WO1996011840A1

WO1996011840A1 - High speed sailing device

Info

Publication number: WO1996011840A1
Application number: PCT/NL1994/000251
Authority: WO
Inventors: Thomas Walburgis Bakker; Tjerk Bartele Bakker
Original assignee: Thomas Walburgis Bakker; Tjerk Bartele Bakker
Priority date: 1994-10-12
Filing date: 1994-10-12
Publication date: 1996-04-25
Also published as: DE69419783D1; EP0784563B1; EP0784563A1; AU1078795A

Abstract

A sailing device comprising a hull structure (1), a fin structure (2) and a sail system (3). The sail system (3) is arranged to be trimmed with its foot portion (4) to leeward of its upper portion (5) and for generating a wind resultant force including an upward lift component. The fin structure (2) is adapted for generating a lift having a downward component. During sailing in stronger winds, the downward component of the lift generated by the fin structure opposes the upward lift component of the wind resultant force, enabling to carry sails generating an upward lift component larger than the gravity forces exerted onto the device, without the device being lifted out of the water. Thus a substantially improved driving force to water displacement ratio can be achieved, so in principle higher speeds can be achieved than with known sailing device.

Description

Title: High speed sailing device

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a sailing device comprising a hull structure, a fin structure and a sail system. The sail system is arranged to be trimmed with its foot portion to leeward of its upper portion and for generating a wind resultant force including an upward lift.

Such a sailing device in form of a sailing craft is described in International Patent Application WO86/07325. Compared with a conventional sailing crafts of which the sails are maintained in a generally vertical orientation or even lean to leeward, this sailing craft can in principle carry more sail at a given wind velocity, because the lift component of the wind resultant force generated by the sail is operative along a line (vector) to leeward of the centre of gravity of the device and therefore counteracts the heeling moment generated by the combination of the lateral components of the wind resultant force and the water resistance. The described sailing craft is a proa comprising two rudders at opposite ends of an outrigger, each of the rudders being provided with fins for generating hydrodynamic upward lift.

Another example of a sailing craft which can carry more sail than a comparable conventional sailing craft is described in United States Patent 3,762,353. This sailing craft is provided with an outrigger carrying a downward pulley hydrofoil. In use, the outrigger projects to windward and therefore counteracts the sail heeling moment. However, the downward lift generated by the hydrofoil pulls the craft into the water thereby increasing the water resistance.

It is an object of the invention to provide a sailing device in which the ratio between driving forces and water displacement is improved, so that, in principle, an increased speed potential is obtained.

SUMMARY OF THE INVENTION

According to the present invention, this object is achieved by adapting the fin structure of a sailing device of the initially described type for generating a lift having a downward component .

During sailing in stronger winds, the downward component of the lift generated by the fin structure opposes the upward lift component of the wind resultant force. Due to this effec sails generating an upward lift component larger than the gravity forces exerted onto the device can be carried, without the device being lifted out of the water. At a suitable angle of the wind resultant force relative to the horizontal, at which angle the heeling moment and the counteracting moment due to the upward lift and the gravity are balanced out or are within a range within which these moments can be balanced out using the weight of the crew or of a ballast. This allows a sailing device of a given weight to carry more powerful sails, which generate an accordingly larger driving force, so the ratio between driving forces and water displacement is improved and, in principle, higher speeds can be achieved than with sailing device according to the state of the art.

If the sailing device according to the invention is provided in form of a sailing craft, the fin structure is preferably provided in form of a hydrodynamic fin or an assembly of hydrodynamic fins. However, if the sailing device is a sailing vehicle or an ice-sailer, the fin structure is preferably provided in form of an aerodynamic fin or an assembly of aerodynamic fins. The fins can be of a design similar to that used in racing cars to obtain so-called downforce and preferably make use of ground-effect in the form of a vacuum generated under the hull.

Preferably, the fin structure and the sail system are arranged, such that the upward lift genereated by the sail is operative along a line to leeward of a line along which the downward forces generated by the fin structure are operative. Thus the combination of upward lift generated by the sail and downward lift generated by the fin structure counteracts the heeling moment of the horizontal component of the wind resultant forces and the resistance of the device.

The sail system may comprise a kite freely flown at a line connected to the hull structure. It is then reliably ensured that the heeling moment exerted onto the device remains within certain manageable limits. If a more controlled sail system is preferred, the hull structure preferably comprises a hull and an extension movable between a position projecting to port of the hull and a position projecting to starboard of the hull. By attaching the foot portion of the sail system to the extension and arranging the attachment such that the foot of the sail system is movable between an end portion of the extension to port of the hull and an end portion of the extension to starboard of the hull, the foot of the sail can be held at a substantial lateral distance to both sides of the hull. Since the extension can be projected to both lateral sides of the hull, a single extension can be used which is extended at the side at which the foot of the sail system is to be held.

Accordingly, there does not have to be an extension at the opposite side of the device, which would increase the width and the weight of the device and would cause a substantial amount of wind resistance. Hereinafter, the invention is described in more detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of a presently most preferred embodiment of a sailing device according to the present invention;

Fig. 2 is a side view of an assembly comprising the hull structure and a fin structure of the sailing device shown in Fig. 1;

Fig. 3 is a front view of the assembly shown in Fig. 2; Fig. 4 is a side view of the fin structure of the assembly shown in Fig. 2 ;

Fig. 5 is a side view of an alternative fin structure; Fig. 6 is a schematic top view of the sail system; Figs. 7A and 7B are schematic top plan views showing the upwind starboard and port tack configurations of the sailing device according to Fig, 1;

Fig. 8 is a side view of a support hull; Fig. 9 is a front view of a second embodiment of the sailing device according to the invention;

Fig. 10 is a front view of a third embodiment of the sailing device according to the invention; and

Fig. 11 is a side view in cross-section of a hull of an ice-sailer according to the invention.

DETAILED DESCRIPTION OF A PREFERRED AND OTHER EMBODIMENTS OF THE INVENTION

The invention is first described with reference to the sailing craft shown in Figs. 1-4 and 6-8. Subsequently some other sailing crafts according to the invention are described. In the description and the drawings, like parts are indicated with like reference numerals.

As an initial matter, it is noted that the position in which the craft is shown in Fig. 1 is not an operative position, but a position chosen to clearly show the most relevant parts of the shown embodiment of th invention. Operative positions are shown in Figs. 7A and 7B and discuss hereinafter.

The sailing craft shown in Figs. 1-3, 6 and 7 comprises hull structure 1, a fin structure 2 and a sail system 3 havi a foot portion 4 and an upper portion 5. The sail system 3 i arranged to be trimmed with its foot portion 4 to leeward of its upper portion 5 and for generating a wind resultant forc including an upward lift component. The fin structure 2 is provided with a vertical main fin 6 and two laterally projecting secondary fins 7 for generating a lift having a downward component .

The hull structure 1 comprises a hull 8 and an extension 9 movable between a position projecting to port of the main hull 8 and a position projecting to starboard of the main hul 8. These extreme positions of the extensions 9, which are to be used during sailing upwind on the starboard and the port tack, are shown in Fig. 7A and 7B respectively. The foot portion 4 of the sail system 3 is attached to the extension 9 and movable between a port end portion 10 of the extension 9 and a starboard end portion 11 of the extension 9.

During sailing upwind in stronger winds, the sail system 3 is trimmed to lean with its upper portion 5 to windward by holding its foot portion 4 in a position to leeward of hull 8 Thus the sail will generate an upward lift component operativ along a line passing to leeward of the hull 8. Since the extension 9 and the sail system 3 are relatively light compared with the hull 8, this means that the line along whic O 96/11840 PC17NL94/00251

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the upward lift generated by the sail system 3 is operative will pass to leeward of the centre of gravity of the craft.

The upward lift generated by the sail system 3 therefore results in a moment counteracting the heeling moment caused by the horizontal components of the wind resultant force and the water resistance. If the sail system 3 is powerful enough, the upward lift generated thereby can be larger than the gravity force exerted onto the craft, since the downward lift generated by the secondary fins 7 pulls the craft down. This in turn makes it possible to sail with larger wind resultant forces operating at a given angle than without hydrodynamic fins for pulling the craft down and therefore also with larger driving forces, which in turn make it possible for the craft to .achieve higher speeds . The fin structure 2 and the sail system 3 are arranged, such that in use the upward lift component generated by the sail system 3 is operative along a line to leeward of a line along which the downward component generated by the fin structure 2 is operative. Thus the downward force generated by the fin structure 2 also contributes to counteracting the heeling moment caused by the lateral wind resultant force and the resistance of the craft in the water. In particular if the craft is of a light construction, the centre of gravity may also be to leeward of the line along which the upward component of the wind resultant force is operative. The craft is then mainly pulled down by the fin structure 2. The extension 9, which is movable from one side of the hull 8 to the other, provides a well controlled mounting facility for the foot portion 4 of the sail system 3, which can be spaced relatively far from the hull 8 and which only projects at the lateral side of the hull at which the foot of the sail system 3 is carried.

The extension 9 is pivotable about a vertical axis 12 extending through a mid plane of the hull 8. This allows to trim the extension 9 into a more forward position if it is desired to sail more off the wind. This is particularly advantageous during reaching off the wind, because the forwar position of the extension 9 allows to bring the line along which the upward lift generated by the sail system 3 is operative forward of the centre of gravity of the craft in order to counteract diving of the bow of the craft .

Apart from the main hull 8 and the extension 9, the hull structure 1 further comprises two extension support hulls 13, 14 spaced from the main hull 8 and spaced apart from each other at opposite sides of the extension 9 for supporting the extension 9 during sailing. The support hulls 13 and 14 increase the leeward heeling moment the craft can be subjected to without heeling so far that the extension 9 submerges. Submersion of the extension 9 while sailing at high speed would cause the craft to turn sharply to leeward and the substantial water resistance encountered by the extension as it dives in can easily cause damage to the vessel. Instead of with two support hulls 13, 14, the craft can also be provided with a single extension support hull, which may for example be preferable if the hull has a relatively great length so there is relatively little need for counteracting pitching of the craft . In the present embodiment, the main hull 8 and the extension support hulls 13, 14 are positioned in a triangular configuration, so that the craft is on the one hand stable, and on the other hand torsional moments between the hulls during sailing in rough seas are kept to a minimum. The foot 4 of the sail system 3 is movable from a part 10 of the extension 9 at the side of one of the extension support hulls 13 to a part 11 of the extension 9 at the side of the other one of the extension support hulls 14. Thus, the foot 4 of the sail can be held in a position almost transversely to leeward of the main hull 8 and near one of the support hulls 13, 14 while the other support hull 14 resp. 13 is held in a position essentially in front of the main hull 8. This is best shown in Figs. 7A and 7B. Thus the craft is particularly effectively supported against heeling by the leeward support hull 13 or 14 and particularly effectively supported against diving by the forward support hull 14 respectively 13.

The sail system 3 is carried by a support structure 15 comprising a main support rod 16 having a foot 17 at a corner 18 of the extension 9 adjacent the main hull 8 and two secondary rods 19, 20 each having a foot 21, 22 at a corner 11 resp. 10 of the extension 9 adjacent one of the extension support hulls 14 resp. 13. The support rods 16, 19, 20 converge to each other and are joined together at a level above the extension 9. The support rods 16, 19, 20 are hollow tubes, preferably made of carbon fibre composite material.

The sail system 3 further comprises an unstayed mast 23 carrying a sail 24. The sail system 3 is supported between it foot 4 and its top 5 by the support structure 15. The mast 23 is connected to the support structure 15 between its foot 25 and its top 26 via a traveller 27 which is movable along a rail 28 extending along a portion of the mast 23. By moving the foot 25 of the mast 23 along the extension 9 to a leeward corner 10 or 11 thereof, the inclination of th mast 23 and the sail 24 can be adjusted to accommodate the prevailing wind velocity. As the mast 23 is trimmed more vertical, the nearer the position of the traveller 27 will be to the foot 25 of the mast 23.

The stronger the wind, the more the mast 23 and the sail 24 is to be inclined to windward to keep the remaining heeling moment within a range which does not cause the craft to capsize. In light airs, the mast 23 is preferably trimmed in a virtually vertical orientation to maximize the projected sail area and to maximize the effectiveness of the sail system 3. One of the challenges of a crew of the proposed craft is to sail at different wind and water conditions with the sail 24 as vertical as possible, so that the driving force of the sail 24 is maximal, while capsizing is avoided.

The secondary support rods 19, 20 form a raked A-shaped structure supported by the main support rod 16. The rake of -li¬

the A-shaped structure 19, 20 is adjustable by adjusting at which position along the main support rod 16 the A-shaped structure 19, 20 meets the main support rod 16. If the rake of the A-shaped structure 19, 20 is increased, the sail 24 is further inclined to windward. This facility is particularly useful for obtaining a more vertical orientation of the wind resultant force and a reduced projected sail area in very strong winds.

The foot portion 4 of the sail system 3 is movable from a corner area 10, 11 of the triangle adjacent one of the extension support hulls 14 resp. 13 via a corner area 17 of the triangle adjacent the main hull 8 to a corner area 11 resp. 10 of the triangle adjacent the other one of the extension support hulls 14 resp. 13. To guide the foot 25 of the mast 23 along the sides of the triangle, the foot 25 of the mast 23 is supported by a traveller 29 which is guided by rails 30.

If it is desired to tack for example from the course shown in Fig. 7A to the course shown in Fig. 7B, a sheet (not shown) for controlling the angle of attack of the sail 24 is released and simultaneously, the foot 25 of the mast 23 is pulled toward the corner 17 of the extension 9 adjacent the main hull 8. Thus the sail 24 is generally displaced abaft of the main hull 8, which facilitates luffing into the wind. When the main hull 8 is passed through the wind, the foot 25 of the mast 23 is moved away from the corner of the extension 9 adjacent the main hull 8 to the corner 11 of the extension 9 in front of the main hull 8. Thus the sail 24 is moved forwar which facilitates bearing away to the new upwind course shown in Fig. 7B. As the new upwind course is approached, the extension 9 is pivoted to leeward to obtain the position shown in Fig. 7B. Also the pivoting to leeward of the extension 9 is supported by the wind resultant force exerted onto the sail system 3.

The extension support hulls 13, 14 are each pivotable relative to the extension 9 about a steering axis 30, 31 so the orientation of the extension support hulls 13, 14 can be adapted to the course of the craft and the position of the extension 9 relative to the main hull 8.

Furthermore, each of the extension support hulls 13, 14 has a centre of resistance abaft of steering axis 30, 31, so that the extension support hulls 13, 14 can automatically pivot into the course the craft is sailing.

As is best shown in Fig. 8 the extension support hulls 13, 14, are each pivotable relative to the extension 9 about a transversal axis 58 allowing pitching of the extension support hulls 13, 14 relative to the extension 9.

The extension support hulls 13, 14 each have a generally flat bottom 59 to form hydrofoils so the resistance at high speeds is reduced and the loads the extension support hulls 13, 14 can carry at speed are increased. The support hulls 13, 14 are each connected to a spring 60, urging the aft end of the support hull 13, 14 down, so that at high speeds and low loads of the support hulls the wetted surface of the support hulls 13, 14 is reduced. In combination with the springs 60, the support hulls 13, 14 form a resilient suspension of the extension 9, which ia advanatgeous in rough seas and during landing after jumps . To avoid oscillations of the support hulls 13, 14, furthermore dampers 61 are mounted between the support hulles and the extension 9.

To increase the directional stability of the craft, the support hulls 13, 14 are each provided with a fin 62. During sailing, the direction in which the forward support hull 13, 14 points is controlled by steering arms 74, 75, either by steering the forward support hull 13, 14 or by fixing it in a position in-line with the main hull 8. The leeward support hull 13, 14 is left free to pivot and follow the course of the craft. In the event, the main hull 8 is lifted out of the water, the leeward support hull 13, 14 provides virtually no lateral resistance, so the craft can drift to leeward. This causes a substantial reduction of the lateral wind resultant forces, so the craft will generally drop back to its normal sailing position.

In Fig. 4, the fin structure 2 is shown in more detail. The fin structure 2 comprises a rudder blade 32 which is controlled via a rudder pin 33 comprising a universal joint 34 and connected to a steering bar 35. The secondary fins 7 are each pivotable about an axis 36 and may be controlled via bars 37, 38 by pivoting the steering bar 35 about a transversal axis 39 coinciding the universal joint 34 as indicated by arrow 40. By operating the steering bar 35, the fins 7 can be operated to lift the craft out of the water at lower speeds and to pull the craft into the water as the upward lift generated by the sail system 3 threatens to lift the hull 8 out of the water. A particularly spectacular feature of the operable fins 7 is that, in stronger winds, the fins 7 can deliberately be operated to lift the craft quickly out of the water to make jumps. In flight, the craft can be stabilized by suitable movements of the crew. In the fin structure 2 shown in Fig. 5, the rods 37, 38 are connected via a third rod 41 pivotable about a transversal axis 42 to a water surface sensing member 43 such that, during sailing, the downward angle of the secondary fins 7 relative to the hull structure 8 - i.e. also the angle of attack - is increased if the water surface sensing member 43 looses contact with the water surface and moves downward. Thus the level of the main hull 8 relative to the water surface is automatically controlled. This level can be controlled to be such that the main hull 8 is spaced from the water surface to reduce the water resistance. The stability of the craft is nevertheless maintained by the extension support hulls 13, 14 at the far ends of the extension 9.

The sail system comprises a wishbone-shaped boom 44 of flexible material, preferably a composite of carbon fibre and epoxy resin. An outhaul line 45 interconnects the free ends of the boom 44 and is threaded through the aft end of the sail 24 and through one of the legs of the wishbone-shaped boom 44. If the outhaul line 45 is tensioned, the boom 44 is pulled into a configuration shown in dotted lines and the camber of the sail 24 is reduced. The stronger the wind, the more the outhaul should be tensioned. In Fig. 9 an embodiment of the craft according to the invention is shown in which the sail structure comprises a kite 46, attached to the hull 8 by freely pivotable lines 47, 48. The fin structure 2 consists of a single fin 49 which is laterally pivotable between a position shown in full lines and a position shown in dots and dashes. The angle of the fin 49 can be adjusted dependent of the angle of the lines 47, 48 and the forces exerted by the kite 46. Preferably, the fin is also tiltable about a longitudinal axis to obtain a particularly effective downward lift. The lines 47, 48 are attached to the hull 8 via a traveller 50 which is transversely slidable along a rail 51. By moving the traveller to leeward the resultant force of the lines 47, 48 can be brought as close as possible to the centre of water resistance of the craft, which is generally spaced below the hull 8.

In Fig. 10 an embodiment of the craft according to the invention is shown in which The extension 9 is laterally slidable between the positions projecting to port and to starboard of the hull 8. The foot 25 of the mast 23 is movable along a line 52 between the ends 10, 11 of the extension 9.

The angle of attack of the sail is controlled via a main sheet 53. When the mast is brought in a more vertical position, a connection 54 of the mast 23 to a support rod 55 is moved upward along a rail 56.

The downward lift generated by the fin strusctures operates along a line 71 to windward of the line 69 along which the upward component of the wind resultant force generated buy the sail system 3 operates. Thus the upward lif of the sail system 3 and the downward lift of the fin structure 2 contribute to counteracting the heeling moment resulting from the lateral components 72, 73 of the wind resultant force and the water resistance. To increase the distance between the line along which the lifting force generated by the sail operates 69 and the centre of gravity 7 of the craft, a helmsman or crew 57 should preferably be seated at the windward side of the hull 8 and hang out as in conventional dinghy. The transversal position of the crew 57 facilitates lateral balancing of the boat. The extension 9 is curved with a constant radius so that, on the one hand, the projecting end 10 or 11 is higher above the water surface ar.α, on the other hand, facilitate lateral sliding of the extensio 9.

The inclination to windward of the sail system 3 may also be controlled in other manners, for example by a hydraulic cylinder mounted between the support structure 15 and the mast 23 in a position spaced from the connection 54 of the mast 23 to a support rod 55 of the support structure 15.

In Fig. 11 a hull 8 of an ice-sailer according to the invention is shown which is fully integrated with the fin structure 2 into a fin-hull or wing-hull 2, 8. The basic configuration of the hull 8 and the extension 9 is similar to that of the sailing craft shown in Figs. 1-4 and 6-8, but instead of support hulls, support skates are provided. The hull 8 has a basically wing-shaped cross-section with lateral skirts 63 and a bottom 64 which rises from the front to the rear of the hull 8. In such a fast sailing devices, which achieve speeds which are a multiple of the prevailing wind velocity, the direction of attack of the apparent wind during sailing is mainly from the direction in which the device is moving, so during sailing a vacuum is generated under the hull or body 8. This vacuum pulls the hull 8 to the ice, so sails which generate an upward lift greater than the weight of the sailing device can be carried. The hull 8 is supported by fixed skates 65, 66. To steer the ice-sailer, the orientation of the extension 9 relative to the hull 8 is varied. The hull 8 is further provided with a seat 67 for a helmsman.

The skates 65 and 66 and also the skates supporting the extension 9 may be replaced by wheels to obtain a sailing cart or by skis to obtain a sailing sledge.

Finally, it is noted that the features of the invention relating to the rigging and the support of the sail system can as such also advantageously be applied in a device without a fin structure adapted for generating downward lift if the lift generated by the sail system remain low enough to be counteracted by the weight of the device and any persons and cargo on board. However, the ability to laterally project the foot of the sail relatively far to leeward is the more advantageous the larger the sails are. Typically, sails powerful enough to generate an upward lifting force larger than the gravity force exerted onto the device are relatively large.

Claims

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1. A sailing device comprising a hull structure (1), a fin structure (2) and a sail system (3) having a foot portion (4) and an upper portion (5) , wherein the sail system (3) is arranged to be trimmed with its foot portion (4) to leeward of its upper portion (5) and for generating a wind resultant force including an upward lift component, characterized in that the fin structure (2) is adapted for generating a lift having a downward component .

2. A sailing device according to claim 1, wherein the fin structure (2) and the sail system (3) are arranged, such that in use the upward lift component generated by the sail system (3) is operative along a line (69) to leeward of a line (71) along which the downward component generated by the fin structure (2) is operative.

3. A sailing device according to claim 1 or 2, wherein the hull structure (1) comprises a hull (8) and an extension (9) movable between a position projecting to port of the hull (8) and a position projecting to starboard of the hull (8) , the foot portion (4) of the sail system (3) being attached to said extension (9) and movable between port and starboard end portions (10, 11) of said extension (9) .

4. A sailing device according to claim 3, wherein said extension (9) is pivotable about a vertical axis (12) extending through a mid plane of the hull (8) .

5. A sailing device according to claim 4, wherein said hull a main hull (8) and the hull structure (1) further comprises at least one extension support hull (13, 14) spaced from the main hull (8) for supporting said extension (9) during sailing.

6. A sailing device according to claim 5, comprising two of said extension support hulls (13, 14) spaced apart from each other at opposite sides of the extension (9) .

7. A sailing device according to claim 6, wherein the main hull and the extension support hulls (13, 14) are positioned in a triangular configuration and wherein the foot portion (4 of the sail system (3) is movable from a part of the extensio (9) at the side of one of said extension support hulls (13, 14) to a part of the extension (9) at the side of the other one of said extension support hulls (13, 14) .

8. A sailing device according to claim 6, comprising a suppor structure (15) comprising a main support rod (16) having a foot at a corner of the extension (9) adjacent the main hull

(8) and two secondary rods (19, 20) each having a foot (21, 22) at a corner (10, 11) of the extension (9) adjacent one of said extension support hulls (13, 14), said support rods (16, 19, 20) converging to each other and being joined together at a level above said extension (9), wherein the sail system (3) further comprises a mast (23) having a foot (25) movable from a part of the extension (9) at the side of one of said extension support hulls (13, 14) to a part of the extension

(9) at the side of the other one of said extension support hulls (13, 14) and supported between its foot (25) and its top (26) by said support structure (15) .

9. A sailing device according to claim 8, wherein the secondary support rods (19, 20) form a raked A-shaped structure supported by said main support rod (16), the rake of said A-shaped structure being adjustable by adjusting at which position along said main support rod (16) said A-shaped structure meets said main support rod (16) .

10. A sailing device according to any one of the claims 7-9, wherein the foot (4) of the sail system (3) is movable from a corner area (10, 11) of the triangle adjacent one of the extension support hulls (13, 14) via a corner area (17) of the triangle adjacent the main hull (8) to a corner area (10, 11) of the triangle adjacent the other one of the extension (9) support hulls (13, 14) .

11. A sailing device according to any one of the claims 5-10, wherein the or each extension support hull (13, 14) is pivotable relative to the extension (9) about a steering axis (30, 31) .

12. A sailing device according to claim 11, comprising means (74, 75) for controlling the orientation of the or each support hull (13, 14) about the steering axis (30, 31) relative to the extension (9), wherein the or each support hull is provided with a fin member (62) .

13. A sailing device according to claim 11 or 12, wherein the or each extension support hull (13, 14) has a centre of resistance abaft of steering axis (30, 31) . 14. A sailing device according to any one of the claims 5-13 wherein the or each extension support hull (13, 14) is pivotable relative to the extension (9) about a transversal axis allowing pitching of the extension support hull (13,

14 relative to the extension (9) .

15. A sailing device according to any one of the claims 5-14 wherein the or each extension support hull (13, 14) has a generally flat bottom.

16. A sailing device according to claim 5 or 6 wherein the extension (9) is laterally slidable between said positions projecting to port and to starboard of the hull (8) .

17. A sailing device according to claim 1 or 2, wherein the sail system (3) comprises a kite (46), attached to the hull structure (1) by at least one freely pivotable line (47, 48) .

18. A sailing device according to claim 17, wherein said line (47, 48) is attached to the hull structure (1) via a transversely movable traveller (50) .

19. A sailing device according to any one of the preceding claims, wherein the fin structure (2) comprises a main fin (6 projecting downward from the hull structure (8) and at least one secondary fin (7) projecting laterally from the main fin (6) and arranged at an angle adapted for generating a downwar lift component, the or each secondary fin (7) being connected to a control member (37) for controlling the angle of said secondary fin (7) relative to the hull structure (1) .

20. A sailing device according to claim 19, wherein the control member (37) is connected to a water surface sensing member (43) such that, during sailing, the downward angle of said secondary fin (7) relative to the hull structure (1) increases in response to the water surface sensing member (43) loosing contact with the water surface.