BACKGROUND Small working boats and cruising yachts require both a life saving vessel and a means to transport personnel from the boat/yacht to the shore. Currently therefore, both a small dinghy and a lifeboat must be carried. As well as requiring the purchase of two separate additional vessels, this also takes up valuable space when such space is at a premium. Efficient use of space in working boats and cruising yachts is important.

A second problem with boats in general is to provide maximum speed of progress through the water. This is particularly important in the case of a lifeboat for use where no rescue service is available since this is often a relatively small vessel with limited supplies of food and water on board which must therefore carry its occupants to land as quickly as possible. It is desirable that a lifeboat can be sailed to land from virtually anywhere on the surface of the earth within 10 days. It is also desirable to provide improvements to lifeboats. for example, in their weight, strength and buoyancy and to provide a vessel which protects the occupants, particularly in poor weather conditions. For similar reasons, it is desirable that the vessel can be rigged and derigged at sea.

The present invention seeks to substantially alleviate or circumvent these problems and provide alternatives to current designs.

Figure 1 shows a boat with a hull 12 and mast 14 and a sail 16 of a shape known in parts of Micronesia and the East Indies. The sail is often known as a "crab claw" sail, because of its shape, which is broadly triangular, with curved luff 18 and foot 20 edges.

Crab claw sails are used with vessels known as proas, which have a main hull, and a smaller second hull to act as a flotation device. A mast is mounted not far from the centre of the main hull and the crab claw sail is suspended from a yard slung slantwise from the mast and is loosely tacked at the front of the boat. Proas have a rudder at each end and the sail can be tacked to either bow; the sail is always to the lee of the mast and proas progress by alternating direction.

SUMMARY OF THE INVENTION According to the present invention there is provided a boat with a mast and a crab claw sail, wherein the tack of the sail is attached to the boat behind the mast. The sail may have a single point of attachment to the mast, and the mast may be unstayed. The boat may further comprise a demountable cover to, when mounted, substantially enclose an occupant of the boat, a foot edge of the sail clearing the cover when the boat is in a sailing configuration, so that the boat, with the cover mounted, can be sailed by the occupant from beneath the cover. The

tack of the sail may be attached to the boat by releasable fastening means and the sail may be attached to the mast by a pulley means which is releasably fastened to the mast. The luff and foot edges of the sail may be maintained in a curved configuration by a spar or spars under compression; one end of the spar may held within a pocket and the other end of the spar may be provided with means for attaching it to the sail material such that the sail material can be tensioned and the spar compressed. The mast may be releasably attached to the boat at the bow deck. One or both of the head and clew tips of the sail may be provided with a stiffened extension portion which can gyrate independently of the spar of the corresponding edge of the sail. There may also be at least one oar which is adaptable for use as a portion of the mast. The boat may be a lifeboat.

According to a second aspect of the invention there is provided a complete or substantially complete kit of components intended to be assembled into the boat of the present invention. According to a third aspect of the present invention, there is provided a method of sailing a boat with a cover to substantially enclose an occupant, comprising: providing the boat with a mast and a crab claw sail the tack of the sail being attached to the boat behind the mast so that the occupants can sail the boat from beneath the cover. According to a third aspect of the present invention there is provided a crab claw sail adapted for the tack of the sail to be mounted behind a mast of a boat in that at least one of the luff and foot edges of the sail is maintained in a curved configuration by a spar under compression. A spar may comprise a plurality of separable jointed sections. One or both of the head and clew tips of the sail may be provided with a stiffened extension portion which can gyrate independently of the spar of the corresponding edge of the sail.

Other aspects of the invention include a boat with a mast and a sail wherein the tack of the sail is attached to the boat at or behind the mast and wherein the sail has a single point of attachment to the mast; a boat with a mast and a crab claw sail wherein a luff edge of the sail and a foot edge of the sail meet, or would meet if extrapolated, at a point adjacent the mast, and wherein the upward inclination of the foot edge is such that when the boat is in a sailing configuration a cover located aft the mast is not fouled by the sail; a boat with a mast and a crab claw sail attached to said mast, wherein the mast is mounted at the bow of the boat; and, a bow assembly for a boat with a crab claw sail comprising a bowcap moulding including a fore deck, means for attaching a mast to said fore deck, and a sail tack point adjacent said means for attaching a mast.

The various aspects of the invention provide a number of advantages including a boat with a relatively small but efficient sail capable of fast travel; a boat with a crab claw sail which can tack without needing to reverse direction; a boat, particularly a lifeboat, which can be sailed from beneath a cover; a boat with a sail which can be easily righted should it capsize; a boat and sail which can be compactly stored; and a crab claw sail with improved tensioning and support of the sail material.

In one embodiment, the boat is configured for use as a ship to shore transport vessel, as a sailing vessel and a lifeboat. The boat has oars, a removable centreboard and an attachable cover substantially enclosing the occupants of the boat. The boat is adapted for propulsion by rowing and skulling and for sailing; one oar is adapted for use as an oar and as a steering device, another oar has a detachable blade and is adapted for use as an oar and as a mast;

and the boat is correspondingly adapted for use of these oars as a steering device and mast. When sailed one oar is used as a steering device and part of a second oar is used as a mast. The boat has a positive buoyancy and is adapted to be sailed with the cover attached. Preferably the boat is also adapted for propulsion using an outboard motor. The oars comprise one or more component parts; the component parts separately and as an assembled oar have positive buoyancy. Preferably the masthead has removable pulley means, releasably attached and retained in position at all mast orientations. Preferably the boat has flush sheet attachment or anchoring points comprising a recessed cavity traversed by a rigid rod. the rod preferably having bearing means to allow it to rotate, reducing friction on attached rope. Preferably the cover is a removable awning retained in a slotted track disposed on the gunwales. The boat may be provided in kit form.

In a second embodiment the boat has a main body and a detachable bow section, the dimensions of the bow section and the main body being so chosen relatively to one another that the bow section may, when not in use, nest within the main body of the boat. Preferably the boat is a lifesaving vessel. Preferably the bow section and the main body of the boat separately have positive buoyancy.

In a third embodiment, the crab claw sail is reinforced by one or more spar means comprising a plurality ofjointed sections; preferably a spar tapers from the centre to either end and is prebent to provide sail curvature by means of a tensionable attachment. The sail may be provided with an attachment point for a sheet such as a halyard. The spar means may have an other than circular cross-section, for example a triangular cross-section.

In a fourth embodiment the crab claw sail has stiffening means disposed at the sail tips. Preferably the sail has head and clew tips which are stiffened by means of battens. The head and clew tips of the sail may be extended. The leech of the sail may have increased curvature.

In a fifth embodiment the crab claw sail has a sharp leading edge such that vortex formation on the leeward side of the sail is enhanced, preferably by means of an attachment to the leading edge of a spar.

In a sixth embodiment the crab claw sail has buoyancy means. Preferably the buoyancy means comprises a foam buoyancy pad adjacent a luff spar of the sail. The buoyancy means provides the advantage that the boat can be righted after capsize without the need for the boat helm or crew to enter the water.

In a seventh embodiment the dimensions of the material forming the surface of the crab claw sail are no greater than those required by a greatest planar projection of the desired shape of the sail. Alternatively, the sail may be cut with additional material, the increase in dimensions being so chosen that the sail may more easily adopt an aerofoil shape rather than being confined to a substantially planar set. Preferably the tack of the sail is quickly releasable. This feature allows the boat to be more easily righted after capsize.

The various features of the embodiments of the crab claw sail provide a number of advantages including rapid rigging and de-rigging, a lightweight rig, a rig which can be assembled and taken down whilst at sea, and increased

sailing speed.

In an eighth embodiment the boat has a rowlock, closed at the top to provide a pear-shaped opening to receive an oar, that is having an opening with a substantially semicircular lower part and a more elongate upper part.

Preferably the upper part has a generally triangular configuration and has an uppermost point which is rounded with a radius of curvature less than of the lower part. The rowlock has a male coupling member which engages with a socket in a corresponding fixing element. Preferably the boat has a hole of ellipsoidal cross section in the gunwale so that the fixing element, which has one or more outwardly extending flanges, attaches to the boat when it is inserted in the ellipsoidal hole and rotated.

In a ninth embodiment the boat has joining means, joining two sections of the hull of a boat, wherein each hull section has a watertight joining face extending upwardly from the bottom of the hull to a point which, when the boat is in use, is substantially above the water line. One hull section may have a vertical slot which engages with a corresponding protrusion on the other hull section to provide lateral alignment of the two sections. One hull section has a horizontally mounted coupling member disposed substantially at the bottom of the hull section and extending longitudinally beyond the joining face of the hull section. The other hull section has a corresponding vertically mounted coupling member disposed on the joining face of the hull section, the two coupling members releasably interengaging to provide vertical alignment and support of one hull section by the other hull section.

Additional releasable fastening means are provided adjacent the top of the joining faces of the hull sections, holding the corresponding upper portions of the hull sections together. Preferably the vertically mounted coupling member comprises a male coupling member and the horizontally mounted coupling member comprises a corresponding female feature. The male coupling member may be chamfered.

Two or more of the different aspects of these embodiments may be combined with one another in any permutation.

FIGURES In order to promote a fuller understanding of the above and other aspects of the present invention, some embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a known boat with a crab claw sail; Figures 2a to 2d show side views of an embodiment of a boat according to the present invention, respectively, the boat when used as a sailing vessel, the boat when used as a lifesaving vessel, the boat when used as a ship to shore transport vessel, and the boat nested on a yacht; Figure 3 shows an embodiment of a crab claw sail according to the present invention; Figures 4a to 4c show respectively a top view of a starboard oar, a side view of a starboard oar, and an oar assembly joint; Figures Sa and 5b show means of attaching a mast to the bow of a boat, in outline and in detail respectively;

Figure 6 shows a mast head with removable pulley; Figures 7a and 7b show flush anchoring points, being respectively, plan and side views of a lifting point; Figures 8a to 8d show respectively, a male top part of a rowlock, top and side views of a female lower part of a rowlock, a rowlock fitted to a boat gunwale and a side view of an oar in a rowlock; and Figures 9a to 9d show respectively, a detachable bow section of a boat when attached to the main body of a boat. and side, plan and coupling member detail views of a hull joining means.

DETAILED DESCRIPTION Figure 2a illustrates a boat 30 with a hull 32, a mast 38 and a crab claw sail 40; the boat has a centreboard 33 (only part shown) and a water line at level 60. The boat may be steered using a conventional rudder or, where a multifunction vessel is envisaged, an oar 58 may be provided for steering. The mast 38 is attached to the bow section of the hull close to the tip of the bow and supports the sail 40 by means of a halyard 50 attached to the halyard point 51 of the sail. The hull of the boat may comprise two separable parts, a bow part 34 and a stern part 36, for ease of storage.

The crab claw sail 40 is generally triangular and although the edges of the sail may be straight, they are more normally curved in the manner shown. The edges 44 and 46 of the sail are supported and maintained in a curved configuration by spars, which are described in more detail below. The upper edge 46 of the sail is termed the luff edge and the corresponding spar is the luff spar; the lower edge 44 of the sail is termed the foot edge and the corresponding spar is the foot spar. Edge 48 is the leech edge of the sail; the upper tip 52 of the sail is termed the head of the sail; the lower tip 54 of the sail is termed clew of the sail. The forward lower corner of the sail is termed the tack 42 of the sail. The luff and foot spars will generally run most if not all the length of the corresponding edge of the sail. Illustratively the material of the sail is shown as a continuous sheet joining the luff 46 and foot 44 edges. However, apertures may be provided in the sail. For example, if the luff and foot spars meet at the lower corner (tack) of the sail, the sheet material forming the body of the sail need not extend up to this point.

In a preferred embodiment the sail has a single point of attachment to the mast, halyard point 51, which is located part way along the luff spar. The sail also has other points of attachment to the boat, a sheet point 56 and a forward point of attachment 43 located on the tack of the sail. Further points of attachment may be provided if needed. The tack 42 of the sail is preferably attached by point of attachment 43 to a sail tack point (not shown in Figure 2a but shown as 118 in Figure 5a) on the fore deck of the hull 32. However, some of the advantages of the boat may be realised by attaching the tack of the sail to the mast of the boat (so that there are two points at which the sail is attached to the mast), rather than directly to the hull. This may be done by, for example, providing a collar or flange on the mast to which the sail tack can be attached. The tack of the sail need only be marginally behind the mast, how far depending partly upon the sail shape, in order to provide the functional benefit of a boat with a crab claw sail which is able to tack without reversing direction.

A mainsheet (not shown in Figure 2a) can be attached to sheet point 56 to allow an occupant of the boat to control

the sail. An occupant of the boat can lower the sail by letting out the halyard 50, for greater driving force when close-reaching. The halyard will normally be attached to the top of the mast although a lower point of attachment is also contemplated. Some of the advantages of the described embodiments may be realised by providing a sail of arbitrary shape with a single point of attachment to the mast and with the tack of the sail behind the mast. For example the sail may, with appropriate support, be triangular or diamond-shaped with a halyard point located at one corner of the sail; alternatively the sail may have more than four sides.

Conventionally a crab claw sail tacks forward of the heel of the mast. A disadvantage of this arrangement is that when the boat changes between a port and starboard tack or vice-versa, the tack of the sail must released and the sail moved aft and around the mast. In the present configuration the tack 42 of the sail is behind, or at least coincident with, the mast. This permits the boat to tack and gybe without the necessity of unfastening the base of the sail from the hull of the boat. The sail is normally entirely behind the mast, although when sailed part of the sail may be in front of the mast.

The mast 38 is mounted in the bow, preferably in a forward part of a fore deck of the boat, substantially adjacent a prow of the boat. The combination of this together with the manner of attachment of the sail to the boat and mast is advantageous since it properly positions the centre of effort of the sail (about 30cm in front of a centre board of the boat). Positioning the mast towards the front of the bow is convenient as well as functionally beneficial since it provides additional space in the centre of the boat.

Mounting the tack of the crab claw sail behind the mast provides the additional advantage that the mast can be relatively short, since the sail may be supported at a position half-way or less along one edge of the sail from the tack. In a preferred embodiment the mast is less than half the length of the luff edge of the sail. The mast can be unstayed and it is preferably made from a strong material such as carbon fibre. A short mast allows the number of separate components of the boat to be minimised since, for example. an oar can be adapted for use as an oar and as a mast. In one embodiment the mast is releasably attached at a bow deck of the boat.

The sail could be hung from a luff spar and provided with a corresponding foot spar, but with the relatively high position of the sail this arrangement would not provide good support. However, support and tension for the sail material and advantageous curvature of the spars can be provided by compressing one or both spars. This better maintains the shape of the sail when the sail is attached to the boat behind the mast and assists in maintaining the sail's planar form in such a configuration (see below). Since a spar can be made in a number of jointed sections (facilitated by the spar being under compression), because the mast can be short and because a crab claw sail is more efficient than a standard sail and can therefore be smaller, the entire rig can readily be held by a one or 1.5 metre long sail bag.

Figure 2b shows the hull of the boat with a cover 61 to enclose an occupant or occupants. The cover, illustrated diagrammatically, is preferably in the form of a demountable awning. The boat may be hove-to with the cover in place to provide enclosing protection for the occupants when weather conditions do not permit active progress.

The features of the boat and sail herein described allow rapid rigging and de-rigging at sea and Figure 2b illustrates the boat in a de-rigged condition. However, the shape of the sail and its orientation (the relatively high upward inclination angle of the foot edge) together with its forward position assisted by the mast position, allows it to clear the cover when the boat is in its sailing configuration. The boat can therefore be sailed whilst the awning is in place. a mainsheet running to a counter in the aft of the boat and thence to the crew, who are protected under the awning. In one embodiment the boat can be sailed, with the cover in place, in apparent winds up to 20 knots. This is not possible with a conventional sail design where the sail is mounted in a relatively low position and the boom and awning would obstruct one another. This is a particular advantage when the boat is operating as a lifeboat.

The awning provides protection from inclement weather and from the sun in hot climates. It may be made from a variety of materials including opaque, reflecting translucent or transparent materials but is preferably opaque, coloured air-sea rescue orange and provided with circular transparencies as window means. Metal foil may also be incorporated to improve visibility and/or reduce heat radiation/reflect excessive heat. The awning is preferably shaped by two polycarbonate arches which allow it to be flicked up over the boat or down into the hull. The awning preferably makes a substantially watertight fit with the boat; the top of the awning may include buoyancy to assist righting should the boat capsize. The boat itself is preferably also provided with positive buoyancy; in one embodiment it has a positive buoyancy of more than 900 pounds.

Given the aim that the boat be able to sail to land, which may be up to a thousand miles distant, within 10 days, the boat must be able to travel at approximately 100 miles per day. The speed of a boat which is not planing is determined by Froude's law and depends upon the length of the water line 60. The water line is low, in part because of the buoyancy, and the stern is shaped to give a maximum length of water line and hence a maximum boat speed under "normal" sailing conditions. The bottom of the boat is relatively flat so that it will easily plane, a small longitudinal ridge providing directional stability. To better cope with surf the bow is high, and for easy steering, the stern is not over wide. The hull of the boat is arranged so that two people can lie full length side by side on the floor to allow rest in an emergency situation. In bad conditions the boat can heave to with the cover up and a sea anchor out.

Figure 2c illustrates the boat in a configuration suitable for use as a ship-to-shore transport vessel. In this configuration the boat may conveniently be propelled by rowing.

Preferably bow part 34 of the hull detaches from stern part 36, which comprises the main body of the boat, and nests within it. Conveniently bow part 34 may be stored aft of a main seat with the bow pointing aft; Figure 2d shows the boat when stowed on a "mother ship" 63 such as an ocean-going yacht. This advantageously reduces the space required to store the boat - for example, a 3 metre boat can be stowed in a length of less than 2.5 metres.

Advantageously both bow and stern parts are provided with air spaces for buoyancy so that they float; some buoyancy is preferably incorporated in the gunwales.

Figure 3 shows an improved crab claw sail 40 embodying certain aspects of the present invention. The improved

sail provides a number of advantages, including easy rigging and de-rigging, light weight (an entire right for a small boat may weight under 15 pounds) and compact storage.

Referring to Figure 3, and considering first features of the spars, a luff spar 62 is fitted to the luff edge 46 of the sail and a foot spar (not shown) is fitted to the foot edge 48 of the sail. Each spar preferably comprises a plurality of jointed sections. The luff spar is shown as collapsible into three component portions 64, 66, and 68, although two or four or more sections could be employed. The foot spar is similarly collapsible. In a preferred embodiment a spar is constructed from fibreglass but other materials, for example plastic, capable of limited flexion without breaking can be used. A tubular spar of circular cross-section is preferred although tubular or solid rod of circular, oval, triangular or other cross-sectional form could be employed. The spar portions are configured to permit their assembly into a spar and to permit subsequent disassembly. Preferably their joining ends have male and female push-fit coupling elements, one spar enclosing the end of another; the male and female elements may have co- operating screw threads for increased strength. Alternatively the spar sections may be joined by a bayonet, screw, clip and eye or other means. A spar is fitted to the sail in such a way as to allow a compressive force to be applied to the spar which constrained by its attachment to the sail, adopts a bowed configuration. Simultaneously this tensions and provides support to material 82 of the sail surface, which improves the sail's performance and assists in achieving a planar set (see below). For increased flexibility a spar may taper towards one or both ends.

The luff and foot edges of the sail are preferably reinforced and provided with a plurality of sleeve enclosures 70 to receive the luff and foot spars; these may be folded tape pockets and may themselves provide the reinforcement.

The enclosures nearest the head and clew tips of the sail are provided with webbing pockets 74 to capture the ends of the luff and foot spars and to substantially constrain these ends from moving towards the tips of the sail.

At the end of each spar closest to the tack 42 of the sail means is provided for attaching the end of the spar to the material 82 of the sail such that the sail material can be placed in tension and spar in compression. A preferred embodiment will be described in relation to the luff spar; the arrangement for the foot spar is similar. In a preferred embodiment component portion 68 of the luff spar is provided with an attachment point 76, such as a metal loop, at one end and a second loop 78, such as a D-ring, is provided on a reinforced part of the sail. A cleat 80 is also provided on a reinforced part of the sail, positioned further from the tack 42 than loop 78. Both loop 78 and cleat 80 should be further from tack 42 than attachment point 76. The reinforced portions of the sail may be provided by the material forming the spar enclosures. When the sail is assembled, the luff spar is guided along the luff edge of the sail through enclosures 70 and one end is received by pocket 74. A rope is attached to one of loops 76 and 78 and is passed through the other loop; to provide a mechanical advantage, the rope may be passed through the pair of loops 76 and 78 a plurality of times. The free end of the rope is then pulled tight to urge loops 76 and 78 closer together. The head end of the spar is held by pocket 74 and prevented from moving substantially further towards the head tip of the sail and hence the spar is compressed and adopts its curved configuration and the sail material is tensioned; the rope is then fixed using the cleat. The arrangement may additionally or alternatively include a block and tackle and/or a sliding car in a track or luff groove.

A halyard and mainsheet can be attached to the sail by providing a point on each of the luff and foot spars with a metal loop. If the spars are tapered, this can be provided by a ring incorporating an Inglefield clip, whereby the ring slides along the spar and is force fit at a point determined by the spar taper, where the inside diameter of the ring is substantially equal to the outside diameter of the spar. Alternatively a ring can be fastened at a chosen position on the spar, for example through the spars' leading edge. Access gaps 72 to the attachment points are provided between spar enclosures 70. A preferred alternative is to provide reinforced holes - cringles - in the sail material near inside edges of the luff and foot spars, preferably between a third and half way along the appropriate sail edge from the tack. These attachments provide strength, flexibility and light weight.

The tack of the sail is attached to a fore deck of the boat by means of forward point of attachment 43. In the preferred embodiment described above the luff and foot spars do not extend to the tack 42 of the sail and point of attachment 43 is provided by a further cringle. This is located in the general vicinity of the point where the luff and foot spas would meet if they were extrapolated. If, in an alternative configuration, the luff and foot spars meet or connect. their meeting or connection point may provide a point of attachment. The point of attachment 43 is attached to sail tack point 118 (shown in Figure 5a) by means of, for example, an Inglefield clip, an encapsulated, quick-release shackle, a sheet or other conventional means. (An Inglefield clip comprises two metal loops arranged to releasably interconnect with one another, releasing by turning one loop through 90" relative to the second and pulling). An Inglefield clip attachment allows the tack of the sail to be quickly released from the boat, if necessary.

Other than shape and greater efficiency, two significant differences between the present sail and conventional triangular sails are: (i) The sail is attached to the mast at one point only (the halyard point) on the luff of the sail whereas conventional triangular sails have the entire sail luff attached to the mast; and (ii) When the sail is set at an angle of between 400 and 1500 to the apparent wind the sail trim is substantially planar whereas conventional triangular sails are set as aerofoils. At these larger angles a crab claw sail provides a greater and more readily predictable driving force than does a Bermuda rig.

The sail is preferably cut flat, that is, it is cut so that the material of the sail may be laid on a flat surface substantially without stretching or wrinkling the material of the sail. This can be expressed more scientifically by requiring that the dimensions of the material forming the surface of the sail are no greater than those required by a greatest planar projection of the desired shape of the sail. The sail material 82 may be of any conventional type; synthetic fabrics based upon polyester or polyamide are usual. Reefing means may be provided, in a preferred embodiment a plurality of reinforced apertures 85 disposed at intervals along a line of similar curvature to the foot edge of the sail and diverging from the foot edge with increased distance from the sail tack. In one embodiment the distance 92 from the tack to the mid-point of the leech 48 is about 1.7m and the corresponding cord width 94 of the sail is approximately 2.4m. Camber lines 83 may be marked on the sail.

The planar set and the delta planform shape of the sail causes vortex flows to form over the leading edge spar on the leeward side. The vortex formation helps maintain attachment of the flow to the extremities of the sail and reduces drag. Wind tunnel tests have indicated that the force provided by a crab claw sail is weakest when close-

hauled. At less than 40° to the apparent wind (for example, between say 28° and 40°) the sail can be allowed to deviate from a planar form. This can, if so wished, be enhanced by cutting the body of the sail so that instead of lying flat it has some in-built aerofoil shape, for example, an extra 4 to 6% allowance being made. In this way for close-hauled and/or windward sailing the sail can be set and trimmed as a conventional foil and when the sail is at greater than 40° to the apparent wind, the mainsheet can be used to apply force to the foot spar to stretch the material of the sail so that it becomes substantially flat.

It is desirable to promote and maintain the vortex formation mentioned above and it is believed that providing the sail with "winglets" - stiffened extension portions 86 at the head 52 and clew 54 tips - can assist this. A winglet should preferably be able to gyrate independently of its adjacent spar to assist the vortex flow and hence a spar preferably does not extend up to the point of a sail tip but is retained by a pocket 74 at a position where the general curve of the leech would if extrapolated, intersect the sail edge. The winglets may be formed from sail material which is only loosely coupled to the main body of the sail or the material of the body of the sail may be cut to increase the curvature of the leech 48 to provide effectively longer and more sharply pointed head 52 and clew 54 tips. An extended tip may be stiffened by means of a removable batten 88 held in a shaped enclosure and captured at one end by a pocket 90. Part of the length of a batten should preferably overlap an end part of its adjacent spar so that in a quiescent condition the tip is held generally in the plane of the sail.

The stiffened tips of the sail are intended to emulate the function of the upturned feathers seen on the wing tips of large birds of prey. They seek to provide reduced drag and increased forward force for a given wind strength. It is believed that the spar on at least the leading edge of the sail generates vortices on the leeward side of the sail and that these vortices serve a number of functions, including helping to maintain attachment of the airflow to the sail, in particular at the extremities of the sail. The vortex flows exhaust aft and without proper exhaust of the dead air inside the vortex pressure increases on the leeward side of the sail, forward suction is diminished and the speed of the boat drops. It is thought that the exhaust flows of dead air from the centre of the vortices are assisted by providing a route by which air from the inner core of the vortices can stream out from behind the sail, and that this results in a smoother, more controlled and controllable air flow and hence enhanced and more predictable forward force over a wider range of sail angles.

The sail can be further improved by "sharpening" the edge of one or both spars. If the wind sees a sharper edge, it is believed that vortex formation is enhanced. Wind tunnel tests suggest that sharp edges on delta wings assist vortex formation on the leeward side of the wing. On the sail, sharper leading edges create more controlled suction and allow vortex formation to take place at a greater angle of incidence to the apparent wind. Such edges can be provided by, for example, attaching a polyethylene extrusion to the leading edge of a spar. The extrusion preferably has a triangular or arrow-shaped cross section although any shape which presents a sharp edge to the wind, even a suitably attached flat strip, could be employed. A preferred version has a "V"-shaped cross-section with a base width of approximately 1 inch (2.5cm) and a height to the apex of approximately 2 inches (Scm). If desired, the extrusion can be permanently attached to the edge of a spar by means of, for example, sections of heat- shrinkable tubing.

Buoyancy means such as sewn-in foam buoyancy pad 84 may also be advantageously provided on the sail, to help keep the sail afloat and hence to make it easier to lift out of the water. This is particularly important should the boat capsize. With a conventional rig the sail is attached to the mast along the length of the luff edge and should a small boat capsize, because of the weight of the rig and the "suction effect" of the water around the sail, the helm and/or crew must climb onto the centreboard to lever the boat upright. In rough conditions this can be very difficult and when offshore it is undesirable to have to get into the sea because of the risk of cold and exposure and, in warmer latitudes, sharks. However the present boat requires little leverage to bring it upright - the short mast, the greater efficiency and hence relatively smaller size of the crab claw sail and its single point of attachment to the mast make it unnecessary for the crew to enter the water to right the boat should it capsize. By letting out the halyard the sail can be eased from the mast leaving it in the water whilst the boat is righted, and afterwards the sail can be withdrawn from the water. A floatation patch on the sail assists this procedure.

The boat has oars which are multifunctional and collapsible - one of the oars breaks down into three sections and can be used as an oar for rowing or, with the blade unscrewed and removed, as a mast; the other breaks down into two sections and can be used as an oar for rowing or as a steering oar. Figures 4a and 4b show top and side views of a starboard oar 96. The oar is preferably made from fibreglass although other suitable materials, for example wood or plastic, can alternatively be used. The oar comprises a shaft 98 and an oar blade 100; preferably the blade is detachable from the shaft so that the shaft can be used for mast 38. The shaft is separable into two section, 102 and 104, to reduce its length for ease of stowage. The port oar is sitnilar to the starboard oar except that the blade may be permanently attached to its shaft; the port oar may serve as steering oar 58 when the boat is being sailed.

The oars and their separate component parts are preferably configured to be watertight and to float. Figure 4c shows a section through a preferred means for joining a blade 100 to a section 102 of shaft 98, which permits secure assembly and subsequent disassembly. Blade 100 is provided with a male spigot 101 which fits into female sheath 103 of oar shaft section 102 and the blade and shaft section are provided with screw fastening means. Shaft section 102 is provided with a grade 316 or 304 stainless steel threaded rod 106 with a nut attached, the rod and nut being set into a resin compound 138 which holds the assembly in place within the oar section. Rod 106 co-operates with matching threaded opening 108 and spacers 110 and 112 abut when the join is tight. Similar joining means can be used to join shaft sections.

Mast 38 may be attached to the bow of the boat by any suitably strong means; advantageously the mast is unstayed.

Figures 5a shows a section through a bow portion of the boat, illustrating a preferred mast attachment and sail tack point 118. The mast attachment illustrated is configured to allow removable attachment of the shaft of the appropriate oar - as described above, the starboard oar - so that there is no need to provide a separate oar when the boat is sailed rather than rowed. The mast is assembled by unscrewing the oar blade and screwing the oar shaft securely into a mast receptacle. Bow part 34 of the boat includes a bow assembly comprising bowcap mould 114 the upper surface of which provides fore deck 116. An annular aperture 120 in the fore deck receives sheath 103 of shaft portion 102 of oar 96 (which will become mast 38). Bow part 34 includes buoyancy tank 122, the forward portion of which is raised in a step to provide support for the mast attachment and to urge the boat to float higher

up out of the water when upside down. The bow part of the boat further comprises recessed sail tack point 118 and towing point 128, described below.

Figure 5b is a detail view of the mast attachment, which is located in a region 115 of the fore deck near the prow of the boat. A portion 130 of the bowcap moulding surrounds tubular strengthening sleeve 132 forming a mast receptacle which locates on buoyancy tank moulding protrusion 124. A central male spigot 126, similar to the spigot of oar blade 100, is provided in the mast receptacle, preferably flush with the fore deck. Spigot 126 includes sleeve 127, glass reinforced plastic (GRP) reinforcing material 125 and a threaded aperture set into a resin compound 134; the aperture may comprise one or more nuts 133 embedded in the resin. When the mast is attached to the boat the aperture receives threaded rod 106 and carbon peg 136 helps to prevent resin compound 134 from turning as the mast is tightened.

The efficiency of a crab claw sail depends upon the wind direction and the sail's orientation. The mast can advantageously be raked back so that the angle 'M' the mast makes with the fore deck is less than 90 degrees. The rake may be up to 30 degrees from the perpendicular; preferably angle 'M' is approximately 80 degrees. As illustrated in Figure 2a the sail is in a high position although since the sail has a single point of attachment to the mast it can be lowered by letting out the halyard, which increases the sail's efficiency when reaching. In one embodiment the boat can be sailed from 28 degrees to windward.

Figure 6 shows a masthead device comprising a swivelling pulley assembly to facilitate attachment of sail 40 to mast 38. The device, which comprises mast insert 140, hook 142, halyard block 144 and spring means 146, is releasably clipped to the top of the mast. The hook attaching the halyard block is readily removable but resists being pulled out of the top of the mast should the boat capsize. When the sail is attached to the mast, halyard 50 passes through halyard block 144 and is fastened to hull 32, for example, at sail tack point 118. Mast insert 140 is preferably solid and permanently attached to the top of the mast, for example, by glue. It may be formed from glass reinforced plastic (GRP) or a synthetic polymer such as polyvinyl chloride (PVC). The mast insert has a blind opening in the top to receive one end of stainless steel hook 142; the other end of hook 142 captures block 144.

The hook is retained in the insert by stainless steel spring 146 which bears against a rim of the insert and the halyard block is therefore retained on mast 38 should the boat capsize.

Figures 7a and 7b show plan and side views of a rope or sheet attachment point for the boat. In Figure 7 the rope or sheet attachment point is located in a gunwale but the attachment point is suitable for use as a general purpose rope or sheet anchoring point and as a point through which a rope or sheet can be guided. It comprises recessed slot 150 traversed by a rigid tube or rod 148, preferably with bearing means such as sleeve 152 to minimise wear on the rod when a rope is attached. Preferably the rod is made from GRP and the bearing sleeve is formed by wrapping an exposed part of the rod with Kevlar cloth which is heat-treated to form a tube. Other suitable materials for the rod include 304 and 316 grade stainless steel and solid PVC, and for the bearing sleeve polyamide (for example, Aramid). The attachment point avoids weight and abrasion problems associated with conventional fittings which comprise metal standing proud of a hull and which can rub against the upper works of a parent yacht

when a boat is stowed. Preferably a plurality of such attachments is provided, including at four lifting points on the flotation coamings, at sheet lead points on the stern, abaft the heel of the mast at sail tack point 118, and at bow towing point 128.

Figure 8 shows a rowlock 154 for the boat with two components, a male top part 155 to receive an oar and a female lower part 159 to attach to the boat and to receive the male top part. The rowlock has an upper part 156 which is closed at the top to provide an "egg" or "pear" shaped opening, whereby an enclosed oar 96 is permitted to move in a vertical axis as shown in Figure 8d. Conventional rowlocks which are open at the top carry the risk that an oar may be lifted out of its crutch and carried away, whilst round rowlocks provide only limited vertical movement which has the disadvantage that when a boat nears land an oar may strike ground and lever a rowlock off the gunwale. The raised and pointed crown of the rowlock's circlet shown in Figure 8a alleviates this problem.

A further advantage of the rowlock is that it can be attached to a boat without the need for screws, bolts or similar fastening means. Male top part 155 is provided with a male spigot 157 configured to engage with a corresponding aperture 161 in the female lower part, shoulder 158 abutting upon rim 160 in the assembled rowlock. The female lower part is provided with fixing flanges 162 whereby, when inserted into an ellipsoidal mounting hole 164 and rotated the fixing flanges engage with side of the hole and lock the part in place. The part 159 may then be further secured with glue. The top part 155 of the rowlock may also be fastened to the boat, for example by means of cord passing through the base of the female lower part 159. The rowlock may be fabricated from a variety of materials including gun metal, bronze and plastic. Preferably each side of the boat is provided with a rowlock and a further similar rowlock is recessed in the stern to provide support for a steering oar. Figure 8c shows a section through a gunwale 166 on which the rowlock 154 is mounted; the figure also shows a lifting point 168 and a moulded-in track 172 for an awning or cover for the boat.

Advantageously the hull is constructed from fibreglass with a "honeycomb" structure for lightness and strength.

Further layers of biaxial material and Kevlar (Aramid fibre) tissue provide stiffness, and abrasion and impact resistance respectively. The awning track is pre-formed as a plastic, GRP or aluminium rod or tube 170, laid up with the main hull, and then provided with slot 172 for a bolt rope awning edge.

Figure 9a shows the forward part of the hull 32 of the boat with bow part 34 attached to stern part 36 of the hull along join line 35. The two parts of the hull can be assembled on a firm surface or in the water by removing the bow part from its stowed position, locating it on the front of the boat as described below, to connect the lower part of the join, and then by using fastening means such as wing nuts and bolts (not shown) to securely connect the upper part of the bow and stem join.

Referring to Figure 9b, both bow part 34 and stern part 36 of the hull have a bulkhead surface, respectively surfaces 196 and 194, extending upwardly from the bottom of the hull and extending laterally between the exterior surfaces of the hull on either side of the boat, to prevent ingress of water and to providing matching surfaces for alignment of the join. These bulkheads may extend the full height of the hull but preferably extend from the bottom to half

the height of the hull and are provided with corresponding parts of one or more wing nut fastenings at the top. The bow and stern parts are configured such that when joined they present a substantially continuous hull surface 192 to the water. Stern part 36 is provided with a bulkhead slot 174 with which a matching protrusion 176 on bow part bulkhead 196 engages, laterally aligning the two parts. The slot and protrusion do not extend the full depth of the boat and hence also provide basic vertical alignment of the two parts. Figure 9b does not show detail of the lower part of the join; line A-A indicates the height of the plan view of Figure 9c. Figure 9c shows a plan view of the join including a top view of metal plate 178 attached to the bow part; line B-B indicates a medial line of the hull.

Figures 9d shows details of the lower part of the join; lines L and M show the motion of the bow part as it is attached to the stern part of the boat. A vertical stainless steel locking plate 178 is fastened by bolts 180 to the lower part of the joining face of the bow section, face plate 190 enhancing the strength and integrity of the joint.

The lower part of plate 178 is provided with a male coupling element, alignment pin 182, for engagement with a corresponding aperture 188 in the stern part. A second steel plate 184, provided with female receptacle 188, is fastened by bolts 185, and preferably a lock nut 186, to the base of the stern part of the hull of the boat, again with a face plate 190. Additional GRP moulding provides a shaped horizontal shoe 189 which engages with a corresponding recess 191 in the bow part. The bow and stern parts of the boat snap together, the male and female parts engaging to provide alignment and mutual support. In a preferred embodiment the locking plate and face plates are made from 8mm thick flat stainless steel bar tapped to take countersunk 8mm stainless steel bolts, although other metals, plastic or GRP may also be used. To ease alignment the lower part of the join may incorporate a chamfered rod to assist location of the locking plate 178 in the lower plate 184; alternatively the lower plate 184 may have a location groove or slot cut into or through it. For ease of alignment, the joint may be provided with two or three millimetres of slack.

Many other equally effective alternative configurations will occur to those skilled in the art and it should be understood that the present invention is not limited to the described and illustrated embodiments.