Abstract:
A self-righting inflatable life raft ( 10 ) comprises a raft body ( 11 ) having inflatable side walls ( 21, 22 ) and a floor ( 15 ) located therebetween. At least two inflatable tube members form arches ( 51, 52 ) that extend from one side of the raft body to the other, each arch extends upwardly and outwardly from a perimeter of said raft body ( 11 ) at an angle from the perpendicular to said raft body. The life raft has a central axis of symmetry ( 61 ) and a center of gravity through which the weight of the life raft acts to rotate the raft on the surface of water from an unstable inverted position to a stable upright position. The tube members when inflated have a buoyancy sufficient to exert a turning moment on the life raft ( 10 ) causing the life raft to topple by gravity to an upright position. At least one inflatable interconnecting tube ( 70, 71, 72, 76, 77 ) is positioned between the arches ( 51, 52 ) and offset from the central axis ( 61 ) to increase the turning moment.

Description:
TECHNICAL FIELD 
     This invention relates to an inflatable life raft having inflatable tubes dimensioned and positioned to cause the life raft to turn upright in the water without assistance if the raft inflates in an inverted position or to return an inflated raft to an upright position if it is subsequently overturned. 
     BACKGROUND ART 
     In U.S. Pat. No. 4,998,900, there is described and illustrated a self-righting inflatable life raft having upwardly and outwardly extending inflatable tubes. These tubes are arranged to cause the life raft to be unstable if inverted. In particular, the centre of gravity of an inverted life raft will fall outside the supporting area, that is the top of the inflatable tubes, so that the life raft will topple under gravity back to an upright position. 
     If the inflatable tubes in these prior constructions do not inflate or, after inflation are subsequently collapsed or distorted, they may not adopt their desired positions extending upwardly and outwardly from the side of the walls of the main body, sufficient to make the life raft topple to the upright position. 
     In patent application PCT/AU96/00409 similar self-righting inflatable life rafts were disclosed incorporating ties in the form of flexible ropes, wires or inflatable tubes fixed between two spaced points on the life raft to limit separation of the two points to the length of the tie during and after inflation of the tube members. The two points were chosen to inhibit distortion or collapse of the tube members from their desired positions when inflated. 
     SUMMARY OF INVENTION 
     It is an object of the present invention to provide a life raft which can reliably return to an upright position if inverted. 
     According to the present invention there is provided a self-righting inflatable life raft comprising a raft body having inflatable side walls and a floor located therebetween; and at least two inflatable tube members forming arches that extend from one side of the raft body to the other, each arch extending upwardly and outwardly from a perimeter of said raft body at an angle from the perpendicular to said raft body; said life raft having a central axis and a centre of gravity through which the weight of the life raft acts to rotate the raft on the surface of water from an unstable inverted position to a stable upright position, wherein the tube members have a buoyancy sufficient to exert a turning moment on said life raft causing said life raft to topple by gravity to an upright position, characterised in that at least one inflatable interconnecting tube is positioned between the arches and offset from a central axis to increase the turning moment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described by way of reference only with reference to the accompanying drawings in which: 
     FIG. 1 is a perspective view of first embodiment of a self-righting life raft of the present invention; 
     FIG. 2 is a similar view of the life raft in FIG. 1 but with the canopy removed; 
     FIG. 3 is a plan view of the life raft in FIG. 2; 
     FIG. 4 is a side view of the life raft in FIG. 2; 
     FIG. 5 is an end view of the life raft in FIG. 2; 
     FIG. 6 is a view of the underside of the life raft in FIG. 2; 
     FIG. 7 is a plan view of a second embodiment of a self-righting life raft of the present invention; 
     FIG. 8 is a side view of the life raft in FIG. 7; 
     FIG. 9 is an end view of the life raft in FIG. 7; 
     FIG. 10 is a plan view of a lower panel of the base structure of the second embodiment of the life raft; 
     FIG. 11 is a plan view of an upper panel of the base structure of the second embodiment of the life raft; 
     FIG. 12 is a plan view of a square life raft in accordance with the present invention; 
     FIG. 13 is a plan view of a hexagonal life raft in accordance with the present invention; and 
     FIG. 14 is a plan view of a circular life raft in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 to  6  are views of a first embodiment of a self-righting life raft that is designed to hold six people. FIGS. 7 to  10  illustrate a second embodiment of a life raft which is designed to hold twenty-five people. FIGS. 11 to  13  illustrate life rafts having base structures of different shapes. It is understood that the life raft may be scaled up or down in size to accommodate varying numbers of persons. For example, the size of the first embodiment can be altered to accommodate six, fifteen or twenty-five persons. 
     The life raft is constructed of inflatable tube sections and all Figures show various embodiments of life rafts in fully inflated operational configurations. It is however understood that the life raft is designed to be stored in a collapsed configuration where the tubes are deflated and the whole raft can be folded into a suitable container. To use the life raft, the life raft is dropped into the water and then on appropriate signal one or more gas cylinders that are housed within the life raft structure open to inflate the tube sections to cause the life raft to progressively assume an inflated configuration. 
     The self-righting life raft  10  illustrated in the accompanying drawings is constructed of inflatable tube sections that are coupled together to define a life raft comprising a base structure  11  and a superstructure  12  formed by an arrangement of arches. The geometry and arrangement of the inflatable tubes is such that the life raft always assumes an upright configuration with the superstructure  12  being above the water level. 
     The superstructure  12  supports a canopy  13  (shown in FIG. 1) that extends above the base structure  11  which has a floor  15 . The floor has two central drainage holes  17  for draining water if the base structure fills with water. It is understood that the present embodiments of the self righting life raft contain standard features common to most life rafts including stabilising pockets which fill up with water to act as ballast, a drogue, lights, deflate screws, etc. Such standard features have been omitted from the drawings in the interest of clarity. 
     As shown in FIGS. 1 to  6 , the base structure  11  and superstructure  12  of the first embodiment are constructed from linear cylindrical tube sections that are joined together in an angular array to define the structure as shown in the drawings. The base structure  11  comprises two superimposed arrays of tube sections defining a lower base panel  21  and an upper base panel  22  (see FIGS. 10 and 11 for views of upper and lower base panels of the second embodiment) and a further array of tube sections defining a sub-panel  25  located under lower panel  21 . Each base panel  21  or  22  comprises twelve segments that include two side panels  23 , two end panels  40  and interconnected panels  41  between the side and end panels so that the base is somewhat in the form of an oblong with longer sides and shorter ends. One shorter end supports an entry platform  30  comprising a tubular cross member  33  that is attached parallel to shorter side panel  40 . The other end supports a rope ladder  26  which hangs on the outside of the base structure  11 . The upper base panel  22  is substantially the same as the lower base panel  21  and is superimposed vertically with the floor  15  attached to the base of the lower panel. Sub-panel  25  is shown in greater detail in FIG.  6 . Sub-panel  25  comprises a circular array of six inflatable tubes forming a hexagon with one pair of opposing tubes being aligned parallel with side panels  23  of base panel  21 . Slightly recessed from the perimeter of base panel  21 , sub-panel  25  extends across the width and length of the base structure and provides spacing between floor  15  and cold water beneath the life raft so as to insulate the floor from the cold water. 
     The superstructure  12  is illustrated in FIGS. 2 to  5  and comprises two transverse arches  51 ,  52  extending transversely across the life raft  10 . Transverse arches  51 ,  52  comprise a pair of outwardly inclined outboard struts  60  joined to a pair of inwardly inclined intermediate struts  62  that are in turn joined to a pair of further inwardly inclined roof struts  63 . Roof struts  63  meet at an apex  64  at the central longitudinal axis  61  (FIG. 3) of the life raft  10 . Transverse arches  51 ,  52  are positioned in a parallel spaced apart manner extending across the side panels  23  of the base structure  11 . 
     Transverse arches  51 ,  52  are interconnected by an upper interconnecting tube  76  and a lower interconnecting tube  77 . Both interconnecting tubes  76 ,  77  are asymmetrically arranged of the arches to improve the self-righting characteristics of the raft. Both interconnecting tubes are also offset from the central axis  61 . Upper interconnecting tube  76  interconnects the arches  51 ,  52  on one side of the central axis between corresponding roof struts  63 . Upper tube  76  is positioned on roof struts  63  closer to the apex  64  of the arches than the joint  65  between roof strut  63  and intermediate strut  62 . Lower interconnecting tube  77  is located between the arches on the other side of the central axis to upper interconnecting tube  76 . Specifically, lower interconnecting tube  77  is located at the joint  74  of outboard strut  60  and intermediate strut  62 . Lower interconnecting tube  77  also has rounded end portions  73  protruding from the other side of joint  74  to the main portion of lower tube  77 . The lower interconnecting tube  71  is larger in diameter than upper interconnecting tube  76 . 
     The combination of inflatable interconnecting tubes  76 ,  77  and the outward inclination of the arches provides the raft with a righting ability wherein stability and buoyancy in righting moments enable the life raft to self right if inflated inverted. 
     The base structure  11  is further provided with thwarts  75 , that is, linear inflatable tubes provided transversely above the floor  15 . Specifically, two thwarts are provided above floor  15  between side panels  23  and generally vertically aligned with transverse arches  51 ,  52 . The thwarts provide structural rigidity to the life raft  10  and ensure the base structure  11  is flat when inflated such that, when inverted, the weight of the life raft, particularly the base structure, acts through the centre of gravity of the raft causing it to rotate into an upright position. Additionally, the thwarts ensure that the base structure does not fold under the weight of occupants when the raft is inflated. Thwarts  75  can double as seats for occupants. 
     When inverted the buoyant superstructure causes the line of force of the centre of gravity to fall outside the area supporting the raft thus causing the raft to become unstable and rotate into an upright position where the raft reaches a state of equilibrium. 
     As shown in FIG. 1 the canopy-type cover  13  is suspended above the base structure  11  and over the superstructure to protect the occupants from wind, rain and sun exposure. Additionally, the canopy has the effect of limiting movement between the arches and base structure and between the arches themselves which encourages the superstructure to achieve the desired configuration upon inflation. Generally, the canopy  13  is attached at its perimeter to the sidewalls defined by the base structure  11  and suspended centrally from the transverse arches  51 ,  52 . The canopy in the first embodiment has two entrance openings, one at each end and corresponding with platform  30  and ladder  26 . The canopy is typically made from a lightweight fabric which repels rain and wind but allows breatheability of the enclosed area of the raft  10 . 
     As mentioned above, the arches, the beams, the base structure and thwarts are formed by cylindrical tubes that are interconnected to define two closed pneumatic circuits that are inflated by means of two gas cylinders (not shown) that are supported beneath the base structure and open at a predetermined signal. The gas cylinders carry more than enough gas to inflate the life raft structure to the desired pressure. A first cylinder inflates the lower half of the base structure  11  including thwarts whilst the second cylinder inflates the top half of the base structure  11  and the superstructure  12 . Each circuit is provided with pressure relief valves  44  that allow excess gas pressure to be released thereby ensuring that the circuits are inflated to the desired pressures. The length of the tube sections vary depending on where they are positioned in the structure and the diameters of tube sections vary between approximately 250 mm to 400 mm depending once again on their position. For example, lower base panel  21  in the first embodiment is 380 mm in diameter whereas upper base panel  22  has a diameter of 310 mm. Likewise, lower interconnecting tube  77  has a larger diameter at 400 mm compared with upper interconnecting tube  76  which has a diameter of 270 mm. Diameter dimensions of the inflatable tubes may not be readily discernible from the drawings. 
     The self-righting characteristics of the raft are defined by the buoyancy forces that are placed on the raft structure should it be inflated whilst inverted in the water. The design of the superstructure with the outwardly angled outboard struts and the asymmetric location of the interconnecting beams has the effect of imparting an upward buoyancy force that causes the structure to turn about an axis and rotate to a righting position. The diameters of the tubes and the inflation pressures have been carefully selected to ensure there is an adequate force to impart the desired rotation. It has been discovered that tubes inflated to 3.5 psi for the upper base panel  22  and superstructure  12  and 2.5 psi for the lower base panel  21  and thwarts  75  provides the adequate buoyancy force. The pressure relief valves ensure that the tube sections are inflated to the desired pressure and it is important to note that the life raft must operate satisfactory between extreme temperatures of −30° C. and +65° C. 
     A second embodiment of the life raft  10  is illustrated with particular reference to FIGS. 7 to  11  and comprises the two transverse arches  51 ,  52  described in the first embodiment with the addition of a longitudinal arch  50 . The longitudinal arch  51  extends along the central longitudinal axis  61  of the life raft and comprises a pair of inclined uprights  53 ,  54  joined by a horizontally extending cross member  55 . Each transverse arch  51  or  52  extends transversely across the life raft  10  as in the first embodiment but comprises a pair of outwardly inclined outboard struts  60  joined directly to a pair of inwardly inclined roof struts  63  that meet at the apex  64  along the central longitudinal axis  61  of the life raft  10 . The roof struts  63  of the arches extend over the top of, and are secured to, the cross member  55  of the longitudinal arch  50 . The transverse arches  51 ,  52  in this embodiment are interconnected by three interconnecting tube members  70 ,  71 ,  72 . 
     FIGS. 10 and 11 show the lower base panel  57  and upper base panel  58  which superimpose to define the base structure. In this embodiment the base structure comprises twelve panel segments that include two longer side panels  23  and ten interconnected shorter panels  41 . There is only one entry platform  30  situated at one of the longer side panel  23  and it comprises a tubular cross member  33  attached parallel to side panel  23  and a pair of parallel tubular arms  31 ,  32  extending from tubular cross member  33 . Accordingly, the canopy in this embodiment (not shown) has only one entrance opening at side  23  of raft corresponding with entry platform  30 . 
     The three interconnecting tubes  70 ,  71 ,  72  are specifically positioned asymmetrically of the raft  10  to improve the self-righting characteristics of the raft. The interconnecting tubes are designed to be of 300 mm cylindrical tube sections. The two tubes  71 ,  72  extend between the arches in the same plane as that part of the arches. The tube  72  is located just inside the join of the outboard strut  60  and roof strut  63  on one side of the raft. The tube  71  is positioned just to the other side of the central axis  61 , or other side of the cross member  55 , near the apex  64  of the transverse arches  51 ,  52 . The third tube  70  is positioned to extend across the top of the transverse arches  51 ,  52  at a position near the apex of the tubes but below the central axis as shown in FIG.  7 . Two ( 70 ,  71 ) of the three tubes  70 ,  71 ,  72  are positioned on one side of the raft  10  axis  61 . This is also the side that facilitates passenger entry via the entry platform  30 . The location of two  70 ,  72  of the tubes to the one side and the third tube  71  on the other side near the central axis prevents kinking of the arches on inflation and further enhances the upwardly rotational force that causes self-righting of the raft  10 . 
     It is important that the tubes and arches that make up the self righting superstructure assume the desired configuration on inflation. Thus, kinking or entanglement of the tubes and arches must be avoided and stability and buoyancy improved. The interconnecting tube members overcome the problem of kinking and entanglement. However as a further feature the second embodiment also includes ties  80 ,  81  positioned between the base structure and the arch tubes to limit the amount of movement that the arches can move away from the base structure. The position of the ties  80 ,  81  is shown in detail in FIGS. 8 and 9. Essentially the ties  80 ,  81  simply comprise a length of 8 to 10 mm rope that is attached at either end to include patches that are glued onto the structure of the life raft. As shown in FIGS. 8 and 9 two ties  80 ,  81  are positioned on the same side of the raft, that is the entry side. One tie  80  is coupled to the right hand transverse arch  52  of FIG. 8 on the center line of the roof strut  63  at a position inside but close to the join between the outboard strut  60  and roof strut  63 . The other end of the tie  80  is attached to the edge of one shorter panel  41  of the lower base panel  57 . The other tie  81  is attached to the left hand transverse arch  51  of FIG. 8 in a symmetrical manner as the tie  80 . 
     Life rafts of a third embodiment are illustrated in plan view in FIGS. 12 to  14 . The rafts have base structures of different cross section so that FIG. 12 illustrates a square base  180 , FIG. 13 a hexagonal base  90  and FIG. 14 a circular base  184 . These life rafts are smaller than the life raft of the first and second embodiments. The life raft is constructed of the same type of cylindrical tube members as described with reference to the first and second embodiments. However, the superstructures  111  of these rafts are different from previous embodiments in that they comprise two inflatable arches  182 ,  188  positioned mutually perpendicular to each other rather than parallel. The crossing point of the arches forms the central apex  140  of the superstructure. The arches of the superstructure  111  are in the form of inflatable tube sections  122 ,  124 ,  126  and  128  that extend upwardly and outwardly of the base structure to converge towards the apex  140  of the structure. The arches as shown in FIGS. 12 to  14  each comprise outwardly inclined uprights and join with roof struts that meet at the central apex  140 . In these life rafts, the central axis about which the raft undergoes a turning moment extends across the raft along either one of the two arches  182 ,  188 . 
     In all the embodiments shown in FIGS. 12 to  14  a single bridging beam in the form of an inflatable tube  150  is positioned on top of the arches extending between two adjacent arch tube members in one corner of the raft as shown. The bridging tube  150  is positioned on top of the arch tube members and is a cylindrical tube that is longer than the space between the arch members so that the tube as shown in the drawings overlaps at its ends  151 ,  152 . The tube  150  is specifically positioned near the corner of the raft that is adjacent the opening in the canopy. Tube  150  is positioned upward and outward of the arch members to increase the buoyancy effect that the tube has on the life raft should it be inflated in an inverted position. The fact that it is also offset from the central axis of the raft causes a turning moment which encourages the raft to self right. 
     In a fourth embodiment, the arches of the oblong-shaped raft in the first and second embodiments, are interconnected by one, two or three symmetrically positioned interconnecting tube members extending laterally on either side of the central axis between the arches in a spaced parallel configuration. In other words, one, two or three pairs of interconnecting tubes are arranged between the arches symmetrically of the central axis and the longitudinal arch (if one is provided). The interconnecting tubes are of the same diameter as the other arch tube members and are inflatable in the same manner. In a situation where a life raft has more than two arches it is understood that all the arches will be interconnected by the interconnecting tube members. Inextensible straps, ropes or ties between the arches further increases the self righting characteristics of the life raft by restricting the orientation of the tube members when deflated and ensuring that as the tube members inflate they assume the geometry that ensures that the raft rotates to the correct floating position. 
     It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention.