurality , preferably three , straps 62a - c across and a longitudinal strap 62d . the straps provide a restraining mechanism to hold the inflatable in place in a boat vehicle , or an object to be lifted or floated in water . the attachment of the inflatable bag may be further strengthened by means of one or more stiff metal bars 64 to sandwich the strip tab , with the metal bars secured in place by heavy duty bolts 66 or a clamping mechanism . the inflatable bag 70 shown in fig6 is fitted with a restraining net 72 preferably woven of polypropylene fibers and rope , or woven or braided line , or of commercially available cargo net of sufficient strength . the net restraining mechanism gathers and fastens a margin 72a of the net along one or more edges 70a - d of the bag . a reinforced strip tab 74 may be used with the net fastened thereby using rigid metal bar stock 76 to sandwich the net and the reinforcing strip tab 74 , the resulting section being bolted or clamped at 76 in place to the object being floated . in another form of restraining web construction as an integral part of the inflatable bag , a network of woven webbing is constructed with webs encircling the bag , grommeted or otherwise fastened at sealed edges , and bolted at the bottom with heavy duty clamps through the webbing and reinforced bottom edge . the reinforced bottom edge includes several layers of high - denier material sandwiched and sealed integral with the inflatable bag itself . alternatively , the restraining net may merely encompass the inflatable bag without being fastened to the bag . in this case , the netting is provided with a ring or shackle for connection to a load to be floated . the inflatable is free then to assume the most natural shape imposed by hydrostatic pressure at unusual depths . as in the case of protective covers described above , the netting 72 may also be sealed into the outer walls 70e , 70f of the inflatable bag by coating the bag with a sufficient thickness of a thermoplastic material and heat sealing the web in the coated surface . a carryall soft valise 80 is shown in fig7 for containing an entire floatation system comprising several inflatable flotation bags 82 with a gas filled cannister 84 and a hose 86 connected from the cannister to each of the inflatables . typically , each hose may be up to four feet in length and folded in place when packed . from one to five inflatables can be folded and packed into a valise , each with a fill hose connected to the gas cannister . one soft valise comprises a portable system that when deployed may support a pleasure boat up to about 32 &# 39 ; in length . depending on the overall weight or displacement of the vessel or vehicle to be supported , a number of soft valises can be placed aboard . for use in an emergency , the valises are removed from their storage locations , the top zippers opened , the inflatables removed and flaked in the direction of desired deployment . a lanyard 88 is pulled , releasing gas from the storage cannister which remains in the bottom of the valise . all bags will inflate within a minutes time . an integral soft pouch enclosure 90 as shown in fig8 comprises an engineered or custom installation specified according to the lift required to float or hold up a vessel or vehicle if submerged . several pouches with inflatable bags 92 are distributed in the vessel for proper balance or trim and bolted at 94 into place along a securing tab 96 . preferably each inflatable bag 92 includes a reinforced securing tab along with restraining straps or net previously described in connection with fig5 and 6 . the inflatable bags 92 are folded and placed in the pouch so that the heavy reinforcing tab 96 and the tab of the pouch itself can be bolted as a unit to a structural member of the vessel or vehicle . in a typical installation the pouches are delivered ready for installation with a typical pouch measuring 24 &# 34 ; l × 9 &# 34 ; h × 4 &# 34 ; d . the pouch closure includes a hook and loop fastener 98 allowing the bag to burst forth from folded condition simply by activating the gas supply . the pouch is also fitted with a cutout in the rear panel for connection to the inlet check valve of the inflatable . the bag is folded in such manner and placed within the pouch so that the inlet valve registers with the pouch cutout . an advantage of a custom system is that the inflatables are attached low down in the vessel or vehicle so the vessel floats higher in the water after deployment of the system . in an alternate custom installation , each folded , inflatable bag is mounted in a durable , plastic pan fastened below the floor boards or bunk boards , thus hiding and protecting the inflatable bags . the bags are connected by suitable hoses to a gas supply . a modification of the engineered system permits extension of web straps 100 or use of netting so that when the system inflates , the bag , which may with its pouch , be enclosed in a small tray below a floorboard can inflate just above the side of the tray and not be constrained , even though having been folded down to a short length to fit into the tray . another modification allows a pouch to contain a gas cannister of sufficient capacity to inflate just one bag contained therein . in this modification , the gas cannister may have a simple turn valve 102 or a lanyard for deployment . the inlet valve featured in the inflatable devices of the invention is an inlet - check valve with inflation gas allowed to enter but not escape through the inlet after inflation . this feature is important in an emergency in case the fill hose becomes ruptured . the feature is also important if the hose is to be disconnected in switching to a back - up inflation system as in using a small gas compressor or electric air pump with fittings for connection to the inlet valve . another valve , the topping - off valve , is normally provided so that a manual pump can be connected from time to time to keep bags fully inflated . this is required in any inflatable system because no matter how well designed a system is , gradual weeping of air occurs . the pressure relief valve is necessary because the pressures in gas supply cannisters can vary significantly with temperature change . thus , in a flotation system deployed in the tropics , the gas may expand too rapidly and cause dangerous over inflation that must be rapidly relieved by the pressure relief valve . if a system is deployed in a polar region , under inflation can occur unless gas cannisters have a sufficient gas supply . accordingly , inflation systems are designed with sufficient gas for complete inflation at low ambient temperature , and with a pressure relief valve to exhaust excessive gas pressure at high ambient temperature . in the case of inflation devices designed for lifting submerged objects , where an object is to be lifted from deep water , the pressure in the lift bag can increase so rapidly that it will burst the bag unless the pressure is relieved . in this regard , an alternative means for accommodating over - pressure is an oversize bag so that gas volume at differing ambient temperatures provides sufficient lift for a salvage application without ever reaching the burst pressure of the bag . a suitable method for lifting submerged objects is to construct an inflatable bag with an open bottom , attaching the submerged load to a lift ring at the bottom of a harness holding the open bottom down , and within the open bottom allowing excess inflation gas to escape rapidly as the bag ascends bearing the submerged load . fig2 illustrates valves 40 , 42 , 44 which are typically inlet or inlet check , pressure relief , and topping off valves . the inlet or inlet check valve opening may have either male or female threads of various standard sizes for use with pressure hoses and gasses , including for use with standard automobile or truck tire valves in fig1 alternative locations of inlet or inlet check , pressure relief , and topping - off valves 20a - c are shown . fig5 illustrates another preferred location of inlet or inlet check , pressure relief , and topping - off valves 61 , 63 , 65 . in flotation devices for some applications additional pressure relief valves are mounted to provide sufficient dump capacity when inflating at a higher ambient temperature or in order to provide such capacity for faster return from below to the surface of the water . some applications , as for example , when hand turn valves are used for inflation , may not require pressure relief , as long as the turn valve is monitored and shut off when the bag is inflated to design pressure . similarly , topping - off or pressure relief valves may not be needed if the inlet valve is connected to a gas supply using a controllable compressor , as in a diving application , or in a truck air brake system or using the air from a large truck tire in the case of containment of leaks from a chemical delivery truck . each inflatable , after being bolted in place , is connected by hose to a gas cannister with a supply of gas for inflation . with a lanyard from the gas cannister led to a convenient location , the system is ready for deployment at a moments notice . ordinarily , there is sufficient time for deployment before a vessel or vehicle sinks . once the lanyard is pulled the entire system inflates in a minute or so . fig9 shows a typical gas cannister 110 together with its inflation valve 112 . the inflation valve features a lanyard pull 114 which activates the valve so that gas is released to a manifold 115 , to which is connected individual gas hoses 116 leading to the inflatable bags forming the flotation system . the gas cannister is sized to provide capacity to fill the number of inflatables in the system . the cannister design also is appropriate for the gas to be used , usually carbon dioxide , a combination of co 2 and nitrogen , or air . a sufficient quantity of co 2 normally requires only about half the volume as for air . nonetheless , air may be more convenient if the user is a diver with scuba tanks , as for example where the inflatables are used for salvage . in addition , air may be specified as a back - up supply in some applications , in which case additional fittings must be arranged for both co 2 and air . when co 2 is used , some nitrogen can be added to extend the temperature range over which the gas will be of sufficient volume . also , nitrogen is introduced at higher pressures which allows filling the inflatables more rapidly . the inflation valve is normally provided with a fill stud 18 and separate pressure relief valve 120 . the fill stud allows various methods to be used for filling the cannister with gas . the pressure relief valve provides a measure of safety in case of overfilling by pump or in case the cannister is exposed to too high an ambient temperature . in one modification of the gas cannister and inflation valve , separate adapter fittings 122 are made to allow connection to a wider range of commercially available cannisters , or to allow the adapting of commercially available filled - and - sealed cannisters to different types of inflation valve actuators . if desired , a pyrotechnic inflator or hybrid combination of a pyrotechnic inflator and gas cannister may be used for inflation . the gas cannisters can be mounted in out - of - the - way places with a lanyard extending to reach the most convenient location for emergency deployment in vessel or vehicle . similarly , in an engineered system the hoses are made of sufficient length to reach all the installed inflatable bags . in some instances it may be found convenient to use &# 34 ; y &# 34 ; connectors at some distance from the gas cannister . in these instances , it is necessary to provide balance of back pressures in the system , using different diameters of hose . inflation valves are normally fitted with a safety pin used to prevent inadvertent release with the safety pin removed before deployment . in use , a quick pull on a lanyard of about 15 pounds will release gas to inflate a complete system in less than a minute where co 2 is used and a fraction of a minute where high pressure air is used . if manual or electric air pumps are used inflation time will be substantially increased - to several minutes per bag . the inflation system can be actuated by automatic means such as solid state or mechanical float switches with a small dedicated battery or house battery . the float switches actuate a pyrotechnic squib which expands in a small chamber to open the inflation valve . in a similar manner , a panic button can be rigged using a push button switch and the pyrotechnic charge described . in every case of automatic actuation , there is a back - up manual lanyard in case of failure of any aspect of the automatic system . in certain applications such as lift bags for salvage , it is necessary and desirable to keep debris , ropes , and cables from impinging directly of the inflatable bags . as an example , when a bag comes to the surface in the course of lifting a heavy object and must be towed for some distance before discharging the load , it is desirable to keep debris and seaweed from becoming entangled with the harness or bag . for this purpose , an external and integral shroud 130 ( fig1 ) may be furnished as a part of bag design . the shroud is constructed of smooth , woven elastic material , cut and sealed or sewn , to fit tightly about the inflatable and its harness . the shroud includes upper and lower 134 towing shackles . for vehicles such as tracked vans travelling over a frozen lake , the inflatable systems of the invention are mounted to the lower side panels outside the vehicle so as not to consume interior space . heavier weights of material such as ballistic cloth are used of sufficient strength to withstand crashing through ice . the types of vehicles travelling on ice includes all - terrain vehicles , larger tracked vans , and tracked grooming vehicles used on snowmobile trails which sometimes traverse nearby rivers and lakes . the bags according to the invention are also used for spill containment of oil and chemicals . this application uses low weight and light bulk inflatables in a range of sizes , as for example an inflated round or rectangular tube supporting a central apron in which the spill is collected . it is to be understood that flotation devices according to the invention are suitable for a variety of applications including deployment in marine vessels , lift bags for marine salvage , in all types of vehicles such as track vehicles , vans , snowmobiles , as well as for chemical and oil spill containment on land and on bodies of water . various changes may be made to the structure embodying the principles of the invention . the foregoing embodiments are set forth in an illustrative and not in a limiting sense . the scope of the invention is defined by the claims appended hereto .