SE544743C2

SE544743C2 - Hydrofoil for windsurfing

Info

Publication number: SE544743C2
Application number: SE2150480A
Authority: SE
Inventors: Martin Wahlgren
Original assignee: Consat Ab
Priority date: 2021-04-16
Filing date: 2021-04-16
Publication date: 2022-11-01
Also published as: WO2022220728A1; SE2150480A1; EP4323268A1

Abstract

A hydrofoil (2) for use on a windsurfing board (1) comprises: a mast (3) having a first end (31), arranged to be attached to the board, and an opposite second end (32); and a first foil assembly (4) comprising a first fuselage (41) attached to the second end (32) of the mast (3). The fuselage (41) extends in a forward direction from the mast, to a first forward end (42), and in a backward direction from the mast, to a first rearward end (43). A first front wing (5) is attached at, or in the vicinity of, the first forward end (42), and a first rear wing (6) is attached at, or in the vicinity of, the first rearward end (43). The hydrofoil (2) further comprises a second foil assembly (7) comprising a second fuselage (71) attached to the mast (3) at an intermediate position, between the first and second ends, and extending in a forward direction from the mast, to a second forward end (72). A second front wing (8) is attached to the second fuselage (71) at, or in the vicinity of, the second forward end (72).

Description

Technical field of the invention The present invention relates to a hydrofoil for use on a Windsurfing board, and also to a Windsurfing board comprising such a hydrofoil, as well as to a detacha ble foil assembly.

Background Hydrofoils have been used on boats for over 100 years. ln later years, hydrofoils have also been in Water sports, such as stand up paddle boarding, surfing, and kitesurfing. ln recent years hydrofoils have also been used on Windsurfing boards. Hereby, a hydrofoil is affixed under the board so as to allow the board to lift above the water level when the board is moved on the water at sufficient speed. Hydrofoils are very interesting as they offer less resistance to Water compared to the boards on which they are installed. This allow the user to travel at higher speed. ln particular, it allows a Windsurfer to travel at high speed at low and moderate wind speed.

Hydrofoils for Windsurfing are nowadays commercially available from several manufacturers. A conventional hydrofoil comprises a mast connected to the board, and extendíng downwards in an essentially vertical direction. Attached to a lower end ofthe mast is a fuselage, extendíng essentially in a horizontal direction, in the travelling direction of the board. At the ends of the fuselage, a front Wing and a rear Wing are attached. Examples of such conventional hydrofoils are e.g. known from US 9056654, US 9896158 and US 2020/ However, a general problem with known hydrofoils for Windsurfing is that it is difficult to find adequate size and dimensions for the wings. Larger wings are beneficial since they offer a higher lifting force at lower speed, thereby making it easier to lift the board from the Water surface and commence foiling. However, such larger wings have a greater resistance in the water, and greatly limits the maximum speed that can be obtained. Smaller Wings on the other hand have lower resistance in water, and thereby allows a greater maximum speed. However, with such smaller wings, it is more difficult to raise the board from the water surface, and it therefore becomes more cumbersome to start foiling, and takes considerably more time, in particular at lower wind speed. There is therefore a need for a hydrofoil with which foiling is easier to initiate, and which at the same time offers higher maximum speed, in particular at lower wind speed levels. lt is also a need for such solutions which can be provided in a cost-efficient manner.

Summary of the invention lt is therefore an object of the present invention to provide a hydrofoil for use on a Windsurfing board which at least alleviates the above-discussed problems.

This object is obtained by means of a hydrofoil in accordance with the appended claims.

According to a first aspect of the present invention there is provided a hydrofoil for use on a windsurfing board, the hydrofoil comprising: a mast having a first end, arranged to be attached to the board, and an opposite second end; a first foil assembly comprising a first fuselage attached to the second end of the mast, and extending in a forward direction from the mast, to a first forward end, and in a backward direction from the mast, to a first rearward end, a first front wing attached to the first fuselage at, or in the vicinity of, the first forward end, and a first rear wing attached to the fuselage at, or in the vicinity of, the first rearward end; and a second foil assembly comprising a second fuselage attached to the mast at an intermediate position, between said first and second ends, and extending in a forward direction from the mast, to a second forward end, and a second front wing attached to the second fuselage at, or in the vicinity of, the second forward end. ln the context ofthe present application, mast refers to the structure ofthe hydrofoil which is attached to the board, and which is arranged to extend generally vertically below the board. The mast is preferably relatively flat, with a width, in the travel direction of the board, greatly exceeding the thickness. The mast may have a height in the range of 50-120cm. ln the context ofthe present application, fuselage refers to a structure extending out from the mast, at a distance from the board. The fuselage generally extends in the travel direction of the board, and may extend forwardly and/or backwardly, with reference to the travel direction. The fuselage is preferably extending essentially horizontally. The fuselage, when carrying both a front Wing and a rear Wing, may have a length in the range of 50-100 cm, and preferably in the range of 60-95 cm, and most preferably in the range of 75-90 cm. A fuselage carrying only a front Wing, and extending only in the forward direction from the mast, may have a length in the range of 25-60 cm, and preferably in the range of 30-50 cm, and most preferably in the range of 35-45 cm.

The present invention is based on the realization that the size of the wings for a hydrofoil used for Windsurfing is generally a trade-off. With a larger Wing, the lifting force will increase, and the board will be lifted up above the water surface at lower speed. However, when the board is lifted up in the air, a larger Wing will reduce the speed, and a smaller Wing will have less resistance in the water, and will allow a greater speed. By means of the present invention, this problem is significantly reduced. The lower first foil assembly can be relatively small, with dimensions sufficient to lift the board above the water surface only at relatively high speed. However, the one or more additional foil assembly, i.e. the second foil assembly and optionally also a third foil assembly, will contribute to the lifting force at low speed. Thus, at low speed, the first and second foil assemblies, and also an optional third foil assembly, will together contribute to the lifting of the board above the water surface. Thus, the board will be lifted up in the air at much lower speed than if only the first foil assembly had been available. As the board rises above the water surface, the board will quickly gain speed. As the speed increases, and reaches a certain level, the lifting force will be great enough to lift also the second foilassembly, and/or the optional third foil assembly, up above the water surface. Hereby, the water resistance decreases, and the board will travel even faster.

Thus, the hydrofoil comprising two or more foil assemblies functions in a similar way as for a vehicle with a gear box. At low speed you use a low gear, providing great force but at a relatively low speed, and when the speed increases you shift to a higher gear, thereby enabling travel at a higher speed. The new hydrofoil can consequently be said to provide automatic gearing, similar to the operation of an auto gear system or automatic transmission system.

Since initial lifting force is provided by the second foil assembly, a much smaller first foil assembly can be used, compared to what is conventionally used, thereby allowing the board to travel at very high speed already at low or modest wind speed. lt will e.g. be possible to travel at 20 knots or more already at low wind speeds such as 4-6 m/s. At the same time, the second foil assembly, and also the optional third foil assembly, will ensure that foiling will be initiated very rapidly, and that the board will be lifted above the water surface after a very short period of time.

The first front wing is preferably shaped and dimensioned to lift the board over the water surface when the speed of the board is above a first threshold level. The second front wing may be shaped and dimensions to provide an additional lifting force for lifting the board over the water surface when the speed of the board is below said first threshold level.

The second foil assembly may comprise only one wing. However, alternatively, the second fuselage may further extend in a rearward direction from the mast, to a second rearward end, and a second rear wing may be attached to the second fuselage at, or in the vicinity of, the second rearward end. The addition of a rear wing also to the second foil assembly increases stability to the board when foiling.

The hydrofoil may comprise only two foil arrangements, i.e. the first and second foil assemblies. However, alternatively, the hydrofoil may further comprise a third foil assembly comprising a third fuselage attached to the mast at an intermediate position, between said first and second ends, and extending in a forward direction from the mast, to a third forward end, and a third front wing attached to the third fuselage at, or in the viciníty of, the third forward end, the third foil assembly being arranged between the second foil assembly and the first end ofthe mast, or between the second foil assembly and the second end of the mast. With the use of such a third foil assembly, the ”automatic transmission” provided by the hydrofoil will be provided with an additional "gear". Hereby, the foil arrangements will sequentially be lifted up above the water surface as the board gains speed. lf e.g. the third foil assembly is arranged above the second foil assembly, all foil assemblies will initially be in the water, and will all contribute to lift the board above the water surface. At a certain first speed, the first and second foil assemblies will provide sufficient lifting force to lift the third foil assembly over the water surface. At a higher second sped, the first foil assembly will provide sufficient lifting force to lift also the second foil assembly above the water surface. Hereby, an even smaller first foil assembly may be used, thereby enabling an even higherfinal speed.

Thus, the first front wing and the second front wing are preferably shaped and dimensioned to lift the board over the water surface when the speed of the board is below a first threshold level, and wherein the first front wing is shaped and dimensioned to lift the board and the second front wing over the water surface when the speed of the board is above the first threshold level. ln each foil assembly, the lifting force is preferably primarily provided by the front wing, whereas the rear wing is used primarily for stabilization. However, in embodiments, a lifting force may also be provided by the rear wing.

Thus, more generally, the first foil assembly and the second foil assembly are preferably arranged to lift the board over the water surface when the speed of the board is below a first threshold level, and wherein the first foil assembly is arranged to lift the board and the second foil assembly over the water surface when the speed of the board is above the first threshold level.

The first threshold level is preferably in the range of 3-6 m/s.

The third foil assembly may comprise only one Wing. HoWever, alternatively, the third fuselage may extend also in a rear\Nard direction from the mast, to a third rearWard end, and a third rear Wing may be attached to the third fuselage at, or in the vicinity of, the third rearward end. The addition of a rear Wing also to the third foil assembly increases stability to the board When foiling.

When a third foi| assembly is used, only one of the second and third foil assemblies may be provided With a rear Wing.

At least one ofthe second front Wing and the optional third front Wing may have essentially the same shape and dimensions as the first front Wing. HoWever, at least one of the shape and dimensions of the second and/or third front Wing may be different from the first front Wing. For example, the second and/or third front Wing may be larger than the first front Wing, thereby providing a greater lifting force, but also a greater Water resistance.

The second front Wing, and also the optional third front Wing, are preferably arranged essentially vertically overlying the first front Wing. HoWever, in embodiments, one or both ofthe second and third front Wings may be displaced in relation to the first front Wing, in a forward or backWard direction. Such displacements may be used to alter the balance of the board When foiling The second fuselage and/or third fuselage may be detachably attached to the mast. Hereby, the hydrofoil may be adapted to be used only With one foi| assembly, or With tWo or three foil assemblies. For example, a user may use only one foil assembly When there is relatively strong Wind, and use tWo or more foil arrangement When there is less Wind. A detacha ble fuselage may also be used to retrofit conventional hydrofoils With one or more additional foil assemblies.

The second foil assembly may be arranged in an essentially intermediate position between the first and second end ofthe mast, the distance to each of the first and second end being at least 30% of the total distance between the first and second end, and preferably at least 40%, and most preferably at least 45%. HoWever, alternatively, the second foil may be arranged closer to the board or closer to the first foil assembly.

According to another aspect of the invention, there is provided a wind surfing board comprising an upper side and a lower side, and a hydrofoil as discussed in the foregoing attached to the lower side of the board.

According to yet another aspect of the invention, there is provided a detachable foil assembly for arrangement on a mast of a hydrofoil, the foil assembly comprising a fuselage detachably connectable to a mast ofa the hydrofoil in an intermediate position thereof by a connection member, the fuselage extending in a forward direction from the connection member, to a forward end, and further comprising a front Wing attached to the fuselage at, or in the vicinity of, the forward end.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

Brief description of the drawinqs For exemplifying purposes, the invention will be described in closer detail in the following with reference to embodiments thereof illustrated in the attached drawings, wherein: Fig. la-c are views of a hydrofoil in accordance with a first embodiment of the present invention, wherein Fig. la is a perspective view from the side, Figs. lb and lc are cross-sectional views of the hydrofoil of Fig. la taken along a width direction B-B and a longitudinal direction C-C, respectively; Fig. 2 is a perspective view from the side of a hydrofoil in accordance with another embodiment ofthe present invention; Fig. 3 is a perspective view from the side of a hydrofoil in accordance with yet another embodiment ofthe present invention; Figs. 4a-b are schematic side views of some various alternative shapes of the wings; and Figs. 5a-f are schematic top views of some various alternative shapes of the wings.

Detailed description of preferred embodiments ln the following detailed description preferred embodiments of the invention embodiments are exchangeable between the embodiments and may be combined in different ways, unless anything else is specifically indicated. lt may also be noted that, for the sake of clarity, the dimensions of certain components illustrated in the drawings may differ from the corresponding dimensions in real-life implementations of the invention.

The disclosed hydrofoil is particularly intended for Windsurfing, and for attachment to windsurfing boards. lt is believed that the hydrofoil would be of greatest advantage for such applications. However, the hydrofoil may nonetheless also be used for other types of self-propelled water sport boards, e.g. manually powered water sport boards, such as stand up paddle boards, other types of wind powered water sport boards, such as kitesurfing boards, or wave powered water sport boards, such as conventional surfing boards.

With reference to Figs. 1a-c, a hydrofoil 2 is connected to a Windsurfing board 1. The hydrofoil is connected to the bottom side of the board and at, or in the vicinity of, the aft end of the board. Connection of the hydrofoil to the board may be provided in various ways, as is per se known in the art, such as by bolts and the like.

The hydrofoil comprises a mast 3, extending essentially in a vertical direction.

The mast 3 has a first, upper end 31, arranged to be attached to the board 1, and an opposite second, lower end 32. The mast is preferably essentially flat, in order to reduce the resistance when moved in the water. The mast may e.g. have a vertical length of about 50-120cm, a width, in the travel direction, ofabout 5-15 cm, and a thickness, in a direction perpendicular to the travel direction, of about 1-5 cm.

A first foil assembly 4 is connected to the second end 32 of the mast. The first foil assembly comprises a first fuselage 41, connected to the mast. The first fuselage is elongate, and extends essentially horizontally in the travel direction. A first part of the fuselage extends from the mast in a forward direction, ending with a first forward end 42, and a second part of the fuselage extends from the mast in a rearward direction, ending with a first rearward end 43. The first fuselage may have a circular cross-section, but other shapes are also feasible, such as a square or rectangular cross-section, and oval cross-section, or the like.

Attachment of the first fuselage 41 to the mast end 32 can be obtained in various ways, as is per se known in the art. The connection may e.g. be a releasable connection, e.g. formed by bolts or the like. However, preferably the connection is a permanent connection. ln one embodiment, the first fuselage 41 may be integrally formed with the mast A first front wing 5 is connected to the first fuselage 41, at, or in the vicinity of, the first forward end 42. The first front wing extends laterally and symmetrically on both sides of the fuselage. The first front wing generally extends horizontally, and with a length direction being perpendicular to the travel direction of the board.

The first front wing is shaped to provide a lifting force when moved through the water. The shape of the wing may e.g. be arranged to provide a pressure difference between the upper surface and lower surface of the wing, results in a lifting force acting to lift the board. At a certain speed, the lift produced by the wing, and possibly in combination with a lifting force from further wings, equals the weight of the board and the rider, and the board comes out of the water.

A first rear wing 6, which may also be referred to as the tail, is connected to the first fuselage 41, at, or in the vicinity of, the first rearward end 43. The first rear wing also extends laterally and symmetrically on both sides ofthe fuselage. The first rear wing generally extends horizontally, and with a length direction being perpendicular to the travel direction of the board.

The first rear wing 6 may have smaller dimensions than the first front wing 5, and may have the primary purpose of providing stability. However, the first rear wing 6 may also provide a certain lifting force.

Further, a second foil assembly 7 is provided, and arranged at an intermediate position, between the board and the first foil arrangement 4. The second foil assembly comprises a second fuselage 71, connected to the mast. The second fuselage is elongate, and extends essentially horizontally in the travel direction. A part of the fuselage extends from the mast in a forward direction, ending with a second forward end 72. The second fuselage may comprise only this part extending forwardly. However, alternatively the fuselage may also comprise a second part of the fuselage extending from the mast in a rearward direction, ending with a second rearward end 73. The second fuselage may be similarly shaped as the first fuselage, and may e.g. have a circular cross-section, but other shapes are also feasible, such as a square or rectangular cross-section, and oval cross-section, or the like.

Attachment of the second fuselage 71 to the mast can be obtained in various ways. The connection may e.g. be a fixed, permanent connection, e.g. obtained by welding. The second fuselage may also be integrally formed with the mast. However, in a preferred embodiment, the second fuselage is connected to the mast by a releasable connection, making the second foil assembly detachable from the mast. Such a releasable connection may e.g. be formed by bolts or the like. The bolts may interact directly with the mast, e.g. by being screwed into holes formed in the mast. However, the releasable connection may also be formed by clamping the fuselage onto the mast. ln such an embodiment, the fuselage may be bifurcated towards one end, and the bifurcated parts may be brought together by a bolt arrangement or the like to clamp the fuselage onto the mast.

A second front wing 8 is connected to the second fuselage 71, at, or in the vicinity of, the second forward end 72. The second front wing extends laterally and symmetrically on both sides of the fuselage 71. The second front wing generally extends horizontally, and with a length direction being perpendicular to the travel direction of the board.

The second front wing is preferably shaped similar to the first front wing, and is also arranged to provide a lifting force when moved through the water. At a certain speed, the lift produced by the two front wings, and possibly in combination with a lifting force from further wings, equals the weight of the board and the rider, and the board comes out ofthe water. As the speed increases further, the lifting force of the first front wing 5 will be sufficient to lift also the second foil assemblyout of the water, thereby further reducing the water resistance, and thereby enabling an even higher speed.

The second foil assembly may comprise only one Wing, i.e. the front Wing 8, as in the embodiment of Figs. 1a-c. However, alternatively, the second foil assembly may also comprise an additional second rear Wing 9, as in the illustrative example of Fig. 2. The second rear Wing 8 is preferably connected to the second fuselage 71, at, or in the vicinity of, the second rearward end 73. The second rear Wing also preferably extends laterally and symmetrically on both sides of the fuselage. The second rear Wing generally extends horizontally, and with a length direction being perpendicular to the travel direction of the board.

The second rear Wing 8 may have smaller dimensions than the second front Wing 7, and may have the primary purpose of providing stability. However, the second rear Wing 8 may also provide a certain lifting force.

Apart from the addition of the second rear Wing, the embodiment of Fig. 2 corresponds to the embodiment discussed in relation to Figs. la-c.

The hydrofoil may comprise only two foil arrangements, i.e. the first and second foil assemblies. However, alternatively, the hydrofoil may further comprise a third foil assembly 10, as in the illustrative example of Fig. 3. The third foil assembly 10 may comprise a third fuselage 101 attached to the mast at an intermediate position, between the first end 31 and second end 32, and extending in a forward direction from the mast 3, to a third forward end. A third front Wing 11 may be attached to the third fuselage 101 at, or in the vicinity of, a third forward end 102. The third foil assembly 10 may be arranged between the second foil assembly 7 and the first end 31 ofthe mast, or between the second foil 7 assembly and the second end 32 of the mast. With the use of such a third foil assembly, the lifting of the board above the water surface will occur in three steps, as the board gains speed. First, all the three foil assemblies will be in the water, and contribute to a lifting force raising the board above the water surface. As speed increases, one of the intermediate foil assemblies, here the third foil assembly 10, will be lifted above the water surface, thereby reducing the water resistance. As the speed increasesfurther, also the other intermediate foil assembly, here the second foil assembly 7, Will be lifted above the Water surface, thereby decreasing Water resistance even further. Hereby, the foil arrangements Will sequentíally be lifted up above the Water surface as the board gains speed. ln the illustrative example of Fig. 3, the second foil assembly 7 and the third foil assembly 10 each comprises only a front Wing. However, one or both of said foil assemblies may also comprise an additional rear Wing, in analogy With the discussion With reference to Fig. 2 above.

The third foil assembly may be formed similarly to the second foil assembly, as discussed in the foregoing. Further, connection of the third foil assembly to the mast may be achieved in similar Ways as discussed in relation to the second foil assembly.

When a third foil assembly is used, the third front Wing may be shaped and dimensioned similarly to the second and/or first front Wings. However, the third front Wing may also be larger or smaller compared to these, and/or shaped differently. Similarly, a third rear Wing may be shaped and dimensioned similarly to the second and/or first rear Wings. However, the third rear Wing may also be larger or smaller compared to these, and/or shaped differently.

Apart from the addition ofthe third rear Wing, the embodiment of Fig. 3 corresponds to the embodiment discussed in relation to Figs. la-c and The second front Wing, and also the optional third front Wing, are preferably arranged essentially vertically overlying the first front Wing. This position generally is in line With the balance position of the person standing on the board. Thus, the person standing on the board generally has his/her feet on different sides of the position of the first front Wing, and consequently also on different sides of the second and third front Wings. However, in embodiments, one or both of the second and third front wings may be displaced in relation to the first front Wing, in a forward or backWard direction. Such displacements may be used to alter the balance of the board When foiling.The second fuselage and/or third fuselage may be detachably attached to the mast. Hereby, the hydrofoil may be adapted to be used only with one foil assembly, or with two or three foil assemblies. For example, a user may use only one foil assembly when there is relatively strong wind, and use two or more foil arrangement when there is less wind. A detacha ble fuselage may also be used to retrofit conventional hydrofoils with one or more additional foil assemblies.

The front and rear wings of the first, second and third foil assemblies may be shaped in the same way, or in different ways. Some alternative shapes for the wings will be discussed in the following. ln the embodiments of Figs. la-c, 2 and 3, the wings are shaped as having an essentially rectangular shape, when seen from the side. However, the wings may also have other side-view shapes. For example, the wings may have a curved shape, as illustrated in Fig. 4a, or with the wing parts forming an angle, into an obtuse V- shape, as illustrated in Fig. 4b. ln such an arrangement, the end parts of the wings will be higher in the water than the central part. However, many other shapes are also feasible. For example, the wings may have an undulated form, e.g. having a deeper central part, on each side moving up to a lifted intermedíate part, and continuing into a higher outer part.

Further, in the embodiments of Figs. la-c, 2 and 4, the wings, when seen from above, have a generally rectangular shape. However, the wings may also have other top-view shapes. For example, the wings may have rounded corners, or even having the shape of an oval, as shown in Fig. 5a. Additionally, the wing parts may form an angle, into an obtuse V-shape, as illustrated in Fig. 5b. ln such an arrangement, the end parts of the wings will be farther away from the front end of the board than the central part. The wings may also have the shape of a triangle, or a truncated triangle, as illustrated in Fig. 5c. Alternatively, the wings may have the shape of a truncated triangle extending into a generally rectangular part, as illustrated in Fig. 5d. A front end of the wing may also have a curved outline, as illustrated in Fig. 5e. Further, both the front end and the rear end of the wing mayhave curved shapes, forming a lunar shaped Wing, as illustrated in Fig. 5f. ln all the embodiments, the corners may be relatively sharp or rounded.

The Wings, the fuselages and the mast may be formed by the same or by different materials. The material(s) may e.g. be one or several of carbon, carbon composite material, aluminum and plastic material, such as polypropylene and high density polyethylene. The plastic material may also be reinforced with fibers, such as Kevlar, fiberglass or carbon.

As discussed in the foregoing, the various parts may be manufactured as one piece, or as su b-combination of pieces.

The mast of the hydrofoil may be affixed to the board in any means known in watersports for fixing fins, such as with bolts.

Specific embodiments of the invention have now been described. However, several alternatives are possible, as would be apparent for someone skilled in the art. For example, one or more intermediate foil assemblies may be used, and with or without an additional rear Wing. Further, all the front wings and rear wings may be similarly shaped and dimensioned, or having varying properties.

Such and other obvious modifications must be considered to be within the scope of the present invention, as it is defined by the appended claims. lt should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. ln the claims, any reference signs placed between parentheses shall not be construed as limiting to the claim. The word "comprising" does not exclude the presence of other elements or steps than those listed in the claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. Further, a single unit may perform the functions of several means recited in the claims.

Claims

1. A hydrofoil (2) for use on a Windsurfing board (1), the hydrofoil comprising: a mast (3) having a first end (31), arranged to be attached to the board, and an opposite second end (32), a first foil assembly (4) comprising a first fuselage (41) attached to the second end (32) of the mast (3), and extending in a forward direction from the mast, to a first forward end (42), and in a backward direction from the mast, to a first rearward end (43), a first front Wing (5) attached to the first fuselage (41) at, or in the vicinity of, the first forward end (42), and a first rear Wing (6) attached to the fuselage (41) at, or in the vicinity of, the first rearward end (43), esk' a second foil assembly (7) comprising a second fuselage (71) attached to the mast (3) at an intermediate position, between said first and second ends, and extending in a forward direction from the mast, to a second forward end (72), and a second front Wing (8) attached to the second fuselage (71) at, or in the vicinity of, the second forward end (72).

2. The hydrofoil of claim 1, wherein the first front Wing (5) is shaped and dimensioned to lift the board (1) over the water surface when the speed of the board is above a first threshold level.

3. The hydrofoil of claim 2, wherein the second front Wing (8) is shaped and dimensionggegyis. to provide an additional liftingforce for lifting the board (1) over the water surface when the speed of the board is below said first threshold level.

4. The hydrofoil of any one ofthe preceding claims, wherein the second fuselage (71) further extends in a rearward direction from the mast (3), to a second rearward end (73), and an second rear Wing (9) attached to the second fuselage (71) at, or in the vicinity of, the second rearward end (73).

5. The hydrofoil of any one ofthe preceding claims, further comprising a third foil assembly (10) comprising a third fuselage (101) attached to the mast (3) at an intermediate position, between said first and second ends, and extending in aforward direction from the mast, to a third forward end (102), and a third front wing (11) attached to the third fuselage (101) at, or in the vicinity of, the third forward end (102), the third foil assembly (10) being arranged between the second foil assembly (7) and the first end (31) of the mast, or between the second foil assembly (7) and the second end (32) ofthe mast.

6. The hydrofoil of claím 5, wherein the third fuselage (101) further extends in a rearward direction from the mast (3), to a third rearward end, and an third rear wing attached to the third fuselage at, or in the vicinity of, the third rearward end.

7. The hydrofoil of any one ofthe preceding claims, wherein the second front wing (8) has essentially the same shape and dimensions as the first front wing (5)-

8. The hydrofoil of any one ofthe claims 1-6, wherein at least one of the shape and dimensions of the second front wing (8) is different from the first front wing (5).

9. The hydrofoil of any one ofthe preceding claims, wherein the second fuselage (71) is detachably attached to the mast (3).

10. The hydrofoil of any one ofthe preceding claims, wherein the second foil assembly (7) is arranged in an essentially intermediate position between the first and second end of the mast, the distance to each of the first and second end being at least 30% of the total distance between the first and second end, and preferably at least 40%, and most preferably at least 45%.

11. The hydrofoil of claím 1, wherein the first front wing (5) and the second front wing (8) are shaped and dimensioned to lift the board (1) over the water surface when the speed of the board is below a first threshold level, and wherein the first front wing (5) is shaped and dimensioned to lift the board and the second front wing (8) over the water surface when the speed of the board is above the first threshold level.

12. The hydrofoil of claím 1, wherein the first foil assembly (4) and the second foil assembly (7) are arranged to lift the board (1) over the water surfacewhen the speed of the board is below a first threshold level, and wherein the first foil assembly is arranged to lift the board and the second foil assembly (7) over the water surface when the speed of the board is above the first threshold level.

13. The hydrofoil of claim 2, 3, 11 or 12, wherein the first threshold level is in the range of 3-6 m/s.

14. A wind surfing board (1) comprisíng an upper side and a lower side, and a hydrofoil (2) in accordance with any one of the claims attached to the lower side ofthe board.

15. A detachable foil assembly for arrangement on a mast (3) of a hydrofoil (2), the foil assembly comprising a fuselage (71; 101) detachably connectable to a mast (3) of a the hydrofoil (2) ín an intermediate position thereof, between a first end (31) of the mast arranged to be attached to the board and an opposite second end (32), by a connection member, the fuselage extending in a forward direction from the connection member, to a forward end (72, 102), and further comprising a front wing (8, 11) attached to the fuselage (71; 101) at, or in the vicinity of, the forward end (72, 102).