GB2405628A

GB2405628A - High efficiency aerofoil sail

Info

Publication number: GB2405628A
Application number: GB0419437A
Authority: GB
Inventors: Guy Nigel Mercer
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-09-02
Filing date: 2004-09-02
Publication date: 2005-03-09
Also published as: GB0419437D0; GB0320569D0

Abstract

A sail (6, Fig 1) is mountable in a generally vertical plane to a mast (5) of a sailing vessel (1, Fig 1). The sail comprises several profiled former bodies (14) with convexly curved sides (23, 24), each former body (14) having an elongate batten (10) pivotably mounted thereto within a divergent recess (18). A skin (20,21) of sailcloth extends from a seam (22) fixed to each batten (10) at a point remote from the respective former body (14), around the curved sides (23, 24) and leading edge of the former bodies (14) and back to the seam (22). When the batten (10) is pivoted towards or contacts either side wall (19) of the recess (18), the skin (20, 21) of the sail adopts an aerofoil section profile that is concave towards a corresponding face of the sail. A single-skinned portion (11) of the sail, also mounted to the battens (10), extends outwardly from a trailing edge of the double-skinned aerofoil portion (12). In a preferred embodiment, the sail (60, Fig 13) extends both fore and aft of the mast (5). The sailing vessel may be a catamaran, and its mast (5) and hull or hulls (2, Fig 1) may be dismantleable for transportation or storage.

Description

HIGH EFFICIENCY SAIL

The present invention relates to a sail for use with fore-and-aft rigged sailing vessels. More particularly but not exclusively, it relates to a sail having an aerofoil section and which can conveniently be stowed in a compact condition, for example for off-water transportation. It also relates to a rig for a sailing vessel provided with such a sail and with a mast dismantleable into sections for storage and transportation.

Many recreational sailing vessels use what is known as a fore-and-aft rig. A generally triangular mainsail extends aft from a single mast. In larger and more elaborate craft, further sails, such as foresails, jibsails, spinnakers and the like, are rigged forward of the mast, but most smaller vessels rely on a single mainsail.

A conventional yacht, catamaran or dinghy can be kept permanently at a mooring, but this may not be convenient or economical. It is known to unstop the mast of a dinghy or the like, lay it generally horizontally fore-and-aft on the hull and tow the combination behind a motor vehicle, to and from the body of water on which it is to be sailed. However, this makes for an unwieldy tow, and requires considerable space for storage off the water. There is hence considerable interest in sailing vessels that can be further dismantled for more compact transportation and storage.

Our copending tJK Application No. 0222329.5 addresses the issue of producing a catamaran hull which can conveniently be dismantled and packed in a form sufficiently compact to be carried on a motor vehicle roof rack, for example. IIowever, the problem remains of conveniently transporting and storing a mast, whether for a catamaran or a monohull vessel.

Attempts have been made to produce sectional masts, storable as separate sections which are then mounted end-to-end to form a longer mast in use. Many problems have been encountered with such masts. they are not as stable as one-piece masts, and so require additional stays to hold each section upright and in alignment. This can significantly complicate the rigging of a vessel fitted with such a mast. It is also difficult to combine a sectional mast with conventional arrangements for raising and lowering a mainsail rigged thereto.

A conventional mainsail rig comprises a boom, pivotably mounted at one end to the mast and extending generally aft therefrom. A lower edge of the mainsail is mounted to this boom. A conventional boom is rigid and relatively heavy, to withstand the stresses produced by the sail in high winds. This reduces the transportability ofthe boom and hence the vessel.

As a general rule, the boom is mounted to extend generally level with the heads and upper bodies of crew of the vessel. When the vessel is manoeuvring, particularly when tacking, the boom and sail may swing rapidly from side to side. It is not unknown for an inattentive crew member to be hit by a swinging boom, which has sufficient momentum to cause serious injury, and/or knock out an unlucky crew member, who could even be swept overboard.

Many recreational sailors would therefore appreciate an alternative to the conventional mast, boom and mainsail rig.

A vessel with a conventional sail arrangement is propelled by momentum transfer from air flow diverted by the sail. The sail, constrained at its forward and lower edges by the mast and boom, bellies out in the wind into a curve, the concave side of which thus diverts the airflow. However, since the mast and boom are substantially rigid, the curvature of the sail is mainly limited by the extensibility (and strength) of the sail itself. It would therefore be of benefit if a sail or rig could be provided that allows control over the curvature of the sail, for example controllably producing a greater curvature to catch lighter breezes.

The propulsion provided by a sail would also be increased if it had an aerofoil profile, similar to that of the wing of an aircraft, but oriented so that the Bernoulli effect leads to a generally horizontally- directed force, rather than vertical lift. Aerofoil sails are known, but they are very elaborate, the aerofoil shape being defined by an array of curved battens extending along each surface of the aerofoil, with sailcloth, (which term will be used generally herein to describe any material, natural such as canvas or non-natural such as plastics sheeting) , stretched across each array of battens - similar to the wing structure of early aircraft.

However, unlike an aircraft wing, it is desirable for a sail to have a reversible curvature, depending on the angle of the wind, and this is very difficult to arrange for the structure described. Such sails are also difficult or impossible to raise and lower like a conventional sail. It would therefore be desirable if a sail which can easily be raised and lowered (and stowed) could benefit from the added efficiency of an aerofoil profile while being as versatile as a conventional sail.

A particular problem for catamarans is that they can be difficult to turn, particularly when headed towards the wind, the high directional stability of the catamaran hull form being in this regard a drawback. In a conventional mainsail rig, the orientation of the sail is controlled, relative to the wind, by a line extending from an end of the boom remote to the mast to a point generally on the centreline of the vessel. While this point may be conveniently adjacent the tiller, it restricts the angles through which the sail can controllably be swung. An alternative arrangement, to allow controllable movement of the sail through a wider arc, would thus be advantageous, allowing the force of the wind on the sail to be redirected so as to aid turning of the vessel in a desired direction.

Another problem of catamarans is that although they are highly resistant to capsizing, due to their high overall beam, if they do tip over they tend to invert completely and can be very difficult to right. It would thus also be useful if a sail or rig for a catamaran, or indeed for any yacht, dinghy or the like, would also address this problem.

A type of sail which is superficially attractive because of its simplicity and robustness is the luff sail. Rather than being rigged to the mast by a conventional arrangement of halyards and the like, this has a sleeve, extending along its vertical, in use, edge, which encircles the mast completely. A standard luff sail cannot be raised and lowered like a conventional sail, however - the sleeve must be slid on and off over the tip of the mast. Instead, a luff sail is usually stowed wound around the mast, then unwound for use. This arrangement is not particularly convenient with a sectional mast, with its requirement for extra stays, partway up the mast.

Conventional fore-and-aft mainsail rigs thus have a number of drawbacks. It is hence an object of the present invention to obviate some or all of the above problems and provide a sail and/or rig which is more efficient than conventional equivalents, more convenient in use, more controllable, and/or easier to stow and transport.

According to a first aspect of the present invention, there is provided a sail mountable in a generally vertical plane to a mast of a sailing vessel, comprising at least one former body connectable to the mast and having convexly curved sides, at least one elongate member pivotably mounted to and extending from a respective former body and a double skin of sailcloth extending from a remote point of the at least one elongate member to the at least one former body passing around at least part of each convexly curved side thereof, whereby at least a zone of sail between the mast and the remote point of the at least one elongate member can assume a profile comprising an aerofoil section of shape determined by the angle of the elongate member with respect to the former body.

Preferably, said aerofoil zone extends between the or each former body and the remote point of the or each elongate member.

The or each former body may define a leading edge of said aerofoil section.

Preferably, said double skin of sailcloth extends around the mast.

Advantageously, said aerofoil zone extends substantially from a lower, in use, edge of the sail to an upper, in use, edge thereof.

The sail may be controllably reconfigurable between a hoisted disposition and a lowered disposition.

A plurality of said profiled former bodies and associated elongate members may be provided, each spaced from its neighbours along the extent of the aerofoil zone when the sail is in a hoisted disposition.

Preferably, the or each profiled former body is provided with means to restrict the extent of the pivoting motion of the respective elongate member.

Advantageously, the or each profiled former body is provided with recess means diverging from a point about which a respective elongate member is pivotably mounted, so that its pivoting motion is restricted by opposed angled walls of the recess means.

Thus, when the or each elongate member contacts a first face of the recess, the sailcloth extends around substantially the full length of the convexly curved side of the respective former body remote from the first face, thereby forming a convex low pressure zone of the aerofoil, while the sailcloth contacts only a portion of the convexly curved side adjacent the first face, thereby forming a high pressure zone of the aerofoil.

Additional means to restrict the extent of the pivoting motion of the or each elongate member may be provided.

Said additional restricting means may comprise a pair of control lines, extending through at least one profiled former body adjacent a midline of a mouth of the recess, transversely to the corresponding elongate member with one said control line disposed to either side of said elongate member.

The control lines may be selectably tautenable, thereby opposing pivoting movement of the or each member.

Thus, the aerot'oil zone of the sail may be limited to a less pronounced aerofoil cross-section than when the control lines are slack and the or each elongate member is free to pivot sufficiently t'ar as to contact a wall of the recess.

The or each former body may be directly connectable to the mast.

The or each former body may then comprise aperture means adapted to receive the mast slideably therethrough.

Alternatively, the or each elongate member may be directly connectable to the mast.

The or each elongate member may then comprise sleeve means adapted to receive the mast slideably therethrough.

Said sleeve means may comprise substantially elliptical aperture means, optionally having a major axis of the ellipse aligned with a longitudinal axis of the respective elongate member.

The mast may thus extend obliquely through the or each sleeve means, for example during hoisting or lowering of the sail.

Strap means may be provided, extending generally from an upper, in use edge of the sail to a lower, in use edge thereof, and comprising one or more loops disposed to receive the or a respective elongate member.

The strap means may extend within the aerofoil zone of the sail, optionally adjacent the or each profiled former body.

The double skin of the sailcloth in the aerofoil zone may comprise a single sheet of flexible material, mounted fixedly to the or each elongate member adjacent the remote end thereof and free to move slidingly around the convexly curved surfaces and leading edge of the or each profiled former body.

The or each profiled former body may be provided with bearing means, across which the sailcloth may move slidingly, so as to reduce friction and wear on the sailcloth.

Optionally, the sail may be provided with buoyancy means.

The buoyancy means may comprise a selectably inflatable compartment disposed adjacent an upper, in use, end thereof, preferably within the aerofoil zone, optionally forward of the mast.

In a preferred embodiment, the sail comprises a single-skinned zone, extending outwardly from adjacent the trailing edge of the aerofoil zone.

Advantageously, the or each elongate member of the aerofoil zone also extends across the single-skinned zone of the sail.

The single-skinned zone may comprise a skin mounted directly to the or each said elongate member.

The mast preferably extends through a portion of the sail intermediate between a leading edge of the aerofoil profile and a median line of the sail extending midway between said leading edge and the trailing edge of the sail.

Advantageously, the mast passes through a portion of the sail located between one eighth and three eighths of a distance measured from said leading edge back towards said trailing edge, optionally through a portion located at approximately one quarter of said distance.

A centre of pressure of the sail may be located adjacent the mast, preferably between the mast and a trailing edge of the sail.

According to a second aspect of the present invention, there is provided a waterborne vessel provided with a sail as described in the first aspect above.

Preferably, the waterborne vessel is provided with a mast comprising a plurality of sections, each separable from the others for transportation and storage.

Advantageously, the vessel is provided with a plurality of hulls, and may for example be a catamaran.

Optionally, the hull or hulls of the vessel may also be dismantleable for transportation and storage.

According to a third aspect of the present invention, there is provided a sail mountable to a mast of a sailing vessel, comprising collar means adapted to encircle the mast and stay means mounted to the collar means.

Preferably, the stay means is mountable adjacent an end or ends thereof remote from the collar means to a hull or hulls of the vessel.

Advantageously, a portion of the sail is also adapted to encircle the mast.

The collar means may then be disposed substantially within said encircling portion of the sail.

The collar means may then be provided with mounting means for the stay means, extending outwardly of the encircling portion of the sail through apertures provided therefor.

The collar means may be adapted to be suspended, in use, from the sail.

The collar means may be suspended from one or more suspension members, each mounted at an end thereof remote from the collar means to an attachment point on the sail which is higher, in use, than the collar means.

The sail is preferably adapted to be hoistable up and down the mast with the collar means sliding therealong.

The sail may be provided with a plurality of said collar means, each with stay means mounted thereto.

The sail may comprise a sail as described in the first aspect above.

According to a fourth aspect of the present invention, there is provided a vessel provided with a sail as described in the third aspect above.

Preferably, the vessel is provided with a mast comprising a plurality of sections, separable each from the others for transportation and storage.

A remainder of the vessel may also be dismantleable for transportation and storage.

Advantageously, main stay means are provided extending from adjacent a masthead of the vessel to a hull or hulls thereof.

According to a fifth aspect of the present invention, there is provided a sail, mountable to a mast of a sailing vessel, comprising a tensioning member mounted to extend across the sail substantially between two generally opposite edges thereof, and means controllably to lengthen and shorten said tensioning member, wherein the sail is adapted to alter its degree of curvature in response to such lengthening and shortening.

Preterably, the sail comprises at least one elongate resiliently flexible reinforcing member, extending substantially between said edges.

Advantageously, the sail comprises two said tensioning members, one extending across each opposite face of the sail.

The or each tensioning member may be mounted to one said reinforcing member, optionally adjacent each end thereof.

Shortening of the tensioning member will then draw said ends of the reinforcing member one towards the other, urging the reinforcing member to adopt a more sharply curved conformation, to which the sail will also conform.

The sail may optionally comprise a sail as described in the first aspect above.

According to a sixth aspect of the present invention, there is provided a sailing vessel comprising hull means, mast means and sail means extending away from the mast means, wherein means are provided to control an orientation of the sail means relative to the hull means, said orientation control means comprising control line means extending between a first mounting point on the sail means remote from the mast means and a second mounting point on the hull means adjacent a side thereof.

Preferably, the orientation control means comprises control line means extending between said first mounting point on the sail means and two second mounting points on the hull means, one adjacent each side thereof.

Advantageously, the or each second mounting point on the hull means is located generally level with the mast means.

The first mounting point on the sail means may be located intermediately between a first edge of the said means adjacent the mast means and a second edge thereof remote from the first, optionally generally half-way therebetween.

The sail may comprise or be mounted to a generally horizontally-extending reinforcing member, and the control line means may be mounted thereto.

According to a seventh aspect of the present invention, there is provided a sailing vessel comprising any one of the sails or rigs described above, or any combination thereof.

Embodiments of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a schematic elevation of a first sail and rigging embodying the present invention, mounted to a sailing vessel; Figure 2 is a cross-section of an aerofoil portion of the sail shown in Figure 1, taken along the line 11-11; Figure 3 is an enlarged crosssection of a mast mounting body of the aerofoil portion shown in Figure 2; Figure 4 is a perspective view of the mast mounting body shown in Figure 3, sectioned longitudinally; Figure 5A and 5B show, schematically, the principles of operation of a conventional sail and a sail with an aerofoil profile, respectively; Figure 6A and 6B show, in horizontal schematic cross-section, a sail embodying the invention, rigged to adjust its camber, in two alternative conformations; Figure 7 show, in schematic plan view, a conventional rig for controlling the orientation of a sail; Figure 8 shows, in schematic plan view, a rig embodying the present invention for controlling the orientation of a sail; Figure 9 is a scrap view of part of a sail and mast provided with a stay arrangement embodying the present invention; Figure 10 is an exploded isometric view of a stay collar isolated *om the stay arrangement shown in Figure 9; Figure 11 is an elevation of a batten-connecting strap usable with the sail shown in Figure 1; Figure 12 is a scrap perspective view of a loop of the strap shown in Figure 11, together with two alternative batten profiles; Figure 13 is a schematic elevation of a second sail and rigging embodying the present invention, mounted to a sailing vessel; Figure 14 is an exploded perspective view of a mast mounting body of the sail shown in Figure 13; and Figure 15 is a schematic plan view ofthe mast mounting body shown in Figure 14, in position on a mast.

Referring now to the Figures, and to Figure I in particular, a sailing vessel 1 comprises a hull 2, extending from bow 3 to stern 4, provided with a single mast 5 extending upwardly therefrom. A single first mainsail 6 is mounted to the mast 5.

For simplicity, the mast 5 is in Figure 1 represented only by its longitudinal axis. In practice, it will comprise an elongate tube of carbon fibre or of metal (for example aluminium alloy), or (as here) a plurality of tubular sections of carbon fibre or the like assembled endto-end by means of connectors which permit the separation of the sections for storage and transportation. Since the vessel 1 shown has a sectional mast 5, it is provided with not only a conventional set of stays 7, extending between the masthead 8 of the mast 5 and the hull 2, but also a set of intermediate stays 9 which extend from the hull 2 to an intermediate portion of the mast 5. The exact interconnection of the mast 5, sail 6 and intermediate stays 9 is shown in more detail in Figures 9 and 10 below.

While the above description is phrased in terms of a monohull vessel 1, it is equally applicable to vessels 1 with a catamaran or even trimaran hull form with appropriate adjustments to the rigging, such as providing stays 7. 9 running to the bow 3 of each hull 2 of a multi-hulled vessel.

The sail 6 does not have a conventional single boom extending along its lower edge. Instead, it is provided with a series of elongate battens 10, each extending generally horizontally across the sail 6 from a pivotable mounting connected to the mast 5 (shown in detail below).

Each batten 10 is substantially slimmer and lighter than a conventional boom, since any stresses will be shared between many of them. In a preferred embodiment, some or each of the battens 10 have a degree of flexibility in a generally horizontal plane.

The sail 6 is divided into two portions. An outer portion 11 remote from the mast 5 comprises a single thickness of conventional sailcloth or the like. An inner portion 12 has two surfaces of sailcloth, etc which define an aerofoil profile between them, encircling the mast 5.

An inflatable chamber 13 is provided between the two surfaces of the aerofoil portion 12 adjacent the masthead 8. Should the vessel 1 capsize, the inflatable chamber 13 will provide buoyancy, preventing the vessel I from completely turning turtle, even when it has a catamaran hull form. It will be far easier to right a vessel I from a position in which the mast is held roughly horizontally, not much below the surface of the water, by the chamber 13 than from a position in which the vessel I is completely inverted.

Other features of the rigging shown in Figure I will be described in detail below.

Figure 2 shows the aerofoil portion 12 of the sail 6 in more detail. A mast mounting body 14 is mounted around the mast 5 so that it may rotate freely in a horizontal plane about the longitudinal axis of the mast 5. The mounting body 14 is free to slide up and down the mast 5.

Each batten 10 is connected to a corresponding mounting body 14. An end of the batten 10 proximal to the mast 5 is provided with a cylindrical bearing 16, which is free to turn within a correspondingly shaped socket 17. The socket 17 is disposed at an inner end of a generally wedge-shaped recess 18 in the mounting body 14, a mouth of which is oriented away from the mast 5. The batten 10 may thus pivot about the bearing 16 between two limiting dispositions, in which it is in contact with one or the other of the two divergent walls 19 of the recess 18.

The aerofoil portion 12 of the sail 6 has two surfaces 20, 21, formed from a single sheet of a sailcloth, extending from a seam 22 at an outer edge of the aerofoil portion 12 remote from the mast 5, around an outside of the mounting body 14 and back to the seam 22. The outer portion 11 of the sail 6 comprises a single layer of sailcloth. The outer portion 11 of the sail 6 and the seam 22 are mounted fixedly to the batten 10, maintaining each surface 20, 21 of the aerofoil portion 12 in tension. The sheet forming the two surfaces 20, 21 is free to slide across the outside of the mounting body 14. A roller bearing 15 is provided over which an inner face of the sheet of sailcloth may slide, thus reducing friction between the sailcloth and the leading edge of the mounting body. This also reduces wear on the sailcloth. If desired, an area of the sheet of sailcloth which is contactable by the mounting body may be reinforced with an extra layer of sailcloth, and/or it may be lined with a layer of friction-reducing material.

Thus, when the batten 10 is disposed against one angled wall 19 of the recess 18, as shown, the sail surface 20 which is further away, pro rem, from the batten 10 extends along a whole of a corresponding curved face 23 of the mounting body 14, and thence straight to the seam 22. However, the sail surface 21 which is closer, pro lem, to the batten 10 extends along only a part of a corresponding curved face 24 of the mounting body 14 before leaving it tangentially to extend to the seam 22. The two surfaces 20, 21 thus define an aerofoil profile, airflow over which produces a force directed generally towards the surface 20.

The mounting body 14 is bilaterally symmetrical, such that when the batten 10 is in contact with the other angled wall 19 of the recess 1 8, the aerofoil portion 12 adopts a mirror-image conformation to that shown, in which sail surface 21 is now longer and more convex than sail surface 20, and airflow over the aerofoil portion 12 leads to a force directed towards surface 21. The sail 6 thus has an aerofoil portion 12 which can be switched between aerofoil profiles oriented to either side. Conventional aerofoils, defined by battens extending along each surface thereof, are restricted to a single orientation.

Optionally, an additional degree of control can be exerted by means of a pair of control lines 25, each extending generally parallelly to the mast 5 and passing through a respective aperture 26 in each mounting body 14, adjacent the mouth of the wedge-shaped recess 18.

Where the control lines 25 are in use, the batten 10 is disposed to extend between them. If the control lines 25 are slackened, the batten 10 is free to pivot from side to side within the recess 18. However, if the control lines 25 are tautened, they will oppose movement of the batten 10 towards the angled walls 19 of the recess 18. The profile of the aerofoil portion 12 of the sail 6 thus becomes less pronounced than when the control lines 25 are slack. In principle, with sufficient tension in the control lines 25, the aerofoil portion 12 could be held in a bilaterally symmetrical profile, eliminating the forces to one side or the other that it This would be of benefit in high winds, in which a sail 6 augmented by an aerofoil portion 12 would be more than is needed to propel the vessel 1 sufficiently rapidly. Indeed, in high winds, there is a risk that a highly efficient sail 6 could lead to dangerously excessive forces on the sail 6 and mast 5. The arrangement shown in effect allows the aerofoil portion 12 of the sail 6 to be discounted when not required, allowing the sail 6 to behave as a conventional sail.

It is also envisaged that a plurality of pairs of control lines 25 could be employed, each pair being connected to only one or only some of the mounting bodies 14 of the sail 6. Thus, the profile of the aerofoil portion 12 could be adjusted independently at different zones thereof, allowing finer control over the performance of the sail 6.

Figure 4 shows the mounting body 14 of Figures 2 and 3 sectioned longitudinally, to reveal its structure. The mounting body 14 comprises a strong, low density metal, such as an aluminium alloy, or preferably a strong, substantially rigid plastics material, either a thermoplastics material or a thermosetting resin or the like. The mounting body 14 can be forged, injection moulded, blow moulded or otherwise formed as is appropriate for the raw materials used. Upper and lower (in use) faces of the body 14 are provided with indentations 27, to reduce the weight of the body 14 and to define the socket 17 and angled wall 19 of the wedge-shaped recess 18.

It may be convenient to form the body 14 as substantially identical upper and lower (in use) halves, joined one to the other along a substantially horizontal seam 28, for example with adhesive. In this case, a floor ofeach indentation 27 may conveniently be mounted directly to its counterpart.

In the body 14 shown, elongate slots 26a are provided to receive the pair of control lines 25.

A plug may be inserted generally at a midpoint of each slot 26a to divide it into two apertures 26 as in Figure 3, or the slots 26a may be used undivided with one control line 25 passing through each end of each slot 26a.

Note: the roller bearing 15 is shown schematically only. The tension in the sailcloth of the aerofoil portion 12 urges it very firmly into contact with this region of the body 14. Thus, in the absence of such a bearing 15, friction between the sailcloth and the body 14 would be very high, wearing out the sailcloth and reducing the responsiveness of the sail 6.

The sail 6 can be raised and lowered using a conventional arrangement of halliards, blocks and the like. Each mounting body 14 is *ee to slide up and down the mast 5 as the sail 6 is raised and lowered. When the sail 6 is fully lowered, the mounting bodies 14 and the battens will be stacked each substantially in contact with its neighbours, with the sailcloth or the like of the sail 6 folded to one side or concertinaed therebetween.

the sail 6 can be removed from the mast 5 and stowed for transport, etc. as a compact elongate bundle with the battens 10 each extending substantially parallelly to the others.

Optionally, a bag or the like can be provided to hold the lowered or stowed sail 6.

Turning now to Figures I I and 12, the raising and lowering of the sail 6 may be eased by the provision of an elongate strap 49, of stout webbing or the like, which extends from an upper, in use, edge of the sail 6 to a lower edge thereof, within the aerofoil section 12. The strap 49 extends adjacent the recess 18 of each mounting body, and is provided with a series of loops 5(), each of which receives a respective batten 10 of the sail 6 therethrough. The strap 49 is mounted at each end to the sail 6, either at a single mounting point 51, or by means of a bifurcated terminal section 52 provided with two mounting points 51, as is convenient.

Thus, as the sail 6 is raised, the strap 49 draws the battens 10 upwardly, and it also holds them in a correct disposition once the sail 6 is fully raised. Each mounting body 14 will be drawn up the mast 5, following its respective batten 10.

Figure 12 shows an individual loop 50, with sections of two alternative battens 10a, 10b of different profiles aligned therewith. A batten with a simple rectangular profile lea may be used, or a batten with a waisted profile lOb may be preferred, the latter giving a different balance of strength, weight and flexibility.

The strap 49, by connecting all of the battens 10, may also serve to smoothen and align the pivoting movements of the battens 10, each with the others.

Figures 5A and 5B contrast the principles of operation of a conventional sail 29 and a sail 6 with an aerofoil profile, respectively. In each case, the sail 29, 6 is mounted to the mast 5 of a vessel travelling along a course marked by dashed arrow 30. The vessel is running close to the wind, which is on the port bow of the vessel, as shown by arrow 31.

For a conventional sail 29, the wind 31 bellies the sail 29 so that it adopts a conformation that is concave towards the wind 31. The airflow 32 incident on this concave face of the sail 29 is thus diverted as shown. This transfers momentum to the sail 29, resulting in a force 33 on the sail 29 which is transmitted via the mast 5 to the vessel. A component of the force 33 parallel to the course 30 of the vessel propels it forwards.

For a sail 6 with an aerofoil profile, the airflow 32 incident on its concave face is diverted as described above. IIowever, the airflow 34 passing across its convex face has an additional effect. The convex face is longer than the concave face, unlike a conventional single- thickness sail 29, and so the airflow 34 over the convex face must flow faster than the airflow 32 over the concave face. By the Bernouilli effect, the air pressure over the convex face is therefore lowered, relative to that over the concave face, and an additional force is created directed towards the convex face. The overall force 35 exerted on the sail 6 is hence greater than the force 33 exerted on the conventional sail 29.

Clearly, for winds on the starboard bow, an aerofoil of mirror-image curvature is required.

An aerofoil of known form, with battens fixedly defining each surface, is thus not suitable, while the sail 6 of the present invention is free to change its conformation as the wind takes it.

The efficiency of a sail can also be improved by controlling how concave it is; the greater the camber of the sail, the greater the angle through which the airflow 32 incident on its concave face is diverted and so the greater the momentum transferred to the sail. A conventional sail 29 has a limited amount of slack built in, and the sailcloth, from which it is made is slightly extensible. Thus, as the wind increases, the sail 29 bellies out further and becomes more efficient. Unfortunately, in high winds, a highly efficient sail is not required and may even result in forces sufficient to tear the sail 29 or damage the mast 5 and its stays, 7, 9. What is required is a sail which is highly efficient at lower wind speeds.

The sail 6 shown in Figures 6A and 6B is provided with a tensioning line 36, extending from adjacent the mast 5 to a tensioning device 37 mounted to an outer edge of the sail 6 remote from the mast 5. The tensioning device 37 is also mounted to a tip of a batten 10, which is resiliently flexible in at least a generally horizontal plane.

Thus, if the tensioning device 37 is operated to shorten the tensioning line 36, the batten 10 will bow out, as shown in Figure 6B, and the camber of the sail 6 as a whole will increase, allowing it to catch light winds more efficiently.

A corresponding second tensioning line (not shown) is provided extending from the tensioning device 37 to a point adjacent the mast on an opposite side of the sail 6 to the line 36. This is left slack in the conformation shown, but may be shortened instead of the line 36, to impose or increase a curve on the sail 6 in the opposite sense to that shown.

While the sail 6 shown has an aerofoil portion 12, this arrangement is equally applicable to sails having a conventional single-skinned form, as long as they are provided with flexible battens 10 or the like, and not the substantially rigid boom of a conventional mainsail.

A further problem found with conventional rigging of a yacht, etc. particularly one with a catamaran hull, is shown in Figure 7. (This problem can occur both with a conventional sail 29 fitted and with an improved sail 6 as described above). As in Figures 5A and 5B, a vessel is following a course 30 with the wind 31 on the port bow. It may be desired to alter course, to turn the vessel into the wind and beyond, so that the wind 31 is on the starboard bow. This can be difficult to achieve, particularly for a catamaran vessel, which has great directional stability.

In a conventional mainsail rig, the orientation of the sail 29 is controlled by a line 38 extending from a tip of the boom (not shown for clarity) to a winch 39, or the like, mounted on a centreline of the vessel, conveniently adjacent a tiller. (For a sail 6, such as shown in Figure 1, the line 38 would instead extend from a tip of a lowermost batten 10). This arrangement only allows the sail 29 to be drawn towards the centreline or to be let out until it extends parallel to the wind, at which point it is subject to no turning forces.

In an alternative rig, as shown in Figure 8, the line 38 is replaced or supplemented by a pair of lateral control lines 40. Each lateral control line 40 extends from a block 41, mounted adjacent a respective side of the vessel and generally level with the mast 5, to a mounting 42 at an intermediate point along a lower edge of the sail 29 (or an intermediate point along a boom, or a batten 10 of an improved sail 6, as appropriate).

The lateral control lines 40 can be used to turn the sail 29 through an arc of almost 180 , between extending generally over the starboard beam and extending generally over the port beam. The leverage exerted by the lines 40 is sufficient to move the sail 29 controllably between these extremes. In particular, the sail 29 can be drawn from a position such as that shown in Figure 7, across the wind, to a position such as that shown in Figure 8. The direction of the force 33 exerted on the sail 29 is thus substantially altered - in this case, it is redirected from (generally) to starboard to (generally) to port and will now help to turn the bows of the vessel to port, thus turning into and across the wind, and on to a course with the wind on the starboard bow.

The wide beam of a catamaran allows the blocks 41 to be mounted well away from the centreline of the vessel, and so allows even greater leverage to be exerted on the sail 29. The rig shown is thus particularly suitable for turning a catamaran that would otherwise encounter problems, as described above. l As referred to above, a sectional mast 5 may need additional intermediate stays 9. However, a stay 9 extending between the mast 5 and the hull 2 is not compatible with a sail 6 which extends around the mast 5 and must be raised and lowered.

The arrangement of Figure 9 is hence employed. A collar 43 (shown in more detail in Figure 10) encircles the mast 5 and is free to turn or to slide therealong. The collar 43 is provided with two diametrically opposed bosses 44 extending radially outwardly therefrom. Each boss 44 has an eyebolt 45 mounted thereto, through which a stay 9 is passed. The eyebolts 45 may each be formed integrally with a respective boss 44, or may be formed separately and attached thereto, as shown.

The collar 43 is mounted to the sail 6 by means of a pair of suspension straps 46 (cordage or wire may be substituted if desired). the suspension straps 46 each extend upwardly from a respective boss 44, and are each sewn at their upper, in use, end 47 to an inner face of the doubleskinned portion 12 of the sail 6. The straps 46 are thus disposed on diametrically opposite sides of the mast 5. Two windows 48 are provided through the sail 6, also on diametrically opposite sides of the mast 5, such that each eyebolt 45 extends outwardly of the sail 6. The windows 48 and collar 43 are disposed at a point on the sail 6 intermediate between two battens 10 and their corresponding mounting bodies 14.

Thus, when the sail 6 is raised and lowered, the collar 43 is constrained to slide up and down the mast 5, with the stays 9 in the eyebolts 45 following it, outside the sail 6. When the sail 6 is fully raised, the stays 9 will be taut, preventing the collar 43 from undergoing significant lateral movement. Since the collar 43 closely encircles the mast 5, additional lateral support is thus provided for the mast 5.

Suspending the collar 43 from the sail 6 as shown allows the collar 43 or the sail 6 to twist about the longitudinal axis of the mast 5, without interfering with the effectiveness of the stays 9. Thus, when the sail 6 is lowered, the mast 5 is held in position only by the mainstays 7; these will suffice for the forces likely to be imposed on a bare mast 5. When the sail 6 is raised, and the imposed forces rise (for example risking buckling of the mast 5 at the joints between sections), the intermediate stays 9 are also raised into position. Ideally, a collar 43 and respective set of intermediate stays 9 are provided to correspond to each section of the mast 5 (except for the uppermost), such that an upper portion of each section is stayed when the sail 6 is raised.

A second, preferred form of sail 60 embodying the present invention is shown in Figure 13.

As for the first sail 6 shown in Figure 1, a sailing vessel 1 comprises a hull 2 (or a plurality of hulls 2), extending from bow 3 to stern 4, and provided with a single mast 5 extending upwardly therefrom. The second sail 60 is mounted to this mast 5.

The mast 5 comprises a plurality of tubular sections of carbon fibre or of aluminium alloy or the like, assembled end to end by connectors allowing disassembly for transportation and storage. As in Figure 1, the mast 5 is provided with a conventional set of stays 7 extending between the hull or hulls 2 and the masthead 8, and a set of intermediate stays 9 extending between the hull or hulls 2 and a collar 43 that encircles an intermediate portion of the mast 5 when the sail 60 is fully raised (as shown in Figures 9 and 10).

The second sail 60 also comprises a series of elongate, generally, horizontally extending battens 10, each having a degree of flexibility in a generally horizontal plane. As for the first sail 6, the second sail 60 has an outer portion l 1, remote from the mast 5, comprising a single thickness of conventional sailcloth or the like. An inner portion 62 of the second sail 60 has two surfaces of sailcloth, etc. defining an aerofoil profile between them. However, unlike the first sail 6, in which the corresponding inner portion 12 extends generally aft from the mast 5, the inner portion 62 of the second sail 60 extends both generally forward and generally aft of the mast 5. (The mounting arrangements permitting this are shown in Figures 14 and 15).

This allows the second sail 60 to be provided with an inflatable buoyancy chamber 13 that is mounted adjacent the masthead 8 within the inner portion 62, but forward of the mast 5. This position has been found to be more convenient than immediately aft of the mast 5, as is the case for the first sail 6.

As for the first sail 6, the second sail 60 is controlled (inter alla) using a pair of lateral control lines 40 extending from blocks 41 mounted to the hull or hulls 2 to a mounting 42 at an intermediate point along a lower edge of the sail 60, aft of the mast 5.

The second sail 60 may also be provided with a hoisting strap 49 connected to each batten 10, similar to that shown in Figures 11 and 12.

l o allow the sail 60 to extend both fore and aft of the mast 5, the mounting body 14 of the first sail 6 is replaced with an arrangement as shown in Figures 14 and 15.

A profiled body 64 has two lateral curved surfaces 23, 24 corresponding to those of the mounting body 14, and a corresponding wedge-shaped recess 18. In place of the roller bearing 15, the profiled body 64 is provided with two rollers 65, rotatably mounted by a common pivot pin 66 to an upper and a lower surface, respectively, of the body 64. Each roller 65 extends slightly outwardly from the body 64, as shown more clearly in Figure 15.

An elongate cam arm 68 is pivotably mounted to the profiled body 64, in this embodiment being mounted to the same pivot pin 66 as the rollers 65. The cam arm 68 may pivot between two limiting dispositions, in contact with one or other of the two divergent walls 19 of the recess 18, as for the batten 10 shown in Figures 2 and 3. (If desired, the pivoting motion of the cam arm 68 may further be limited by one or more pairs of control lines 25, similar to those shown in Figure 3, although they are not present in this particular embodiment).

An end of the cam arm 68 remote *om the profiled body 64 is mounted to an elliptical mast sleeve 67, the cam arm 68 extending in line with the major axis of the elliptical sleeve 67. A hollow batten socket 69 extends from a side of the sleeve 67 opposite to the cam arm 68, in line therewith and with said major axis. The batten socket 69 receives an end of a batten 10, such that the cam arm 68, batten socket 69 and batten 10 behave as a single elongate body.

The elliptical sleeve 67 surrounds the mast 5. Its diameter across its minor axis is slightly greater than that of the mast 5,1eaving it free to slide or rotate with respect thereto, while its diameter across its major axis is substantially greater. Thus, when the sail 60 is being raised or lowered, the batten 10, sleeve 67, cam arm 68 and profiled body 64 may extend at an angle to the horizontal, with the mast 5 passing obliquely through the sleeve 67. If the sleeve 67 were substantially circular, there would be a risk of jamming. The sleeve 67 shown is slightly outwardly flared towards each rim. further to ease its passage obliquely up and down the mast 5.

The second sail 60 comprises a sheet of sailcloth (not shown in Figure 15 for clarity) very similar to that shown in Figures 2 and 3 for the first sail 6. The outer portion 11 of the sail 60 comprises a single sheet of sailcloth, mounted fixedly to each batten 10. The inner aerofoil portion 62 has two surfaces formed from a single sheet of sailcloth, which extends in tension from a seam 22 (not shown in Figure 15) mounted fixedly to each batten 10, towards and across a first lateral curved surface 23 of each profiled body 64, across the respective rollers 65, across a second lateral curved surface 24 and back to the seam 22. Thus, as for the first sail 6, the second sail 60 can adopt an aerofoil profile curved convexly to port or to starboard depending on the disposition of the cam arm 68, etc. within the recess 18 of the profiled body 64. As the sail 60 moves between these limiting curves, the sheet of sailcloth passes over the rotating rollers 65, which ease its passage and reduce frictional wear.

l he main advantage of the second sail 60 over the first sail 6 is due to the relative positions of the mast 5 and the centre of pressure of the sail 60. As shown in Figure 5B, the overall force 35 on the first sail 6 effectively acts at a point along a chord section substantially aft of the mast 5. Calculations indicate that this point is approximately one quarter of the distance back from a forward edge to an aft edge of the chord section of the sail 6, 60 (the precise value varies between about 22% and 29%, depending on the exact profile of the chord section). This creates a substantial leverage which, inter alla, makes it difficult to haul in the sail 6 in order to switch it from a first curved profile to a second, oppositely curved profile.

If, however, the mast 5 is positioned coincidentally with the centre of pressure of the chord section, the haul-in forces required to control the sail 60 are minimised. In practice, to achieve sufficient stability and controllability, it is preferable that the net centre of pressure remains slightly aft of the mast 5. In the rig of Figure 13, the mast 5 is close to the centre of pressure of the sail 60 adjacent the masthead 8, while it is forward thereof nearer the lower edge of the sail 60, e.g. where the lateral control lines 40 are mounted.

A further feature of the rig of the second sail 60 shown in Figure l 3 to l 5 is that, because the battens 10 are effectively pivoted at the same point as the rollers 65, it is possible with little effort to hold the sail 60 in a neutral conformation, curved neither to port nor to starboard (as shown in Figure 15), with the wind dead ahead. The first sail 6, whose the battens 10 are pivoted about a bearing 16 located substantially aft of the rollers 15, is as a result unstable in such a conformation. Any perturbation would result in the sail 6 being urged increasingly toward one limiting curve or the other (generally speaking, the first sail 6 is strongly bistable, while the second sail 6() is neutrally stable).

There are applications (for example, in racing) in which one might wish to have a strongly bistable sail and not require the ability to hold the sail "in neutral". In such cases, the arrangement shown in Figure 14 may be modified by pivoting the cam arm 68 about a point on the profiled body 64 aft of the pivot pin 66 of the rollers 65. The separation between said two pivot points would be selected to create a greater or lesser lever arm as desired.

While the invention is described above in terms of a waterborne vessel, it should be borne in mind that such sails, etc. may also be useful for sail-propelled land vehicles, such as sand- yachts.

Claims

A sail mountable in a generally vertical plane to a mast of a vessel, comprising at least one profiled former body connectable to the mast and having convexly curved sides, at least one elongate member pivotably mounted to and extending from a respective profiled former body and a double skin of sailcloth extending from a remote point of the at least one elongate member to the at least one profiled former body passing around at least part of each convexly curved side thereof, whereby at least a zone of sail between the mast and the remote point of the at least one elongate member can assume a profile comprising an aerofoil section of shape determined by the angle of the elongate member with respect to the profiled former body.
2. A sail as claimed in claim 1, wherein said aerofoil zone extends between the or each profiled former body and the remote point of its corresponding elongate member.
3. A sail as claimed in either claim I or claim 2, wherein the or each profiled former body defines a leading edge of said aerofoil section.
4. A sail as claimed in any one ol the preceding claims, wherein said double skin of sailcloth extends around the mast.
5. A sail as claimed in any one of the preceding claims, wherein said aerofoil zone extends substantially from a lower, in use, edge of the sail to an upper, in use, edge thereof.
6. A sail as claimed in any one of the preceding claims, adapted to be controllably reconfigurable between a hoisted disposition and a lowered disposition.
7. A sail as claimed in any one of the preceding claims, provided with a plurality of said profiled former bodies and associated elongate members, each spaced from its neighbours along the extent of the aerofoil zone when the sail is in a hoisted disposition.
8. A sail as claimed in any one of the preceding claims, wherein the or each profiled former body is provided with means to restrict the extent of the pivoting motion of the respective elongate member.
9. A sail as claimed in claim 8, wherein the or each profiled former body is provided with recess means diverging from a point about which a respective elongate member is pivotably mounted, so that its pivoting motion is restricted by opposed angled walls of the recess means.
10. A sail as claimed in claim 9, wherein, in a conformation in which the or each elongate member contacts a first face of the recess, the sailcloth extends around substantially the full length of the convexly curved side of the respective former body remote from the first face, thereby forming a convex low pressure zone of the aerofoil, while the sailcloth contacts only a portion of the convexly curved side adjacent the first face, thereby forming a high pressure zone of the aerofoil.
11. A sail as claimed in any one of claims 8 to 10, provided with additional means to restrict the extent of the pivoting motion of the or each elongate member.
12. A sail as claimed in claim 1 1, wherein said additional restricting means comprises a pair of control lines, extending through the at least one profiled former body adjacent a midline of a mouth of the recess, transversely to the corresponding elongate member with one said control line disposed to either side of said elongate member.
13. A sail as claimed in any one of the preceding claims, wherein the or each former body is directly connectable to the mast.
14. A sail as claimed in claim 14, wherein the or each former body comprises aperture means adapted to receive the mast slideably therethrough.
15. A sail as claimed in any one of claims I to 12, wherein the or each elongate member is directly connectable to the mast.
16. A sail as claimed in claim 15, wherein the or each elongate member comprises sleeve means adapted to receive the mast slideably therethrough.
17. A sail as claimed in claim 16, wherein said sleeve means comprises substantially elliptical aperture means, optionally having a major axis of the ellipse aligned with a longitudinal axis of the respective elongate member, so adapted that the mast may extend obliquely through the or each sleeve means, for example during hoisting or lowering of the sail.
18. A sail as claimed in any one of the preceding claims, provided with strap means extending generally from an upper, in use edge of the sail to a lower, in use edge thereof, and comprising one or more loops disposed to receive the or a respective elongate member.
19. A sail as claimed in claim 18, wherein the strap means extends within the aerofoil zone of the sail, optionally adjacent the or each profiled former body.
20. A sail as claimed in any one of the preceding claims, wherein the double skin of the sailcloth in the aerofoil zone comprises a single sheet of flexible material, mounted fixedly to the or each elongate member adjacent the remote end thereof and free to move slidingly around the convexly curved surfaces and leading edge of the or each profiled former body.
21. A sail as claimed in claim 20, wherein the or each profiled former body is provided with bearing means, across which the sailcloth may move slidingly, so as to reduce friction and wear on the sailcloth.
22. A sail as claimed in any one of the preceding claims, provided with buoyancy means.
23. A sail as claimed in claim 22, wherein the buoyancy means comprises a selectably inflatable compartment disposed adjacent an upper, in use, end of the sail, preferably within the aerofoil zone, optionally forward of the mast.
24. A sail as claimed in any one of the preceding claims, comprising a single-skinned zone extending outwardly from adjacent the trailing edge of the aerofoil zone.
25. A sail as claimed in claim 24, wherein the or each elongate member of the aerofoil zone also extends across the single-skinned zone of the sail, which comprises a skin mounted directly to the or each said elongate member.
26. A sail as claimed in any one of the preceding claims, wherein the mast extends through a portion of the sail intermediate between a leading edge of the aerofoil profile and a median line of the sail that extends midway between said leading edge and the trailing edge of the sail.
27. A sail as claimed in claim 26, wherein the mast passes through a portion of the sail located between one eighth and three eighths of a distance measured from said leading edge back towards said trailing edge, optionally through a portion located at approximately one quarter of said distance.
28. A sail as claimed in any one of the preceding claims, wherein a centre of pressure of the sail is located adjacent the mast, preferably between the mast and a trailing edge of the sail.
29. A sail substantially as disclosed herein with reference to the figures of the accompanying drawings.
30. A waterborne vessel provided with a sail as claimed in any one of the above claims.
31. A waterborne vessel as claimed in claim 30, provided with a mast comprising a plurality of sections, each separable from the others for transportation and storage.
32. A vessel as claimed in either claim 30 or claim 31, provided with a plurality of hulls, for example comprising a catamaran.
33. A vessel as claimed in any one of claims 30 to 32, wherein the hull or hulls of the vessel are dismantleable for transportation and storage.
34. A waterborne vessel as disclosed herein with reference to the figures of the accompanying drawings.
35. A sail mountable to a mast of a sailing vessel, comprising collar means adapted to encircle the mast and stay means mounted to the collar means.
36. A sail as claimed in claim 35, wherein the stay means is mountable adjacent an end or ends thereof remote from the collar means to a hull or hulls of the vessel. ;
37. A sail as claimed in either claim 35 or claim 36, wherein a portion of the sail is adapted to encircle the mast, and the collar means is disposed substantially within said encircling portion of the sail.
38. A sail as claimed in claim 37, wherein the collar means is provided with mounting means for the stay means, extending outwardly of the encircling portion of the sail through apertures provided therefor.
39. A sail as claimed in any one of claims 35 to 38, wherein the collar means is adapted to be suspended, in use, from the sail.
40. A sail as claimed in claim 39, wherein the collar means is suspended from one or more suspension members, each mounted at an end thereof remote from the collar means to an attachment point on the sail which is higher, in use, than the collar means.
41. A sail as claimed in any one of claims 35 to 40, adapted to be hoistable up and down the mast with the collar means sliding therealong.
42. A sail as claimed in any one of claims 35 to 41, provided with a plurality of said collar means, each with stay means mounted thereto.
43. A sail as claimed in any one of claims 35 to 42, comprising a sail as claimed in any one of claims I to 29.
44. A vessel provided with a sail as claimed in any one of claims 35 to 43.
45. A vessel as claimed in claim 44, provided with a mast comprising a plurality of sections, separable each from the others for transportation and storage.
46. A vessel as claimed in claim 45, a remainder of which is dismantleable for transportation and storage.
47. A sail, mountable to a mast of a sailing vessel, comprising a tensioning member mounted to extend across the sail substantially between two generally opposite edges thereof, and means controllably to lengthen and shorten said tensioning member, wherein the sail is adapted to alter its degree of curvature in response to such lengthening and shortening.
48. A sail as claimed in claim 47, comprising at least one elongate resiliently flexible reinforcing member, extending substantially between said edges.
49. A sail as claimed in either claim 47 or claim 48, comprising two said tensioning members, one extending across each opposite face of the sail.
50. A sail as claimed in any one of claims 47 to 49, wherein the or each tensioning member is mounted to one said reinforcing member, optionally adjacent each end thereof.
51. A sail as claimed in any one of claims 47 to 50, comprising a sail as claimed in any one of claims I to 29.
52. A sailing vessel comprising hull means, mast means and sail means extending away from the mast means, wherein means are provided to control an orientation of the sail means relative to the hull means, said orientation control means comprising control line means extending between a first mounting point on the sail means remote from the mast means and a second mounting point on the hull means adjacent a side thereof.
53. A sailing vessel as claimed in claim 52, wherein the orientation control means comprises control line means extending between said first mounting point on the sail means and two second mounting points on the hull means, one adjacent each side thereof.
54. A sailing vessel as claimed in claim 53, wherein the or each second mounting point on the hull means is located generally level with the mast means.
55. A sailing vessel as claimed in either claim 53 or claim 54, wherein the first mounting point on the sail means is located intermediately between a first edge of the said means adjacent the mast means and a second edge thereof remote from the first, optionally generally half-way therebetween.
56. A sailing vessel as claimed in any one of claims 53 to 55, wherein the sail comprises or is mounted to a generally horizontally-extending reinforcing member, and the control line means is mounted thereto.