GB1581627A - Device to reduce the lowering and retraction resistance of hydrofoils - Google Patents

Description

(54) A DEVICE TO REDUCE THE LOWERING AND RETRACTION RESISTANCE OF HYDROFOILS (71) I, JOHN GRAHAM WALKER formerly of Ayias Lavros 10, Ano Glyfada, Greece now of 14 Winchmore Drive, Trumptupton, Cambridgeshire, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to hydrofoils, and in particular to retractable hydrofoils.

When hydrofoils are withdrawn from the water a considerable resistance may occur due to turbulence caused by changes in the angle of incidence of the hydrofoil to the water.

Accordingly the invention provides a hydrofoil which is pivotally supported at a position upstream from its centre of pressure on a strut which is movable to a position in which a portion of the hydrofoil abuts the strut so that the resultant force due to incident flow on the hydrofoil is transmitted to the strut, and when the strut is moved away from that position the abutting portion of the hydrofoil moves away from the strut. The strut may be rotatable from said position so that when the butting portion of the hydrofoil moves out of contact with the strut the hydrofoil pivots under the influence of the flow to take the position of minimum resistance.

The centre of pressure of a hydrofoil is the point at which, when the hydrofoil is working, all the lines of force may be assumed to act.

Depending on the angle of incidence of the flow to the hydrofoil the precise location of the centre of pressure may vary, but herein the term "centre of pressure" should be construed to include the range of possible precise locations.

In a preferred embodiment of the invention the hydrofoil may, when fully immersed and abutting the strut, provide lift to the strut and an associated craft. An adjustable stop may be provided on the strut against which a portion of the hydrofoil abuts, and the angle of incidence of the hydrofoil may be determined by the extent of projection of the stop.

The invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 illustates turbulence arising from withdrawal of a fixedly mounted hydrofoil, and Figure 2 illustrates an embodiment of the invntion.

In Figure 1 a hydrofoil A is mounted in a fixed position on an end of a supporting strut B which, in the position shown generally by reference 1, extends downwardly into the water to fully immerse the hydrofoil A. When the hydrofoil is not operatively required it can be retracted to the position shown generally as 3 by afterward rotation of the strut B. At intermediate positions occurring during insertion or withdrawal, one of which is shown generally as 2, the hydrofoil presents a large resistance, the large changes in angle of incidence of the hydrofoil and its generally unfavourable disposition causing stalling, flow breakaway, and turbulence, indicated generally at C. This resistance is particularly undesirable in vessels where transition from a low speed mode to a hgiher speed mode need to be made with the minimum of transitional water resistance.

In the embodiment of the invention shown in Figure 2 a hydrofoil A is pivotally mounted on a strut B by a pivot D adjacent the leading or upstream edge of the hydrofoil. The pivot D extends spanwise of the hydrofoil and, although illustrated at the leading edge of the hydrofoil, it may be positioned anywhere upsteam of the centre of pressure. When the strut B of Figure 2 is in an intermediate position such as 2 the hydrofoil is free to rotate about pivot D to a position of minimum resistance, until the strut B reaches its downward position 1, where upon the trailing edge of the hydrofoil abuts against a stop E on the strut B which holds down the trailing edge thereby increasing the angle of incidence and enabling the hydrofoil to provide (in this embodiment) a lift force which is transmitted to the strut.The stop E is connected to the strut B by a screw F which is adjustable to alter the angle of incidence of the hydrofoil A.

The screw may be remote controlled by a rod passing through the strut B. A further stop G is also provided on the hydrofoil A or on the pivot D which limits the maximum angle of freedom of the hydrofoil to the position shown at 3 in Figure 2.

In this embodiment a fully immersed hydrofoil is shown which provides a lift force. A surface piercing hydrofoil, i.e. one which does not fully submerge, may also be similarly mounted.

WHAT I CLAIM IS: 1. A hydrofoil which is pivotally supported at a position upstream from its centre of pressure on a strut which is movable to a position in which a portion of the hydrofoil abuts the strut so that the resultant force due to incident flow on the hydrofoil is transmitted to the strut, and when the strut is moved away from that position the abutting portion of the hydrofoil moves away from the strut.

2. A hydrofoil according to claim 1 in which the strut is rotatable from the said position so that when the abutting portion of the hydrofoil moves out of contact with the strut the hydrofoil pivots under the influence of the flow to take the position of minimum resistance.

3. A hydrofoil according to any preceding claim in which a stop is provided on the strut and the abutting portion of the hydrofoil abuts against the stop.

4. A hydrofoil according to claim 3 in which the stop is adjustable.

5. A hydrofoil according to claim 4 in which the stop may be adjusted by remote control via a rod passing through the strut.

6. A hydrofoil according to claim 4 or claim 5 in which the stop comprises a screw thread.

7. A hydrofoil according to any preceding claim in which a further stop is provided which limits the movement of the abutting portion of the hydrofoil away from the strut.

8. A hydrofoil substantially as hereinbefore described with reference to and as illustated in Figure 2 of the accompanying drawings.

9. A hydrofoil craft with one or more hydrofoils according to any preceding claim.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. pivot D which limits the maximum angle of freedom of the hydrofoil to the position shown at 3 in Figure 2. In this embodiment a fully immersed hydrofoil is shown which provides a lift force. A surface piercing hydrofoil, i.e. one which does not fully submerge, may also be similarly mounted. WHAT I CLAIM IS:

1. A hydrofoil which is pivotally supported at a position upstream from its centre of pressure on a strut which is movable to a position in which a portion of the hydrofoil abuts the strut so that the resultant force due to incident flow on the hydrofoil is transmitted to the strut, and when the strut is moved away from that position the abutting portion of the hydrofoil moves away from the strut.

2. A hydrofoil according to claim 1 in which the strut is rotatable from the said position so that when the abutting portion of the hydrofoil moves out of contact with the strut the hydrofoil pivots under the influence of the flow to take the position of minimum resistance.

3. A hydrofoil according to any preceding claim in which a stop is provided on the strut and the abutting portion of the hydrofoil abuts against the stop.

4. A hydrofoil according to claim 3 in which the stop is adjustable.

5. A hydrofoil according to claim 4 in which the stop may be adjusted by remote control via a rod passing through the strut.

6. A hydrofoil according to claim 4 or claim 5 in which the stop comprises a screw thread.

7. A hydrofoil according to any preceding claim in which a further stop is provided which limits the movement of the abutting portion of the hydrofoil away from the strut.

8. A hydrofoil substantially as hereinbefore described with reference to and as illustated in Figure 2 of the accompanying drawings.

9. A hydrofoil craft with one or more hydrofoils according to any preceding claim.