INFLATABLE HULL STRUCTURES AND DEMOUNTABLE JOINT BETWEEN ELONGATED STRUCTURAL ELEMENTS

Abstract: A demountable catamaran has a pair of inflatable hull structures each comprising an inflatable hull tube (4) and an extruded generally rectangular aluminium tubular beam (5) having at its lower surface two inclined support surfaces on oppposite sides of a channel having a narrow entry. The hull tube (4) has an upstanding web extending through the entry to carry an enlarged bead (15) within the channel to lock the inflatable tube to the hull beam (5). The hull beams (5) are secured by demountable joints to cross beams (2) and (3). The stem of each hull carries a rudder assembly which can yield when the rudder hits an underwater obstruction.

Description: INFLATABLE HULL STRUCTURES AND DEMOUNTABLE JOINT BETWEEN ELONGATED STRUCTURAL ELEMENTS The present invention relates to demountable joints between elongated structural elements which are to be secured to each other at an angle, typically 90°. The invention also relates to inflatable hull structures for boats. Two or more such hull structures may be detachibly secured to cross beams by the demountable joints to form a multi-hull boat such as a catamaran. The present invention also relates to rudders and is particularly suitable in respect of sailing boats such as dinghies and catamarans. The invention which is defined in the claims, will now be further described by way of example with reference to the accompanying drawings, in which:- Fig. 1 is a perspective view of a catamaran embodying the invention; Fig. 2 shows a bow of the catamaran partly in elevation and partly in longitudinal section, on an enlarged scale; Fig. 3 is a vertical cross-section on the line IXI-III cf Fig. 2; Fig. 4 is a cross-section on the line IV-IV of Fig. 2 on a further enlarged scale; Fig, 5 is a cross-section on the line V-V of Fig. 1; Figs. 6 and 7 are plan and side elevationsl views of the aft end of one of the inflatable hulls; 1?ig. 8 is an elevational view- of a portion of the side of the framework of the catamaran shoving the connection of a cross beam to a hull beam; Fig. 9 is a plan view of the connection shown in Fig. 8; " ' Fig. 10 shows a vertical cross section on the line X-X of Fig. 9; Fig. 11 shows the portion within the circle XI of Fig. 9 on an enlarged scale; Figs. 12 and 13 show the first and second brackets in flattened form, prior to bending; Fig. 14 is a side elevational view of the stern of one hull showing the components of the rudder; Fig. 15 is a plan view of the rudder shown in Fig. 14; Fig. 16 is a view on an enlarged scale of the connection between the connecting rod and tiller shown in Fig. 14 in the direction of the arrow XVI, and Fig. 17 is a plane view of the stern of the catamaran showing the linkage between the two tillers. The demountable catamaran shown in the drawings comprises a pair of hull structures 1 interconnected by detachable cross-beams 2 and 3. Each hull structure 1 comprises an inflatable hull 4 in the form of a tube of cross-section which varies along its length to give the required form to the hull, a hull beam 5 extending along the top of the hull, a bow member 6 interconnecting the tapered down bow of the hull tube 4 with the hull beam 5, and a stern post 7 carrying a rudder assembly 8, the rudder assemblies being linked by a tiller link tube 9. As is shown clearly in Figs. 3 and 5, each hull beam 5 is of generally rectangular tubular construction, being formed from a length of aluminium alloy extrusion, suitable alloys being those used for yacht masts such as international designation 6082 in condition TF. The bottom wall of the hull beam 5, however, consists of two support surfaces or flanks 11 which slope upwards at about 30° to the horizontal from near the bottom edges of side walls 12 of the hull beams to an entry portion 13 leading into a channel 14 OMPI which is conveniently shaped as the major portion of the circle. Where the entry portion 13 meets the channel 14, the width of the entry portion is further reduced by a nose formation on each side of the entry to the channel 14 thereby further reducing the width of the resulting throat and providing an increased - . thickness of metal at the bottom two edges of the channel 14. The hull beam extrusion is completed by a top wall 15 which is joined to the top edges of the side walls 12 by arcuate portions 16. The extrusion may for example have a wall thickness of 2mm, a height of 85mm and width of 80mm. Each hull tube 4 is constructed of suitable flexible air tight and water tight material, such as • woven nylon cloth coated with polyurethane. Along its top edge, each hull beam has an upstanding rib consisting of a web portion 14' and a bead 15'. The height of the web portion 14' and diameter of the bead portion 15 of the rib are such that with the hull 4 deflated or only partially inflated, one end of the bead 15 can be introduced into an end of the channel 11 and then slid along the channel to the other end, thus drawing the remainder of the bead 15 into the channel 11. ' Since the bead 15' is clearly much thicker than the throat of the entry portion 10 to the channel 15, it cannot be pulled downwards out of the channel through the entry portion. Thus, when the hull 4 is fully inflated, it will expand into bearing contact with the wall portions 8 and apply tension to the web 14' . As a result, the hull tube 4 is now firmly anchored to the hull beam 5 effectively uniformly along its full length. Conveniently, the web 14". and bead 15' can be formed by a 96mm wide strip of woven nylon cloth folded around a bolt rope or cord (to form the bead 15'), with O PI adjacent portions secured together to form the web, the marginal portions being fixed to the inflatable hull by an appropriate (impact) adhesive and formi g the bearing areas to contact the surfaces 11. The inner 5 face of this strip is coated with polyurethane but the outer surface is preferably left uncoated to assist sliding in the channel 13, 14 prior to full inflation of the hull. As shown in Fig. 1, each of the cross beams 2 and 10 3, can be formed from a length of substantially circular extrusion of the same material as the hull beams 5. Each cross beam 2, 3 is detachably secured above the top of each hull beam by a set of brackets 18 - and stainless steel bolts as described below with 15 reference to Figs. 8 to 13. As explained above, the hull 4 when fully inflated is firmly anchored to the hull beam 5 which is in .contact with the hull 4 over a large area and over substantially the whole length of the hull except the 20 foremost part thereof, so that substantial loads can be applied to the hull without creating large local pressures which would deform the hull. At the same time, during assembly, the structure can accommodate minor dimensional changes in the hull which may for 25 example occur during early use or aging of " the hull. As can be seen in Fiqs. 6 and 7, the height of the web portion of the anchoring rib of the hull tube preferably increases over the aftermost end of the rib, for example for a distance of about 100mm. This 30 performs a stress-relieving operation on the aft end of the rib to prevent tearing of the end of the rib under the highly concentrated forces which would otherwise be exerted on it by the high lateral forces exerted on the hull tube for example when the helm is suddenly put ' 35 hard over. In order to form a bluff stern to the hull tube 4, OMPI the aft end of it is bonded to the periphery of a dished circular rigid plate 21 which carries an inflation valve 22. The stern post 7 also carries conventional pintle brackets for mounting the rudder assembly 8. The circular plate 21 should be spaced from, the stern post 7 to prevent chafing. At its bow end, the hull tube 4 tapers down to be bonded to a smaller diameter dished bow plate 23, (Figs. 2, 3 & 5) and in this region is spaced from the hull beam 5. In accordance with British Patent Specification No. 2024112 (US 4,284,024) the bow member 6 forms a pair of bow cheeks 24 meeting at a sharp bow stem 25. The bow member 6 is hollow and formed by a rotational moulding method from polypropylene. In its upper aft face is formed a socket 26 to receive and engage the forward end of the hull beam 5, the bow member being mounted on the hull beam after the hull tube 4 has been assembled to the hull beam. The forward dished plate 23 has a central depression 27 which snugly engages on a circular boss 28 on the bow member 6. The boss 28 is surrounded by a shallow annular depression receiving the outer portion of the dished plate 23. This arrangement ensures positive location of the forward end of the hull 4 in all radial directions. To hold the plate 23 and boss 28 in contact, a loop of cord 29 secured to the hull 4 passes through the eye 30 of a nylon slider 31 which can be slid into a short vertical track 32 glued and screwed (at 33) to the bow member 6. Once the slider 31 has been engaged in the track 32, the bow member can be engaged on the hull beam, the hull tube can be finally adjusted • relative to the hull beam and then inflated. To close the gap between the hull beam and the OMPI forward tapering portion of the hull 4; a furthe rpiece of nylon cloth 35 is folded at its middle over the bolt rope B, forming a forward extension of the bead 15 and bonded at its lower margins to the tapering hull 4. To complete the boat as a sailing boat, a mast 36 (with sail 36a) can be mounted in the centre of the front cross beam 2 at 40 and stayed by stays such as 38 to suitable points 37 on the hull beams 5. A trampoline deck (not shown in Fig. 1) extends over the area between the cross beams 2 and 3 and the hull beams 5. Also, dagger boards, of profile similar to the rudders, may be mounted in frames (not shown) fixed to the inboard side of each hull beam, between the cross. members. Since there is only a single rib 14, the rib does not have to be positioned with extreme accuracy since the flexible hull can accommodate minor inaccuracies with causing major stresses or wrinkles. In Figs. 8 to 13 is shown a demountable joint between a hull beam 5 and an end of a tubular cross beam 2 or 3. A pair of first brackets 55A and 55B is secured to the flat side face 53 of the hull beam 5. A pair of second brackets 56A and 56B is similarly secured to the opposite face 54 of the hull- eam 5. The brackets 55 are formed from metal sheet or pla e having the outline shown in Fig. 12 while the brackets 6 are similarly formed from plate or sheet metal having the outline shown in Fig. 13. Thus, each bracket 55 has a mounting portion 57 which is bonded to the face 53 and further secured by rivets 58 which pass through holes- 59 in the mounting portions 57 and corresponding holes drilled in the face 53. Each bracket 55 also has a bridge portion 61 connected to the mounting portion 57 by a bend zone 60 which forms a quarter of a cylinder as the result of the bending operation to OMPI place the bridge portion 61 at right angles to the mounting portion 57. This bending operation takes place in opposite directiosn for the opposite-handed brackets 55A and 55B. Each bridge portion 61 has an upper flange 62 which is bent through an angle of 30° to the remainder of the bridge portion 61 about a bend line 63. The flange 62 is formed with two spaced holes 64 and 65. The second bracket 56 also comrpises a generally triangular mounting portion 66 and a flange portion 67 which is connected to the mounting portion 66 by a bend zone 68, the plate 56 being bent in the zone 68 to brign the flange 67 at right angles to the mounting portion 66. This bending takes place in opposite directions for the opposite-handed second brackets 56A and 56B. The flange 67 has a hole 69 of the same diameter as the hole 65 while the mounting portion 66 is formed with a pattern of four rivet holes 70 to enable the mounting portion to be bonded and rivetted to the face 54. The preferred method of assembly of the connection is as follows. The cross beam 2 (or 3), which is of generally circular cross section but is formed with two diametrically opposed flat surfaces 73, has two pairs of diametrically opposed holes drilled through the flat όurfaces. The spacing of the holes in each flat surface corresponds to the spacing of the holes formed in the brackets 55. The pair of opposed holes nearer to the end of the cross beam is spaced from .that end by a distance corresponding to the distance between the holes 64 and the mounting portions 57 of a bracket 55. Thus, a bracket 55 may conveniently be used as a template when marking off the correct positions for the holes to be drilled. The holes 65, 69 of respective brackets 55, 56 are held in alignment while a stainless steel bush 71 having a flange at one end is passed by its other end through the aligned holes and thereafter swaged to secure the portions 62 and 67 of the respective brackets permanently but pivotally together. Similar bush can be inserted and secured in the hole 64 to act as a protective bush for the hole, as the joint is in constant use. Spacer tubes 74 (Figs. 8 and 11) are inserted into the end of the tube 2 or 3 and are positoned in alignment with each pair of opposed drilled holes. The tubes 74, thus disposed diametrically in the tube 2 or 3, are secured in the tube by bushes 75, carefully pressed into the ends of the tubes 74. The pivotally connected brackets 55A, 56A and 55B, 56B are now joined to the cross bea. A bolt 76, 76A is passed through each spacer tube 74. The bolt 76 further from the end face of the tube 2 or 3 also passes through the aligned holes 65, 69 of both brackets. The other bolt 76A passes through the holes 64 of brackets 55A and 55B. A nut 77 is engaged on the threaded end of each bolt. The nuts are tightened, only moderately at this stage, enabling the brackets 56A and 56B to be rotated about the bolt 76 on bush 76. The cross-beam 2 or 3 is now joined to the jull beam 5. The latter is located in blocks and the cross-beam and its attachments are lowered onto it, with the end of the cross-beam aligned with the face 53 of the hull beam. In this position the flange 67 of each brackets 56A, 56B is adjacent to the side face 54 of the hull beam 5 and the mounting portion 57 of each bracket 55A, 5B is adjacent to the side face 53. The brackets 56A, 56B are first bonded and then rivetted to the face 54. If the brackets 55A and 55B are not precisely aligned with the face 53 they may easily be deformed into augment, prior to bonding and rivetting to the face 53. It will be appreciated that this method of assembling the apparatus is applicable to hull beams whose faces 53, 54 are not perfectly parallel. This adaptability arises from the fact that the brackets 56A, 56B may be rotated about the axis of the bolt 76 prior to the fixing of the brackets to the hull beam, and from the fact that the brackets 55A, 55B may be deformed into alignement with the face 54. Once all four brackets have been fixed to the hull beam the nuts 77 are fully tightened on the bolts 76, 76A. Manipulation and tightening of the bolts and nuts is facilitated by using moulded nylon nut retainers 78 under the heads of the bolts and to receive the nuts, these retainers having a hexagonal recess to receive and grip the hexgonal portions of the bolt heads or nuts. The bridge portions 11 of the first brackets with the flanges, together with the bead zones 10 and the upper parts of the mounting portions 7 act as fairings and help to give the joint a neat appearance. In a modified construction, the brackets 55A and 55B are formed from a single plate of metal of squat T-shape, the stem of which forms a rectangular common mounting portion 57 shown in chain-dotted Tine outline in Fig. 8 and extending up to the level of the top of the brackets 56A and 56B. The two arms of the T-shaped plate are bent at right angles to the mounting portion to lie in vertical planes on each side of the tube 2 or 3 and thus from the bridge portions equivalent to 62A and 62B but extending vertically downwards to just above- the top surface of the level beam. The rivet positions are shown at X in Fig. 8. One half of the outline of the plate, before bending, is shown in chain-dotted outline 79 in Fig. 12. Figs. 14 to 16 show a rudder assembly which is particularly suitable for the catamaran described above but may be used on other boats. A transom 4 is rivetted to the aft end of the hull beam 5 and carries upper and lower pintles 85 and 86 for the gudgeons 87 5 and 88 of a rudder stock 89 consisting of two flat parallel plates rivetted to the gudgeons 87 and 88. A hydro-foil rudder blade (of which only the upper mounting part 90 can be seen in Figs. 14 and 15) fits between the two plates of the rudder stock 89 and is 10 pivoted to them by means of a cross tube and bolt arrangment 91. The rudder blade can thus swing from the position shown in full lines to the position shown in broken lines but is constrained to turn with the . rudder stock. 15 A hinged linage 92 has the lower end of its lower link 93 pivoted at 94 to a lug 95 on the rudder blade 90. The upper link 95 is effectively cranked to have a forward extension 96 which is pivoted at 97 to the top of the rudder stock. The upper length 95 has an upward 20 extension 98 which is connected by a length of line 99 formed with a hand grip kno 100 to a mounting staple 101 near the forward end of the tiller arm 102 rivetted to the rudder stock plates. On each side of the rudder, elastic cord 103 formed 25 into an endless loop extends forwards from " pulley-like mountings 104 on the hinge pivot 105 of the linkage 92 to similar mountings 107 fixed to the rudder stock plates 83. The operative position of the rudder blade 90 is 30 determined by a stop 111 against which the underside of the portion 96 of the upper link engages. The stop 111 is vertically adjustable, for which purpose it is secured between the two rudder stock plates by a cross bolt 111' passing through the stop 111 and through "35 vertical slots in the rudder stock plates. In use, if the rudder blade should hit an underwater object or a sharp pull is exerted on the line 89, the upper link will be swung about its pivot 97 with consequent stretching of th ecords 103 until the hinge 105 passes the line connecting the points 107 and 97 after which the tension in the cords will continue upward swinging movement of the rudder blade 90 until it abuts a further stop 112. The rudder blade 90 may be restored to its operative position by rotating the upper link 95. When launching the boat in shallow water, an intermediate position for the rudder may be obtained in which the toe of the rudder blade is just in the water. For this purpose the forward end of the line 19 is looped over the forward end of the tiller arm 102, 123 as shown in broken lines in Fig. 14. As shown in Figs. 15 and 16, the tiller arms 102A and 102B of the catamaran are interconnected by the connecting tube 9, the ends of which are pivotally connected to cranked pivot pins 122, the horizontal portions 123.of which pass through the tiller arms to be secured by a nut 124 and a welded-on collar 125, on opposite sides of the tiller arm 102. The precise position of the pivotal connection (i.e. of the upright portion 126) may be adjusted by selection of the number and thickness of shims 127. With this arrangement, a form of Ackermann Steering is obtained. A central tiller handle 128 is pivoted to the centre of the connecting tube 9. The ends of the connecting tube 9 rest on washers 131 (Fig. 16) welded to the vertical portions of the pivot pins. The projecting upper ends of each such pin has a " groove to fit in the narrower part of a keyhole shaped opening in a retaining plate 132 connected by a line 133 to the staple 101 to prevent loss of the plate 132. To avoid accidental separation of " each rudder from its hull, each transom 84 carries a spring catch 134 formed by a leaf spring rivetted to the transom and normally projecting over the top of the lower gudgeon 98. The catch can easily be pressed flat agianst the transom when it is desired to remove the rudder... OMPI

Claims: CLAIMS 1. An inflatable hull structure for a boat, comprising an elongate inflatable hull tube, and a rigid tubular hull beam, the undersurface of the hull beam having a channel which in cross-section has..an entry portion of reduced width, the inflatable tube has an anchoring rib comprising a web portion extending into the channel through the entry portion and a bead portion within the channel, the bead portion being sufficiently large to be incapable of passing out through the entry portion of the channel, and the hull beam has, on each side of the channel, a support surface for the inflatable tube. 2. A hull structure according to Claim 1, wherein the undersurface of the hull beam is concave with the support surfaces inclined to each other at an obtuse angle. 3. A hull structure according to Claim 1 or 2 wherein the forward end of the inflatable hull tube tapers down to a forward end plate and is spaced from the hull beam, and a bow member formed with bow cheeks meeting at a sharp bow stem has a socket engaged on" the forward end of the hull beam in a manner resisting rotation and locates the forward end of the hull tube by means of interfitting conformations on the bow member and hull tube and securing means between the bow member and hull tube. 4. A hull structure according to any of claims 1 to 3 wherein the height of the web portion is increased at the aft end. 5. A demountable joint between first and second elongated structural members such as the hull beam of a hull structure according to any of the preceding claims and a cross beam, in which the first member has first and second brackets on opposite face portions thereof, the brackets extending laterally of the first member and each having an aperture to receive a respective f stening element by means of which the brackets may " be secured to the second elongated member at positions spaced apart along the latter, wherein the first bracket has an extension forming a bridge across the first element and extending to- a registration portion secured to the apertured part of the second bracket. 6. A demountable joint according to claim 5 wherein the said registration portion is formed with an aperture which is aligned with the aperture in the second bracket and a bush extending through these two aligned apertures to secure the extension of the first bracket to the second bracket and to form the aperture for the relevant fastening to the second elongated member. 7. A demountable joint according to claim 5 or 6, wherein the arrangement of first and second brackets is repeated on the first member in a position where they will be on the opposite side of the second member, the two sets being conveniently in mirror-image relationship. 8. A rudder assembly comprising a rudder stock for pivotal mounting on the stem of a hull structure, for example according to any of claims 1 to 4, a rudder blade pivoted adjacent its upper to the rudder stock about a horizontal axis, and an elastic linkage interconnecting the rudder stock in such a manner as to OMPI urge the rudder downwards when the latter is in a lowered operative position but to urge it to continue to swing upwardly after the rudder has swung upwards through a predetermined angle. 9. A rudder according to claim 8 wherein the elastic linkage comprising a hinged linkage connecting a point of the rudder blade below its pivot (when the rudder blade is in its operative position) to a point of the rudder stock above the pivot and elastic means acting between the point of the hinged linkage between its ends and the point on the rudder stock, the arrangement being such that when the rudder is in its operative position, the line of action of the elastic means lies below a line connecting the point of anchorage of the elastic means to the stock and the point at which the upper end of the hinge linkage is connected to the stock. 10. A rudder assembly according to claim 8 or 9 wherein a tiller arm is secured to the rudder stock substantially inextensible and a flexible member connects a leading part of the tiller to an upward extension of the upper part of the hinge linkage so that the rudder blade can be swung to its upper position by pulling on the flexible member. 11. A catamaran comprising a pair of spaced-apart hull structures, and two rudder assemblies according to claim 10, one pivotally mounted on the stern of each -hull, with the leading ends of their tillers pivoted to the ends of a connecting rod by means of a pivotal connection which is offset from the respective tiller in the direction towards the opposite tiller to provide a form of Ackemann steering.

Inventors: MONTGOMERY JOHN AYRTON, MONTGOMERY, JOHN, AYRTON
Applicants: CATAPULT CRAFT LTD, CATAPULT CRAFT LIMITED
Application year: 1983
Main classification: B63B7
IPC codes: B63B1, B63B7, B63H25