WO1993009994A1

WO1993009994A1 - A vehicle for use on water

Info

Publication number: WO1993009994A1
Application number: PCT/AU1992/000602
Authority: WO
Inventors: Michael Baranski
Original assignee: Michael Baranski
Priority date: 1991-11-14
Filing date: 1992-11-09
Publication date: 1993-05-27

Abstract

A vehicle for use on water comprising a body (40) having a front and back leg (41, 42). The front leg (41) has four fins on it, the three uppermost fins being uplift fins and the lowermost fin being a downlift fin. The back leg (42) has a single fin which when at a 0° angle of incidence with respect to the direction of motion of the vehicle, provides neither uplift or downlift. The front leg (41) is pivotally connected to the body (40) through a parallelogram linkage (52, 49b, 60) which is pivoted to the body (40) at pivot points (54 and 56). The parallelogram linkage (52, 49b, 60) maintains the front leg (41) in a predetermined orientation with respect to the direction of motion of the vehicle.

Description

A Vehicle For Use On Water The present invention is particularly relevant t sail-craft and is also relevant to hydrofoil water-craft.

Attempts have been made to improve the speed an efficiency of water-craft by incorporating a hydrofoi concept into monohull and multihull sailing craft

Unfortunately, such craft were restricted by wind and wate conditions which severely effected their stability.

In 1972 C. Hooks came up with the idea o adjusting the foil angle of incidence with respect to th direction of motion of a craft, in an attempt to gai hydrofoil craft rolling stability where hydroblades ar controlled by canard displaced buoyant bodies which act as water level sensors for input to a mechanical control system. Unfortunately, the mechanical control syste required complex hydraulic and electrical controls whic made the craft far to complex and expensive to produce.

A later development provided a watercraft having foils with adjustable angle of attack controlled by a canard cantilever and buoyant bodies acting as water level sensors. Unfortunately, such a craft was ineffective in choppy water conditions and suffered from sever high frequency vibration with increasing speed of the craft.

According to one aspect of the present invention there is provided a vehicle for use on water comprising a body part and at least one lift leg for supporting the body part, the or each lift leg comprising a downlift fin for applying a downwardly directed hydrodynamic force on the lift leg and an uplift fin for applying an upwardly directed hydrodynamic force on the lift leg, whereby in use, the lift leg is prevented from lifting completely out of water as the vehicle moves on water, by the downlift fin. Preferably the body part comprises one or more non lift legs for supporting the body part.

The non lift leg may be arranged to apply no uplift or downlift force when at a zero angle of incidence with respect to the direction of motion of the vehicle.

The body part may be arranged to carry a passenger. The body part may be arranged to move over water above the level of the water.

Preferably the downlift fin is located on a lower part of the lift leg.

It is preferred that all uplift fins are located above the one downlift fin.

According to another aspect of the present invention a vehicle is provided for use on water comprising a body part having a front leg and a back leg, one of the legs having a downlift fin for applying a downwardly directed hydrodynamic force on the leg and at least one uplift fin for applying an upwardly directed hydrodynamic force on the leg, the other leg being a balance leg having a fin which is for applying an upwardly directed hydrodynamic force when at a positive angle of incidence with respect to a forward direction of motion of the vehicle and for applying a downwardly directed hydrodynamic force when at a negative angle of incidence with respect to the forward direction of motion, wherein the downlift fin prevents the one leg from lifting completely out of the water.

It is preferred that the balance leg be the non lift leg.

The one leg may be oriented with respect to the intended forward direction of motion so that the downlift fin is always provided with a negative angle of incidence with respect thereto.

The one leg may also be oriented with respect to the intended forward direction of motion so that the uplift fin is always provided with a positive angle of incidence with respect to the forward direction of motion.

The front leg may be the one leg.

The body part preferably comprises an additional back or front leg .

Preferably if there is an additional back leg, only the front leg has downlift and uplift fins.

The body part may comprise left and right side body parts with back legs respectively being arranged to be attached thereto.

The vehicle may be wind powered.

It is preferred that the vehicle is a trimaran or catamaran with one lift leg and non lift leg on each outrigger hull and a balance leg on the main hull. The vehicle may be a motor powered boat. Preferably the body part is the hull of a boat. The left and right body parts may be outriggers. It is preferred that the height of the sails are determined by the height of each balance leg and the distance from the central hull and one outrigger hull.

Preferably the uplift fin or fins are angled at no greater than 30° with respect to the direction of motion of the vehicle. It is preferred that all uplift fins are located above all downlift fins.

The fins may each be in the form of a horizontally extending wing.

The shape of each fin is preferably of an NACA symmetrical profile.

The fins may each be provided with upper and lower arcuate surfaces for enabling a hydrodynamic force to be applied by the fin either upwardly or downwardly, as the case may be. Each fin may extend laterally on either side of the lift leg.

It is preferred that the lift leg be located at a front portion of the body part.

The body part may be provided with two non lift legs provided on opposite sides of the body part.

The body part may be provided with two non lift legs on opposite sides thereof.

The two non lift legs may be provided near a rear portion of the body part.

Each non lift leg may be provided with a non lift fin at its lower end.

The lift leg may be provided with two or more uplift fins and one downlift fin.

Each uplift fin is preferably evenly spaced apart from an adjacent uplift fin.

The lift leg may be located at the rear of the body part. The non lift legs may be located at the front of the body part.

The body part extends preferably in a substantially horizontal plane.

The lift leg may be pivotable with respect to the body part.

The lift leg may be automatically pivoted to a predetermined position with respect to the body part dependent upon the speed of the body part.

According to one embodiment both legs are fixed but the fins are pivotable.

The fins may be maintained at a predetermined orientation with respect to the direction of motion of the vehicle by a controlling means, the predetermined orientation enabling each fin to provide a maximum level of hydrodynamic force.

The controlling means preferably comprises a lever pivotally connected to a top portion of the lift leg, the lever being moveable to pivot the lift leg about a pivot point. The control means may comprise a parallelogram linkage with the lift leg connected to a first .link of the linkage.

Preferably the parallelogram linkage comprises two pairs of parallel links pivotally connected together so that each pair of links may be moved with respect to the other pair of links.

Preferably the first link is located at one end of the parallelogram linkage. Preferably second and third links of the parallelogram linkage are arranged to be parallel and maintained in a substantially horizontal configuration.

The body part preferably comprises left and right arms each having a non lift leg.

Each of the right and left arms preferably have a lift leg.

Preferably all legs are lift legs.

Each lift leg may be angled forward of a vertical axis.

Each non lift leg is preferably angled with respect to a vertical axis.

Each fin may have a different width or length.

The or each downlift fin may be smaller in length than the uplift fin immediately above it.

Preferably the lift leg when located at the front of the parallelogram linkage is pivotable about one of the pivots and is slidably connected to the first link. Preferably the lift leg is the front leg and is pivoted to the pivot connecting the first and second links.

Preferably the second link is lower than the third link. Preferably a fourth link is parallel to the first link.

The first link may comprise a slot across its width which is arranged to receive a portion of the lift leg, which portion is slidable within the confines of the slot to limit movement of the leg about the one pivot.

The portion of the lift leg may be fixed in a position within the slot.

The second link may be connected between the one pivot and a second pivot of the body part. The third link may be connected between a third pivot on an upper portion of the first link and a fourth pivot connected to the body part above the second pivot.

It is preferred that the second pivot be - o - connected to the hull of a boat.

The third pivot may be connected to an outrigger arm of the hull.

Preferably the outrigger arm of the hull is pivotally connected through the fourth link to the hull. Preferably the fins are arranged in parallel. It is preferred that the second and third links be connected together by a damping means.

The second and third links preferably are connected together through a stiffening means arranged to limit load carried by the first and fourth pivots.

Preferably each of the pivots are arranged to extend in a horizontal axis perpendicular to the direction of motion of the vehicle. The links may extend in the direction of motion of the vehicle.

The or each non lift leg is preferably pivotable about a pivot extending horizontally in the direction of motion of the vehicle i.e., from the front to the rear of the vehicle.

The length of the second and third links may be differen .

Preferably the lengths of the legs are different. A fourth link is preferably pivotally connected to the second and third links at a rear end of the body part.

The third pivot may be connected to an arm of the body part. The fourth pivot is preferably connected to the leg of the arm.

Each arm may be connected to a respective left/right body part.

Each arm may be pivotable with respect to its left/right body part.

Each arm may extend horizontally perpendicular to the length of a central body part.

The lift leg may be in front of the central body part and may be steerable to change its angle with respect to a central longitudinal axis of the central body part.

The leg in front of the central body part may be a non lift leg.

The rear non lift legs may be angled outwardly laterally with respect to a vertical axis.

The vehicle may be provided with automatic pitch and roll control. Preferably the vehicle comprises a main hull with a front leg and left and right side legs.

Preferably the left and right side legs are located at the rear of the hull.

Preferably the front leg is the lift leg and the left and right side legs are balance legs.

Preferably the front leg may be steered by a person seated in the hull.

Preferably the front leg comprises an upper lateral arm the ends of which are connected to the hull through operating levers, whereby the front leg may be pivoted left or right with respect to a central longitudinal axis of the hull, by movement of the operating links.

Preferably the front leg is connected to the hull through a parallelogram linkage.

Preferably the hull is provided with left and right outrigger hulls each with a balance leg.

Preferably each balance leg is understood as being a hydrofoil leg. Preferably each outrigger hull has a front leg and a side leg.

Preferably the front leg is a lift leg and the side leg is a balance leg.

Preferably each outrigger hull is pivotally connected with a cross arm of the main hull.

Preferably the third link pivotally connects one end of the cross arm to an upper end of the first link.

The lower end of the first link is preferably - o - connected to the first leg.

The lower end of the first link is preferably pivotally connected to a front part of the outrigger hull. A rear end of the outrigger hull is preferably pivotally connected to a lower part of one end of the cross arm and an upper part of one end of the cross arm is pivotally connected to the end of the third link opposite to the first link. Preferably the front leg is shorter than the back leg.

Preferably the distance between front and rear legs and the number of fins on each leg is chosen to ensure that for predetermined wind conditions the vehicle will not tip over in water.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1A shows a catamaran in accordance with the present invention;

Figure IB shows a trimaran in accordance with the present invention;

Figure 2 shows a first embodiment of a control system of the present invention when connected to an out rigger hull;

Figure 3 shows a plan view of the control system of figure 2;

Figure 4 shows a front view of the control system and outrigger hull of figure 2; Figure 5 shows a side view of a second embodiment of the control system of the present invention;

Figure 6 shows a side view of a third embodiment of a control system of the present invention; Figure 7 shows a plan view of the control system of figure 6;

Figure 8 shows a front cross-sectional view AA of the control system of figure 6; Figure 9 shows a front cross-sectional view BB of the control system shown in figure 6;

Figure 10 shows a fourth embodiment of the control system of the present invention; Figure 11A, 11B and 11C show a schematic view of the second control system shown in figure 2 for positive, zero and negative lift conditions respec ively;

Figure 12 shows a schematic front view of a trimaran; The main difference between the catamaran and trimaran shown in figures 1A and IB lies in the provision of one sail on the main body of the boat for the catamaran and the provision of two sails each on out rigger hulls for the trimaran. The rigging for both boats is also different according to the requirements of the sail or sails. The other features of both boats however, are almost identical.

Referring to the catamaran, a main hull 10 is provided with left and right outriggers 11 and 12 respectively connected to the main hull 10 through left and right outrigger arms 13, 14. The main hull 10 is provided with a front hydrofoil leg 15 which is steerable by virtue of a parallel linkage 16 which is connected to the ^' top of the front leg 15 on left and right sides respectively of cross member 17 and extends to a central part of the boat hull somewhere below the main mast 18 where its operation can be controlled by the legs of a person seated in a cabin 19 located at the rear of the boat. The linkage 16 operates in a horizontal plane and is controlled by moving the link 20 which connects left and right side links 21, 22 at the opposite end to cross- member 17.

The front leg is provided with two hydrofoil fins 23, 24 each extending on left and right sides of the leg and located at the bottom of the leg and just below the mid point of the leg respectively. Each of the fins are intended to have an NACA symmetrical profile as would be found in the wing of an aircraft. The lower most fin 23 is arranged to apply a downlift force to the leg and the fin 24 is an uplift fin which is arranged to apply an upwardly directed hydrodynamic force to the leg 15.

Both of the outrigger hulls comprise the same features namely, a front hydrofoil leg 25 and a rear hydrofoil leg 26. The front leg 25 is pivotally connected to the outrigger hull 12 at pivot point 27. It is also connected to a link 28 which forms part of a parallelogram linkage 29 which is effectively oriented in a vertical plane. Details of this parallelogram linkage 29 will be discussed in more detail later.

As previously mentioned, the trimaran 30 shown in figure IB has effectively the same features on both the outrigger hulls 31 , 32 and the front of the hull 30. The outrigger hull 30 will now be discussed in more detail with reference to figures 2 to 5. The difference between this outrigger and the outrigger 12 is only minor and is mainly as a result of the particular requirements of a trimaran as opposed to a catamaran. Referring to figure 2, an outrigger 40 is shown having a front leg 41 and rear leg 42. The front leg 41 is preferably angled forward at 10° with respect to a vertical axis and is provided with a downlift fin 43 at its lower most point and three uplift fins 44, 45, 46 equally spaced around the middle third part of the leg. The front leg is angled at approximately 10° with respect to a vertical axis and each of the fins have an NACA symmetrical profile with an angle of incidence of preferably between 3° and 8° with respect to the direction of motion of the craft.

Each of the fins are parallel and the difference between the uplift and downlift fins lies in the profile.

The downlift fin is effectively and upside down version of the uplift fin but has a negative angle of incidence with respect to the direction of motion.

The back leg 42 is oriented at approximately 8° with respect to a vertical axis but in contrast to the front leg, is angled away from the front of the boat. At the bottom of the back leg is a fin 47 which is angled to have a 0° angle of incidence with respect to the direction of motion of the craft.

The top of the front leg is pivotally connected to the front of the craft through pivot 48. In addition, an arcuate slot 49a is provided near the very top of the leg and in this slot a pin 49b is provided which is connected to link 50 which itself is pivotally connected between pivot 48 and an upper pivot 51. In the drawing this link is shown in a vertical orientation although it is able to move from this vertical orientation.

The upper pivot 51 is located on the end of link 52 which extends from the front of the outrigger hull 40 to the rear of the outrigger hull where it is pivotally connected through a pivot 54 to outrigger arm 55. The length of the link 52 may be changed by a trun buckle 53.

The outrigger arm 55 as well as being pivotally connected to the length 52, is also pivotally connected to the rear end of the hull through a pivot 56 which is aligned vertically with the centre of the outrigger arm 55 and the pivot 54. A damper 57 is connected from just in front of the pivot 56 to the link 52 just behind turn buckle 53.

As shown in figure 3, the link 52 runs parallel to a central longitudinal axis of the outrigger hull 40 and as shown in figure 4, the front leg 41 is also aligned with this central longitudinal axis while the rear leg 42 is displaced laterally to the left hand side of this central longitudinal axis. Referring to figure 5, the embodiment shown therein is similar to that shown in figure 2, the main difference however, is that the outrigger is reversed so that its intended direction of motion is the reverse of that shown in figure 2. The principle of operation of the control system represented by the parallelogram formed by the linkages between pivots 48, 51, 54 and 56, is effectively the same.

Referring now to the control system shown in - 12 - figure 6, as with that shown in figure 5, the components of the outrigger hull 40 are effectively the same as that shown in figure 2. The major difference is however, that instead of the hull 40 being one of the linkages in the parallelogram linkage defined by pivots 48, 50, 54 and 56, a separate linkage 60 is provided to interconnect pivot points 48 and 56. In addition, the location of the outrigger arm 55 is changed so that it is fixed to the rear end of the outrigger hull 40. Thus, the pivot 54 is also pivotally connected to the outrigger hull 40 and is still vertically aligned with the pivot 56.

The pivot 48 is still pivotally connected to link 49B and leg 41 but is no longer pivotally connected to the hull 40. The damper 57 instead of being connected to a rear part of the hull and to a point just behind turn buckle 53. on link 52, is connected at a midpoint of linkage 60 to a rear end of link 52.

The method of control provided by the parallelogram linkage shown in figure 6 is effectively the same as that shown in figure 2. The method of operation is slightly different because, in figure 2 the hull 40 which links pivots 48 and 56 is intended to be maintained in a substantially horizontal plane to ensure a comfortable ride for a person seated in the cabin of the main hull. In contrast, linkage 60 which links pivots 48 and 56 in figure 6, is able to move with link 52 about pivots 56 and 54 respectively to enable the front leg 41 to move up and down independently of the outrigger hull 40. The exact method of operation of the controlling system will be described with reference to figures 11A to 11C which show the controlling system of figure 2 in different situations.

Initially, when the watercraft with two outrigger hulls as shown in figure 11A, is placed in water, the outrigger hulls 40 act as a float which provides stability for the main hull. As the main hull moves forward, hydrofoil fins L2, L3 and L4 provide an upwardly directed force due to their shape and the fact that they are oriented with a positive angle of incidence θ with respect to the direction of motion. The lower most fin LI because of its shape and the fact that it has a negative angle of incidence - θ with respect to the direction of motion, provides a downwardly directed force. The result is that the upwardly directed force applied by fins L2 to L4 is greater than that applied by the downwardly directed force of LI. Consequently, the front leg is forced upwardly thus forcing up the front of the hull 40.

Consequently, the fin L5 on the rear leg is orientated from a zero angle of incidence with respect to the direction of motion to a positive angle of incidence represented by φ as shown in figure 11C. Thus, whereas initially the fin L5 of the rear leg provides no lift at all, because of its positive angle incidence φ, it provides an upwardly directed force on the rear leg which force is transferred to the rear of the outrigger hull consequently counter balancing the force applied by fins L2 to L4 of the front leg.

Depending on the speed of the watercraft, the front leg assumes a position whereby the upwardly directed force applied by fins L2 to L4 minus the downwardly directed force applied by fin LI effectively equals the downwardly applied force due to the weight of the outrigger hull 40. For a particular speed of the watercraft, this may occur when one of the fins L4 or two fins L4 and L3 are above the surface of the water. When such an equilibrium position is reached, this is called the hydrodynamic centre of the front leg. At the same time the rear leg will not lift any further out of the water because the angle of incidence of the fin L5 is reduced to zero once the hull 40 has assumed its original horizontal orientation.

If the speed of the watercraft increases, the upwardly directed hydrodynamic force applied by fin L2 in figure 11C will increase, thus lifting the front leg higher and at the same time, the rear leg is lifted to counter balance this lift applied to the front of the outrigger hull 40 in the same manner as previously described. Depending on the size and shape of the fins, it may be possible for fin L2 to be lifted out of the water. However, if this occurs, then the downwardly directed force applied by the fin Ll in conjunction with the weight of the hull 40 will automatically force the front leg downwardly and the fin L2 below the surface of the water. Thus, if the fin L2 is designed so that it has a greater hydrodynamic uplifting force, than the downwardly directed hydrodynamic force applied by fin Ll, the fin L2 would effectively oscillate from just below the surface of the water to just above the surface of the water.

Accordingly, it can be seen that it is important to design the fins so that the hydrodynamic centre maintains at least one of the fins on the front leg below the surface of the water. Such a design requirement is not essential if a small oscillation in the position of the front of the hull 40 is not critical.

It should also be noted that the control system provided by the parallelogram linkage P, acts to minimise the above mentioned oscillations in the same manner it acts to counteract any moments applied about the watercraf .

For example, referring to figure 11B, when a moment Ml is applied about the front of the outrigger hull 40, the effect is to apply a downwardly directed force on the front leg 41. The result is that the front of the hull 40 pivots with respect to the front leg 41. Thus, the front leg 41 is maintained in the same position but the back of the outrigger hull 40 is now higher than the front of the outrigger hull 40. It follows therefore, that the fin L5 is provided with a negative angle of incidence - φ which results in the fin L5 applying a downwardly directed force on leg 42 and on the rear end of the outrigger hull 40. Consequently, the hull 40 reassumes its horizontal configuration despit the presence of the moment Ml. If the front leg 41 was not connected through the parallelogram P, the front le 41 would also be forced downwardly resulting in the watercraft having an oscillation dependent on the speed of the watercraft and the amount of moment Ml applied to the front of the outrigger hull 40. However, with the parallelogram P acting as a control system a person seated in a cabin of the main hull would merely pivot with respect to the pivot point 48 and the front leg 41 connected thereto. Thus, there would be no oscillations or vibrations merely a slight pivoting depending on the magnitude of the moment Ml. If the moment Ml is particularly strong then the hydrodynamic centre would be initially changed to a higher position on legs 41 and 42. Referring to figure 11C, if a moment M2 is applied to the front of the outrigger hull 40 to lift it out of the water, the parallelogram linkage P again maintains the front leg 41 in the same orientation as shown in figures 11A and 11B. Instead, the front of the hull pivots upwardly with respect to the front leg 41, thus changing the fin L5 of the rear leg 42 to a positive angle of incidence φ . This results in an upwardly directed force which lifts the rear end of the outrigger hull 40 back to its horizontal orientation. Thus, again counter balancing the moment M2.

If follows from the above description that no matter what moment is applied to the watercraft or components thereof, the parallelogram linkage P acts as a controlling system to urge the outrigger hulls (in this example) back to a horizontal orientation. Likewise, the main hull is also returned to a horizontal orientation.

Operation of the control system of the first embodiment has been described with reference to figures 11A to 11C. However, the same principles apply to the other control systems. In each case, the parallelogram linkage serves to maintain the front leg in a constant orientation with respect to the direction of motion of - 16 - the watercraft.

In the embodiment shown in figure 6, the parallelogram linkage may be located inside the outrigger hull as is shown in figure 7. It is also noted that both the rear and front legs 41, 42 are aligned along the longitudinal central axis of the outrigger hull as shown in figures 8 and 9. This orientation is mainly provided to minimise stresses applied to the outrigger hull components. The outrigger hull shown schematically in figure

10 is effectively the same as that shown in figure 6 except the direction of motion of the outrigger hull of figure 10 is opposite to that shown in figure 6. However, the same principles of control as previously described still apply.

Referring to figure 12, an example is given of a trimaran having a wind force S applied to its sails. Using standard engineering design techniques, the moment applied about the trimaran is represented by M and = S x L\2 where L is the distance between the geometric centre of the sails measured vertically downwardly to the hydrodynamic centre of the hydrofoil legs (the legs having fins thereon) .

The lift applied to the trimaran can then be calculated using the following formula:

Lift = M/W ÷ 2 ± (g x f/2) where f equals a - 0.85 load factor for carriers at canard, g is the gravitational force and W is the distance between left and right hydrofoil legs. It is apparent that as long as the lift applied by the left hand hydrofoil leg is greater than the moment S x L/2, that the trimaran will remain in a stable horizontal configuration. The same also applies to the other hydrofoil leg. The embodiments shown in figures 1 to 12 are only given as an example to the possible applications of the present invention. It is quite possible however, to change the type of watercraft so that it is not merely a sailcraft but is a motorised watercraft. In addition, there is no restriction on the location of the hydrofoil leg or legs and it is possible to combine a single hydrofoil leg with stabilising floats.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A vehicle for use on water comprising a body part having a front leg and a back leg, one of the legs having downlift fin for applying a downwardly directed hydrodynamic force on the leg and at least one uplift fin for applying an upwardly directed hydrodynamic force on the leg, the other leg being a balance leg having a fin which is for applying an upwardly directed hydrodynamic force when at a positive angle of incidence with respect to a forward direction of motion of the vehicle and for applying a downwardly directed hydrodynamic force when at a negative angle of incidence with respect to the forward direction of motion, wherein the downlift fin prevents the one leg from lifting out of the water. 2. A vehicle as claimed in claim 1 wherein the one leg is oriented with respect to the intended forward direction of motion so that the downlift fin is always provided with a negative angle of incidence with respect to the forward direction of motion. 3. A vehicle according to any one of the preceding claims wherein the body part comprises an additional back or front leg.

4. A vehicle according to any one of the preceding claims wherein the front leg has downlift and uplift fins.

5. A vehicle according to any one of the preceding claims wherein the body part comprises left and right side body parts with back legs respectively being attached thereto. 6. A vehicle as claimed in claim 5 wherein the body part is the hull of a boat and the left and right side body parts are outrigger hulls.

7. A vehicle according to any one of the preceding claims wherein the fins are each in form of an NACA symmetrical profile.

9. A vehicle according to claim 8 wherein the lift leg is located at a front portion of the body part.

10. A vehicle according to claim 9 wherein the lift leg is provided with two or more uplift fins and one downlift fin.

11. A vehicle according to 10 wherein each uplift fin is evenly spaced apart from an adjacent uplift fin.

12. A vehicle according to claim 10 wherein the lift leg is pivotable with respect to the body part.

13. A vehicle according to claim 12 wherein the lift leg is automatically pivoted to a predetermined position with respect to the forward direction and dependent upon the speed of the vehicle.

14. A vehicle according to claim 13 wherein the fins are maintained at a predetermined orientation with respect to the direction of motion of the vehicle by a controlling means, the predetermined orientation enabling each fin to provide a maximum level of hydrodynamic force.

15. A vehicle as claimed in claim 12 wherein the fins of the lift leg are maintained at a predetermined orientation with respect to the direction of motion of the vehicle by a controlling means, the predetermined orientation enabling each fin to provide a maximum level of hydrodynamic force.

16. A vehicle as claimed in claim 15 wherein the uplift fins of the lift leg are maintain at a positive angle of incidence with respect to the direction of motion and the downlift fin is maintained at a negative angle of incidence with respect to the direction of motion, by the controlling means. 17. A vehicle according to claim 16 wherein the controlling means comprises a parallelogram linkage which at one end is pivotally connected to the body part and at the other end is pivotally connected to the lift leg. 18. A controlling system for a watercraft comprising a parallelogram linkage having front and rear ends, the front end being arranged to be pivotally connected to a front hydrofoil leg and the rear end being arranged to be connected with a rear hydrofoil leg, whereby in use the parallelogram linkage is arranged to maintain one of the legs in a predetermined orientation with respect to the direction of motion of the watercraft.

19. A controlling system as claimed in claim 18 wherein the parallelogram linkage acts to bias the watercraft to an equilibrium position when the watercraft is in motion. 20. A controlling system as claimed in claim 18 or 19 wherein one of the links of the parallelogram linkage is formed by part of the watercraft.

21. A controlling system as claimed in claim

20 wherein the one of the legs is fixed to one of the links of the parallelogram which is pivotable with respect to the watercraft.

22. A controlling system as claimed in claim

21 wherein the parallelogram linkage comprises two elongate links which are arranged to extend from a front end of the watercraft to a rear end of the watercraft, where they are pivotally connected together through front and rear links respectively.

23. A controlling system as claimed in claim

22 wherein the parallelogram linkage comprises two short links which pivotally connect the elongate links together.

24. A controlling system as claimed in claim

23 wherein the or each other hydrofoil leg is fixed to a part of the watercraft. 25. A controlling system as claimed in claim 23 or 24 wherein one of the hydrofoil legs comprises at least one uplift fin and at least one downlift fin, the uplift force provided by the uplift fin being greater than that provided by the downlift fin, and wherein the or each other leg comprises a fin which is arranged to be oriented at a 0° angle of incidence with respect to the direction of motion of the watercraft, when the watercraft is in the predetermined orientation. 26. A controlling system as claimed in claim 25 wherein the or each fin of the other leg provides an uplifting force when at a positive angle of incidence with respect to the direction of motion of the watercraft and provides a downlift force when at a negative angle of incidence with respect to the direction of motion of the watercraft.

SUBSTITUTESHEET