This invention relates to a sail and sail arrangement for craft which are at least partially propelled by wind power. It further relates to a method of imparting a curved shape to such a sail. It further relates to a craft having such a sail arrangement.

The invention finds particular use in providing sail arrangements for single or multiple hulled boats, although it will be appreciated that the invention may be used also for other wind powered craft such as land yachts, sand craft, windsurfers, etc. The invention also extends more generally to reconfigurable aerodynamic arrangements.

The performance advantage to be gained from using wing type rigs has been appreciated for some time, and several types of wing rig have been built, mainly for 'C class catamarans. These wing rigs have mainly comprised sections of substantially rigid symmetrical aerofoil sections. Although such sections can generate high levels of propulsive thrust (lift), their rigid structure means that the aerofoil section of the wing is fixed. It is also known to have multiple sections in which individual sections are fixed but can be moved in unison to adopt a required profile. Furthermore, their rigid structure means that reefing or stowage of the wing is either not possible or extremely cumbersome.

The present invention aims to provide a wing sail arrangement in which it is possible to change the shape of the wing sail to suit tack, wind direction and so on. A further aim is to allow the easy assembly of wing sails from standard materials including flexible sail cloth. Such sails may be easily disassembled for storage when not in use.

According to a first aspect of the invention there is provided a sail for a wind powered craft comprising :

I. a sail having a luff and being formed from overlapping first and second sail panels joined at or adjacent their leech edges and together forming a sail leech ; and

II. a plurality of battens located between the first and second sail panels to extend at least partially between the sail leech and the sail luff, means being provided to apply a load on the battens to force at least some of the battens to adopt a curved profile and impart a correspondingly curved profile or increase the curvature of an already curved profile to either the first or the second sail panel; wherein said battens can be moved from one sail panel to bear upon the other sail panel to enable the sail to be tacked.

The sail panels need to be joined to some extent at or adjacent their leech edges so that they may both interact with the battens to apply a load thereto. However, such joining may be at one or more discrete point or along one or more continuous lengths. Such lengths may extend some or all of the length of the sail from head to foot. The leech of a sail is not just the very edge and in the context of the present invention it can be said to comprise about 20% of the distance in from the leech of the sail. To be adjacent the joining will normally be within that region. Ideally the panels are joined at or adjacent a battens. The joining may be direct panel to panel or may be indirect through some other part such as a batten itself.

The set of battens located between the first and second sail panels are arranged to force an asymmetric aerofoil shape into the sail, and the battens are not connected to the inside surface of either sail panel over at least a significant middle part of their length. They may of course be connected to the sail adjacent the luff or the leech. The battens can be moved from bearing on one panel to the other to enable the sail to be tacked.

The load applied to the battens can be a lengthwise compressive load.

The load may also be a lateral load tending to increase or decrease the curvature depending on the direction of action on the batten.

Said means to apply a load on the battens may allow adjustment of the load on the battens and the resultant curved profile of the battens while the sail is in use to allow selection of an appropriate curvature of the sail. The adjustment means may allow adjustment of the curvature by varying the effective length of a batten relative to the luff-to-leech distance of the sail in the vicinity of that batten. Alternatively said means allows adjustment of the curvature by varying the effective length of the luff-to-leech distance of the sail in the vicinity of a batten. Battens may be formed from batten elements that may be laterally forced apart or together to alter curvature. Those batten elements may be overlapping and they may be joined at their ends. The effective length (horizontally from luff to leech) may be altered by changing the angle of a batten between the panels. According to a second aspect of the present invention there is also provided a sail arrangement for a wind powered craft comprising: a sail as previously described; and a mast to which the sail luff is mounted so that the sail panels and battens extend from the mast.

The front of the sail or sail luff may be formed by the luff edges of the first and second sail panels which may be separate, joined or common. The luff may be located on or around the mast. Such a sail need not fix to any part of the mast but simply locate there around to form a pocket or envelope within which the mast locates. Alternatively the luff edges of the two sail panels may be connected to opposite sides of the mast. In certain embodiments the luff edges of the first and second sail panels may engage in separate roller furling mechanisms provided in or on the mast. The luff edges may connect a front sail panel that extends round the front of a mast and has appropriate formations to not foul parts such as forestays that extend from the mast.

The battens may be connected to the mast and connected to the sail at or adjacent the leech (which is the area adjacent the trailing edge of the sail). The connection to either end may be fixed or adjustable dependent on the arrangement. The battens may be mounted such that they are movable radially with respect to the mast only within a limited range of radial angles. This can help limit and control the degree of curvature imparted to the sail.

Said means for adjusting the battens may comprise a batten length adjuster provided in or adjacent the mast at or near the luff end of each batten. This may take many suitable forms such as a device that forces the mast end of a batten away from the mast. In an alternative each batten may be adjusted by providing two relatively hinged batten portions such that the length of a batten may be adjusted by altering the angle of the portions with respect to each other. Alternatively the means of adjusting the batten length may be provided by a lever system located at the leech end of the batten. Alternatively the means may be arranged to adjust the angle of each batten relative to the mast, within a plane containing the mast. In this way a batten that is longer than the horizontal distance between mast (or mast equivalent at the luff - such as a forestay) and the leech can be positioned at an angle and compressed or relaxed by altering that angle within the constraints of a fixed sail envelope.

The mast may also be used to adjust the battens. The mast may have a main section to which (or around which) the sail panels are secured and a sub-section to which the battens are mounted, the mast sub-section being movable relative to the mast main section. Such relative movement may be horizontal or vertical relative to the mast main section.

The sail may be arranged to allow adjustment of the curvature of each batten either simultaneously and/or independently. This allows a high degree of control over the sail curvature in different areas of the sail.

As well as adjusting the batten compression and sail curvature by altering the effective batten length it is possible to do so by altering the effective luff-to-leech distance of one or both the sail panels. Independent furling of the two sail panels as mentioned above is one way of achieving that.

Mounting means may be provided for the mast, permitting the mast to be rotated about its longitudinal axis thereby potentially changing the curvature of the battens and/or altering the direction of the leading edge of the mast. Such rotation may be about 360 ^Q or may be confined to a lesser angular range - suited for example to tacking. The mast may be generally elliptical in cross-section as this provides a leading edge of a desirable shape.

Fore and aft tensioning of the sail will exert compressive force on to the battens (or vice versa) causing them to distort. This, either alone or in conjunction with rotation of the mast and levered force on the battens within the mast section, will distort the battens to achieve a curvature and thus impart an aerofoil shape on the sail by exerting pressure on one of the sail panels.

The aerofoil shape of the sail may be altered by relative increase or decrease in the compressive force applied to the battens and associated tensile force applied to the sail panels. If the force increases the battens will distort further, and so increase the depth of cord of the sail. As it decreases the battens will bend less and the depth of cord will decrease.

Rotating the mast from one side to the other when tacking or gybing so that the leading edge of the mast points into the wind can cause the curved battens to invert their profile and/or move from applying pressure from one sail panel to the other panel within the envelope defined by the panels. This can be helped by the restraining force of a sheet on the leech foot.

The leech may be fixedly connected to the end of the battens. It is also possible that for reefing purposes the sail area may need to be reduced. One way of achieving this is for the point of connection of the sail leech to a batten to be adjustable along at least a portion of the batten's length. In this way the sail may be shortened such that the batten may extend beyond the leech edge but with the curving of that batten portion remaining within the sail still being possible, but on a smaller sail.

Different configurations of sail according to the present invention may be chosen dependent on performance priorities such as weight minimisation, reefing capacity and so forth.

According to a further aspect of the invention there is provided a wind powered craft having a sail or sail arrangement as described herein.

The present invention also provides a method of adjusting the curvature of a sail formed from overlapping first and second sail panels joined at or adjacent their leech edges and forming a sail leech and having a sail luff, and a plurality of battens located between the first and second sail panels to extend at least partially between the sail leech and the sail luff, in which method a load is applied to the battens to force at least some of the battens to adopt a curved profile or alter an already curved profile and thereby impart a correspondingly curved profile to either the first or the second sail panel.

The battens used in the present invention can take variety of forms and may be made from a variety of materials. They must exhibit the ability to adopt a curved profile or have their profile adjusted and lengths of resilient deformable material such as are use already as sail battens would be suitable. Battens may be curved in an un-loaded state. It would also be possible to use an inflatable batten. Such a batten could be inflated for use and then deflated for storage. An inflatable batten might be formed by an elongate sealed pocket defined by airtight material, which pocket when inflated gives the batten sufficient resilience that it can be curved like a normal batten. It would also be possible for the degree of inflation of an inflatable batten to control the degree of curvature of a batten. Potentially this could also allow the curvature to be altered by dynamic adjustment of the batten's inflation. A batten might be configured such that different chambers within the batten could be selectively inflated and deflated to change the degree and/or orientation of curvature.

In order that it may be better understood, but by way of example only, several embodiments of the present invention will now be described in detail with reference to the accompanying drawings in which:

Figure 1 is a horizontal sectional view through a first embodiment of sail arrangement (which herein may also be referred to as a wing sail) showing a batten in a non-loaded un-curved state;

Figure 2 is a similar sectional view through the same sail arrangement, showing the batten curved and giving the sail an aerofoil shape;

Figure 3 shows two sectional views through the sail arrangement of Figure 1 and 2. 3A shows the arrangement with the batten and sail panels loaded. 3B shows the same arrangement but with greater loading causing the batten to distort further, and the resulting aerofoil shape to adopt a deeper sectional profile;

Figure 4 shows a series of horizontal sectional views through the arrangement of Figures 1 -3 illustrating how in this version movement of the mast relative to the sail can force the batten to tack, reversing the profile of the aerofoil;

Figure 5 shows a horizontal sectional view of second embodiment of sail arrangement where a roller furling type systems within the mast is connected to the luffs of each sail panel;

Figure 6 shows a horizontal section view of the roller furling arrangement as described in Figure 5 with the batten and roller furling system tensioned;

Figures 7, 8 and 9 are schematic side views of a third embodiment of the invention showing stages of a sail being stowed or extended;

Figure 10 is a horizontal sectional view through the sail arrangement as illustrated in Figures 5 and 6 showing how the roller tensioning system may operate with levers attached to the foot of each sail adjuster;

Figure 11 is a horizontal section through a mast designed to work as part of a fourth embodiment of the sail arrangement. In this case two vertically elongate mast sections are arranged such that they are capable of movement in relation to one another horizontally fore and aft (in this view) such that they operate to increase or decrease the depth of the mast section;

Figure 12 shows the mast section of Figure 1 1 in a rearwardly extended form;

Figure 13 shows a view of an embodiment of mechanism by which a batten may be loaded by means of a cord attached to the batten;

Figure 14 shows a view of a different embodiment of mechanism by which a batten may be loaded using a lever tensioning device near the leech;

Figure 15 shows a schematic view of a further embodiment of wing sail; Figure 16 shows a further embodiment of batten formed from two pre-curved batten elements joined at their luff and leech ends;

Figure 17 shows one of the batten elements of Figure 16;

Figure 18 shows a cross section through the batten element of Figure17;

Figure 19 shows a horizontal section though a mast and sail envelope with an embodiment of batten as shown in Figures 1 6-18;

Figure 20 is a view similar to that shown in Figure 19 but showing an increased curvature;

Figure 21 shows a horizontal section though a mast and sail envelope with a yet further embodiment of batten which is inflatable;

Figure 22 shows the arrangement of Figure 21 with an increased curvature;

Figure 23 is a yet further embodiment with battens having mast ends that move vertically to alter the effective length to curve or relax the battens;

Figure 24 is an enlarged view of the outer end of one batten from the embodiment of Figure 23; and,

Figure 25 is partially sectional view of a possible mechanism for attaching the mast end of a batten to a mast for vertical adjustment as in the embodiment of Figure 23.

Illustrated in Figure 1 the sail arrangement has a mast section 1 into which a batten 2 enters at its aft edge 3 so that a portion 4 of the batten is accommodated within the mast section. Sail panels 5 made from deformable material extend from the rear end of the batten 6 to wrap around the mast section and return to the same batten end where both sail panels are held. The sail panels are made from a variety of suitable materials which include all available sail cloths and laminates.

The sail arrangement has no appreciable horizontal loading on either batten or sail panel. In this state the, or each, batten 2 sits in a relatively central location within the sail envelope and adopts a relatively straight configuration extending between the mast and the point where it connects to the sail panels. The part of the sail panel to which the batten connects may be the sail leech 7 or some part near thereto. Unlike other sail battens these are not contained within batten pockets connected to one or other panel of the sail. And it is a feature of this invention that the batten is able to move freely from contacting one sail panel to the other when the sail is tacked. Fig 1 shows how in this neutral position the only point of contact between the batten and the sail panels is at the leech.

Figure 2 shows the sail arrangement as described in Figure 1 however with mast rotated away from the neutral position and the batten loaded by extension thereof within the finite length of the panels. It shows the resultant change in the profile of the sail arrangement which is now wing shaped. It shows the sail arrangement with compressive loading on the batten and horizontal tensile loading to the sail panels. This loading may be achieved by either increasing the batten length relative to the distance between the point at which it is held against the mast and the leech or by shortening the sail panels relative to said distance (or both). The compressive loading applied to the batten causes it to bend and be forced against one sail panel, generally the leeward panel when sailing, to cause the sail arrangement to adopt an aerofoil shape in section. Additionally as shown in Figure 2 the shape of the mast section assists in achieving this aerofoil shape. The part of the batten within the mast section also assists in achieving this aerofoil shape. The way the leading part of the batten bears against the mast surfaces assists in a smooth transition of shape from mast to batten thus resulting in a suitable aerofoil shape.

Additionally the shape of the aerofoil may be adjusted by rotating the mast away from or toward the restraining force of the mainsheet (not shown) which is located beneath the sail leech 6. Rotating the mast away from the restraining force of the mainsheet causes the position of maximum depth of the aerofoil to move towards the leading edge of the aerofoil. More generally Figure 2 shows the sail arrangement on port tack when sailing. When sailing with this rig the mast will be rotated or allowed to rotate so that its trailing edge moves away from the wind direction 8. Figure 2 shows the windward sail panel as essentially flat. However, when sailing wind pressure on this panel will cause it to distort inwards slightly towards the centre of the aerofoil section. The relative stiffness of the battens and tensile resilience of the sail fabric will determine how much distortion occurs on the windward sail panel. The stiffer the battens or more resilient the sail fabric the less this panel will deflect.

Figure 3 shows how the depth of the sail section may increase or decrease depending on how much force is exerted on the batten and sail panels. Further the illustrations show how mast rotation may be adjusted to suit the shape desired of the aerofoil. 3A shows a more close handed profile relative to the more off-the-wind profile of 3B.

Referring now to Figure 4 there is shown how an at least partially loaded sail arrangement may change shape when tacked. Battens 2 are able to move from one sail panel to the other within the envelope formed by the sail panels 5.

Referring to Figure 5 this shows a mast section 9 incorporating roller furling type devices 10A,10B which are attached to the luff edges of the sail panels 5 enabling them to be independently wound in or out. This illustration also shows a batten 1 1 with a batten stop 12 which bears against the rear edge of the mast section restraining the batten's movement into the mast. Figure 5 shows how a part 13 of the batten 1 1 sits within the mast section through an entry into the mast section 14. This batten entry point may comprise a number of holes in the mast through which each batten is inserted or may comprise a slot into which the battens are inserted. The slot type aperture may be used where it is considered desirable to alter the vertical position of the batten on the mast or enable the batten to move up and down the mast for purpose of sail reefing or storage.

Referring now to Figure 6 this shows sail arrangement as described in

Figure 5 however with the roller furling device 10A let out and roller furling device 10B wound in so that sail arrangement is able to adopt the curved profile shown. Figure 10 shows a sail arrangement as shown in Figures 5 & 6 where operation levers 17 & 18 are connected to each of the roller furling devices. These levers 17 & 18 may be held with each end roughly in line with the centre line 1 9 of the craft on which the wing sail is being used.

As the mast rotates (arrow 22) from one tack to the other it will cause the roller furling devices to let in and let out the sail fabric on opposed sides. The roller furling levers may also be used to further tension the sail fabric by additional rotation 20 of one of these levers in this case 18 to position 21 .

Referring now to Figures 1 1 & 12 these show a mast incorporating two side by side mast sections 23 & 24. These sections 23 & 24 are capable of being moved apart from one another as shown in Figure 12 so that the overall depth of the mast from leading edge 25 to trailing edge 26 may be lengthened or reduced. Altering the effective depth of the mast in this way will result in a load being applied to the battens and the sail panels between which the battens are used. Many different ways may be used to move the two mast sections 23 & 24 apart in this type of sail arrangement. These include screw type levers, hydraulics, electronic actuators and pneumatic actuators. The mast sections may be moved apart from each other in a roughly parallel fashion or angled or bowed or in segments.

Figure 13 shows an example of one of the many different types of device that may be used to control the batten. In this case cordage 29 is attached to one end of the batten 27 within the mast 28 which follows a path over a bearing wheel 30 then down the mast where force may be exerted on it. Pulling the cord in the direction indicated 31 will cause the batten to move out of the mast void somewhat as indicated 32. In so doing compression load may be imparted on the batten and a sail panel curved.

Referring now to Figure 14 this shows how a lever 32 may be attached to a batten 33 near the batten's leech end, one end of the lever being attached to the sail at the leech 34. A batten stop 35 bears against mast 36 so when force is applied with cordage 37 that is attached to an other end of the batten lever 38 the lever will pull downwards (as indicated by 39) thereby increasing the effective luff-to-leech length of the batten thus imparting or increasing curvature and applying force to the sail panels thus tensioning them in a roughly horizontal direction. This tensioning can result in the creation of a wing aerofoil section similar to that shown in Figure 2.

Referring now to Figure 15, there is shown one design which comprises a teardrop section mast 40 with first and second section sail panels 41 that extend from the leech forward to, and around the front of, the mast to meet together to form a continuous sail envelope. Each of a set of battens 42 enters a rear part of the mast section at intervals along the mast length so that part of each batten sits within the mast section and extends aft towards the sail leech 43 whereat they bear upon or are attached to the sail envelope.

The battens have a projection which bears against the outer surface of the mast acting as a stop situated a short distance from the end of the batten which enters the mast. Each batten is connected by hinges 44 located a short distance from the leech end of the each batten. Cordage 45 is secured close to each batten hinge 44 and extends down from the uppermost batten to the next down and so forth until it reaches the foot of the sail. The cordage may be pulled to apply force to it to adjust the angle of each batten so that they move from a relaxed angled position to a straighter more loaded form (thereby extending the effective luff-to-leech distance) such that the battens curve more in a substantially lateral plane and impart a curve to the sail fabric envelope.

The sail envelope formed from the sail panels may also be tensioned vertically between head and foot of the sail so as to help maintain the shape generated by the bent batten on the sail.

The embodiment of Figure 5 is suited to larger boats and those going offshore. In this embodiment the mast has two side by side cavities that run vertically all or much of the length of the mast. These would normally cover the length at least between foot and head of the sail. They are located adjacent the leading edge of the mast and a roller reefing system is located within each.

Each roller reefing device serves one of the two sail panels that make up the wing sail envelope. These roller reefing devices can serve one or both of two principle functions. The first is to bring the sail from its fully extended form back to a fully reefed or stowed form, and the other is to selectively tension one of the sail panels so as to load the battens. The more one sail panel is wound in the greater the load placed on the battens thus producing greater depth of cord for the other sail panel.

A lever may be connected to the base of each of the roller reefing devices so as to aid control of tensioning. This can not only put one side of the sail envelope into tension but to let in and out both of the sail panels during tacking. This could be achieved by restraining the ends of each of the mast levers roughly at the centre line of the boat whilst the mast rotates relative to them to the next tack position. This causes the leeward roller reefing unit to let out and the windward one to be brought in as the mast section rotates to its sailing position (as shown in Figure 6). Each roller reefing unit will use a ratchet or locking device to allow their respective sail panels to be locked at their desired length before any rotational tack adjustment and further tensioning take place.

This design for a sail featuring two roller reef devices has a mast section, as shown in Figure 5, the trailing edge of which is substantially open so as to permit the battens incorporated in this design to be able to move up and down the mast and allow reefing or stowage. Figures 7,8 & 9 show the progression of a sail being stowed, where Figure 7 shows the rig with sails fully stowed, Figure 8 shows it partially reefed and Figure 9 shows it fully extended.

Conveniently the mast may be mounted on a craft by a mast step arrangement which allows the mast to pivot about a generally vertical mast pivot axis. For windsurfing applications the mast may pivot about three axes.

Figures 1 6 to 20 show a further arrangement including a further embodiment of batten 50 (as shown in Figure 1 6 with parts thereof in Figures 17 and 18) which is formed from two batten elements 51 , 52 that have opposite D-shaped cross-sectional profiles (See Figure 1 8) and are joined at their luff ends 53 and leech ends 54. In a relaxed state with no load applied the batten elements 51 , 52 each have opposed gentle curvatures that corresponding to the minimum curvature that is desirably imparted to a sail panel. Application of a load may increases the curvature. The batten 50 is attached to a mast 55 at the luff end 53 by means of a pivoting connector 55.

Pairs of pivoting arms 58 extend between inwardly directed faces of the batten elements. The arms of each pair are connected to each other and to the batten elements. A tension member 59 links to the pivot point of each pair of arms and runs down the mast or luff of the sail. Pulling the tension member increases the angle between the arms of each pair thus forcing the batten elements apart as shown in Figure 20. Releasing the tension member allows the batten elements to return to the relaxed configuration as shown in Figures 16 and 19.

As best seen in Figures 19 and 20 the curvature of the windward batten element will not affect the flat shape of the windward side of the aerofoil. When the arrangement is tacked the windward batten element will become the leeward batten element and will engage with the sail panel as the other batten element disengages from the opposed panel. This embodiment also shows a sail envelope tensioner at the leech end 54 of the batten. This comprises a lever arm 60 connected at first point 61 to the sail leech and at second point 62 to the batten leech end such that control of the force applied by the tensioner 63 can alter the tension in the sail envelope 57. This may also alter the axial compressive load on the batten and so aid in control of the curvature. The tensioner 63 may be linked to a sheeting arrangement (not shown) such that release and re-tensioning of the sheet during tacking can be linked to control of the sail envelope tension during that manoeuver.

Figures 21 and 22 show a yet further embodiment of sail arrangement which uses an inflatable batten. In this embodiment a mast 65 and an inflatable batten 66 are contained in a sail envelope 57. The batten 66 has three chambers that may be inflated. Figure 21 shows only the outer chambers 67 and 68 inflated, with the outer surface of the outer chamber 67 imparting the minimum desired curvature to one side of the sail envelope 57. Inflation of a middle chamber 69 as shown in Figure 22 applies a lateral load and forces the outer chambers apart thus increasing the curvature of the profile.

A still further arrangement is shown in Figures 23-25. In this embodiment the effective length (in a generally horizontal direction as viewed in Fig 23) of the battens is adjusted by altering the angle of the battens 1 00 within a plane that includes the mast 101 . The location of the leech end of each batten 100 along the leech edge 102 of the sail panels 103 is set, but the vertical location of the mast end thereof may be adjusted. This changes the angle of the battens and thus their effective horizontal length thereof. The mast end of each batten is connected to a wheeled-car 1 05 (best shown in Figure 25) with wheels 107 that will run up and down the mast in a track 106. Each car is linked to the adjacent ones by a flexible line 1 08 which allows them to be adjusted together. The car 105 permits rotation of the batten 1 00 about a pivot 109. A mast end section 1 10 of the batten 100 extends through and into a curved element 1 1 1 that is connected to the pivot 109. This permits the mast end section 1 10 to move laterally as the batten adopts a curved profile. That ensures the best aerofoil curve is imparted to the sail panels.

The sail panels are joined along the line 1 1 2 which may represent a stitching or gluing line. This is not straight along the trailing edge of each panel but is in that vicinity and extends to that edge at each batten 1 00. In this embodiment the edges are not joined at the batten thereby forming an opening 1 14 large enough for the batten to extend therethrough. The leech end of a batten 100 that is extending through that opening 1 14 is shown in Figure 24. In this version a webbing strap 1 16 is attached (not visible) to one sail panel and passes through an eye 1 18 in the batten (or simply around the end thereof) and back to a buckle 120 on the other sail panel. This permits adjustment in the amount by which the batten end extends beyond the leech edge. This is useful in adjusting the sail set, batten tension and for reefing. A mechanism for more dynamic and/or remote adjustment of the leech edge position along the batten may be provided.

A variety of batten designs have been discussed herein. It would be possible for a sail with a plurality of battens to have all the same type of batten or any mixture of more than one different type.