AU686860B2

AU686860B2 - A vehicle for use on water

Info

Publication number: AU686860B2
Application number: AU31761/95A
Authority: AU
Inventors: Michael Baranski
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-11-14
Filing date: 1995-09-19
Publication date: 1998-02-12
Anticipated expiration: 2012-11-09
Also published as: AU3176195A

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT .~r 4 a Invention Title: "A Vehicle For Use On Water" The following statement is a full description of this invention, including the best method of performing it known to us: GH&CO REF: P22487-C/RPW:AHS L I -I L- 14_L-- 2 A VEHICLE FOR USE ON WATER The present invention is particularly relevant to sailcraft and is also relevant to hydrofoil water-craft.

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

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

In 1972 C. Hooks came up with the idea of adjusting the foil angle of incidence with respect to the direction of motion of a craft, in an attempt to gain hydrofoil craft rolling stability where hydroblades are controlled by canard displaced buoyant bodies which act as water level sensors for input to a mechanical control system. Unfortunately, the mechanical control system required complex hydraulic and electrical controls which 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 eeoaw: conditions and suffered from sever high frequency vibration with increasing speed of the craft.

The present invention provides a controlling system on a watercraft that has a body portion, with front and rear S" hydrofoil legs being mounted to the body portion so that the body portion fully extends from the front leg to rear leg, the system comprising a parallelogram linkage having front and rear ends, the front end being adapted for pivotal S 30 connection to the front hydrofoil leg of the watercraft and the rear end being adapted for connection with the rear hydrofoil leg of the watercraft, wherein in use the parallelogram linkage is adapted for regulating the alignment or inclination of one of the legs with respect to vertical.

Spec: 22487C 2A Preferably in use the parallelogram linkage can be adjusted to bias the watercraft to an equilibrium position when the watercraft is in motion. Preferably, one of the links of the parallelogram linkage is formed by part of the watercraft. In this regard, it is I i I ~PI 3 preferred that one of the legs is fixed to one of the links of the parallelogram, which leg is pivotable with respect to the watercraft.

Preferably this one leg is pivotally mounted to the part of the watercraft at a lower vertex of the parallelogram linkage.

Preferably 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.

Preferably the front and rear links comprise two short links which pivotally connect the elongate links together.

In this regard the or each other hydrofoil leg can be fixedly mounted to a part of the watercraft.

Preferably 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 00 angle of incidence with respect to the direction of motion of the watercraft, when the watercraft is in the equilibrium position. In this regard the or each fin of the or each other leg can provide an uplift force when at a positive 25 angle of incidence with respect to the direction of motion I: of the watercraft and can provide a downlift force when at a negative angle of incidence with respect to the direction of motion of the watercraft.

Also disclosed herein is a vehicle for use on water comprising a body part and at least one lift 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 whereby in use, the lift leg is prevented from lifting A completely out of water as the vehicle moves on water, by

I

3A the cownlift, fin.

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4 The body part can comprise 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. The downlift fin can be located on a lower part of the lift leg. All uplift fins can be located above the one downlift fin.

Also disclosed herein is a vehicle 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 mounted thereto in an in use fixed orientation, the fin being for applying an upwardly directed hydrodynamic force when at a positive angle of 2 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 configuration of the one leg and the other leg is such that in use for either an upwardly or downwardly 25 directed force on either of the legs, a correspondingly directed force is imparted to the remaining leg to substantially restore the body part to an equilibrium position.

The downlift fin can prevent said one leg from lifting out of the water. The balance leg can be the ncn-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 S:22487C/1 8.9.95 of motion. The front leg may be the one leg.

The body part can comprise an additional back or front leg. If there is an additional back leg, in some variations 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. The vehicle can be 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.

The body part can be the hull of a boat. The left and right body parts may be outriggers. The height of the sails can be determined by the height of each balance leg and the distance from the ceaitral hull and one outrigger hull.

The uplift fin or fins can be angled at no greater than 300 with respect to the direction of motion of the rehicle. All uplift fins can be 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 o. 25 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.

The lift leg can 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 can be evenly spaced apart from an adjacent uplift fin.

S:22487C/18.9.95 I 6 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 can extend 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.

Both legs can be fixed but the fins can be 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 can comprise 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 the parallelogram linkage with the lift leg connected to a first link of 20 the linkage. The parallelogram linkage can comprise two o• pairs of parallel links pivotally connected together so that each pair of links may be moved with respect to the other pair of links. The first link can be located at one end of the parallelogram linkage.

25 Second and third links of the parallelogram linkage can be arranged to be parallel and maintained in a substantially horizontal configuration.

The body part can comprise left and right arms each having a non-lift leg. Each of the right and left arms can have a lift leg. All legs can be lift legs. Each lift leg may be angled forward of a vertical axis.

Each non-lift leg can be 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.

The lift leg when located at the front of the parallelogram linkage can be pivotable about one of the pivots and is slidably connected to the first link. The S:22487C118.9.95 -I .p -7lift leg :an be the front leg and can be pivoted to the pivot connecting the first and second links. The second link can be lower than the third link. A fourth link can be 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 t.he first link and a fourth pivot connected to the body part above the second pivot.

The second pivot can be connected to the hull of a boat. The third pivot may be connected to an outrigger arm of the hull. The outrigger arm of the hull can be pivntally connected through the fourth link to thF hull.

The fins can be arranged in parallel.

oe.o.i 20 The second and third links can be connected together by a damping means. The second and third links preferably can be connected together through a stiffening means arranged to limit load carried by the first and fourth pivots. Each of the pivots can be arranged to 25 extend in a horizontal axis perpendicular to the oo •direction of motion of the vehicle. The links may extend in the direction of motion of the vehicle.

The or each non-lift leg can be pivotable about a pivot extending horizontally in the direction of motion of the vehicle ie. from the front to the rear of the vehicle. The length of the second and third links may be different. The lengths of the legs can be different. A fourth link can be 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 can be 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 S:22487C/1 8.9.95 I~llils ~L~ 8 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. The vehicle can comprise a main hull with a front leg and left and right side legs. The left and right side legs can be located at the rear of the hull.

The front leg can be the lift leg and the left and right side legs can be balance legs.

The front leg can be steered by a person seated in the hull. The front leg can comprise 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 oeoeo: S 20 of the hull, by movement of the operating links. The front leg can be connected to the hull through a parallelogram linkage.

The hull can be provided with left and right outrigger hulls each with a balance leg. Each balance leg can be understood as being a hydrofoil leg. Each outrigger hull can have a front leg and a side leg. The front leg can be a lift leg and the side leg can be a balance leg. Each outrigger hull can be pivotally connected with a cross arm of the main hull. The third link can pivotally connect one end of the cross arm to an upper end of the first link. The lower end of the first link can be connected to the first leg. The lower end of the first link can be pivotally connected to a front part of the outrigger hull. A rear end of the outrigger hull can be 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. The front leg can be shorter S:22487C118.9.95 9 than the back leg. The distance between front and rear legs and the number of fins on each leg c.n be 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 re'erence to the accompanying drawings in which: Figure 1A shows a catamaran in accordance with the present invention; Figure lB 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 outri-er 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; e: S"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 respectively; Figure 12 shows a schematic front view of a trimaran; The main difference between the catamaran and trimaran shown in figures 1A and lB lies in the provision of one sail on the main body of the boat for the S: 22487C/18.9.95 10 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 l.eft and right side links 21, 22 at the opposite end to crossmember 17.

The front leg is provided with two hydrofoil fins 23, 24 each extending on left and right sides of the leg .eoooi 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 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

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2 2487C/18 9.95 I Ira 'le P II 11 figure 1B has effectively the same features oil 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 100 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 100 with ct to a vertical axis and each of the fins have NACA symmetrical profile with an angle of incidence of preferably between 30 and 80 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 80 with respect to a vertical axis but in contrast to the front Sleg, 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 00 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 fr:n this vertical orientation.

The upper pivot 51 is located on the end of link 52 S:22487C/18.9.95 0 12 which extends from the front of the outrigger hull 40 to the rear of Lhe 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 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 41 similar to that shown in figure 2, the main difference 20 however, is that the outrigger is reversed so that its oeeoe S"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 S" linkages between pivots 48, 51, 54 and 56, is effectively the same.

Referring now to the control system shown in figure ooe 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 g 30 instead of the hull 40 being one of the linkages in the 55.9 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 thiat 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 S:22487C118.9.95 13 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 lin. 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 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.

S.Initially, when the watercraft with two outrigger .oo.

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 8 with respect to the direction of motion. The lower most fin L1 because of its shape and the fact that it has a negative angle of incidence 0 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 L1. Consequently, the front leg is forced upwardly thus forcing up the front of the hull Consequently, the fin L5 on the rear leg is orientated from a zero angle of incidence with respect to S:22487C/118.9.95

I

14 the direction of motion to a positive angle of incideilce represented by 0 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 4, 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 L1 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 .eo.ei 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 e 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.

SHowever, if this occurs, then the downwardly directed force applied by the fin L1 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 L1, the fin L2 S:224877C/18.9.95 I ~-II 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 cn 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 watercraft.

For example, referring to figure lIB, when a moment M3. is applied about the front of the outrigger hull the effect is to apply a downwardly directed force on the front leg 41. The result is that the front of the hull pivots with respect to the front leg 41. Thus, the front leg 41 is maintained in tLe same position but the S 20 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 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 reassumes s horlzontal configuration despite the presence of the moment Mi. If the front leg 41 was not connected through the parallelogram P, the front leg 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 M1 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 MI. If the moment M1 is S:22487C/1 8.9.95

I

16 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 0. 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 Sembodiment has been described with reference to figures 11A to 1C. 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 the watercraft.

6go SIn 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 30 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 is effectively the same as that shown in figure 6 except the direction of motion of the outrigger hull of figure is opposite :o that shown in figure 6. However, the S:22487C118.9.95 17 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 S"other hydrofoil leg.

The embodiments shown in figures 1 to 12 are only ee 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, e. •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.

S:22487C/I /18.9.95

Claims

2. A controlling system as claimed in claim 1 wherein in use the parallelogram linkage can be adjusted to bias the watercraft to an equilibrium position when the watercraft is in motion. :o oe
3. A controlling system as claimed in claim I ur claim 2 ©wherein one of the links of the parallelogram linkage is S. formed by part of the watercraft.
4. A controlling system as claimed in any one of the i 25 preceding claims wherein one of the legs is fixed to one of the links of the parallelogram which leg is pivotable with respect to the watercraft.
5. A controlling system as claimed in claim 4 wherein the •o 30 one leg is pivotally mounted to the watercraft at a lower vertex of the parallelogram linkage.
6. A controlling system as claimed in claim 4 or claim wherein the other hydrofoil leg is fixedly mounted to a part of the watercraft. rN 19
7. A controlling system as claimed in claim 1 or claim 2 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.
8. A controlling system as claimed in claim 7 wherein the front and rear links comprise two short links which pivotally connect the elongate links together.
9. A controlling system as claimed in any one of the preceding claims 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 other leg comprises a fin which is arranged to be oriented at a 00 angle of incidence with respect to the direction of motion of the watercraft, when the watercraft is in the equilibrium position.
10. A controlling system as claimed in claim 9 wherein the or each fin of the other leg provides an uplift force when at a positive angle of incidence with respect to the 25 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.
11. A controlling system on a watercraft substantially as herein described with reference to the accompanying drawings. Dated this 10th day of July 1997 Michael Baranski By their Patent Attorneys GRIFFITH HACK Nu ABSTRACT A controlling system for a watercraft is defined. The system comprises a parallelogram linkage having front and rear ends. The front end is arranged to be pivotally connected to a front hydrofoil leg and the rear end is arranged to be connected with a rear hydrofoil leg. In use, the parallelogram linkage is adapted for regulating the alignment or inclination of one of the legs with respect to vertical. S S 0* 4 ea S:22487C/18.9.95