Retractable foil mechanism

1. A retractable foil mechanism comprising:

a foil arranged to extend substantially parallel to a first axis when in a retracted position;

a rotation axis about which the foil can rotate;

an electrical and/or a mechanical actuator, or a hydraulic actuator or an electrohydrostatic actuator adapted to cause an acting force to act on the foil in a first direction parallel to the first axis; or a mechanism adapted to control a downward pull from the weight of the foil acting to pull the foil downwardly, so as to cause an acting force to act on the foil in a first direction parallel to the first axis, so as, in use, to move the foil and the rotation axis in the first direction; and

a moment creation arrangement configured such that, in use, the acting force on the foil creates a moment which causes the foil to rotate about the rotation axis while the rotation axis is moving in the first direction.

2. A retractable foil mechanism as claimed in claim 1 , wherein the moment creation arrangement comprises a guide member for engaging with a locating member linked to the foil, wherein the guide member extends at an angle to the first direction, such that, in use, the acting force causes a reaction force at the locating member, acting along a line perpendicular to the angle of the guide member, and the moment depends on the distance between the line of the reaction force and a parallel line through the rotation axis.

3. A retractable foil mechanism as claimed in claim 2 , wherein the angle at which the guide member extends relative to the first axis is varied along the extent thereof, to control the rate of rotation of the foil as the locating member travels along the guide member.

4. A retractable foil mechanism as claimed in claim 3 , wherein the guide member comprises a first portion which extends at a first angle to the first axis and a second portion extending beyond the first portion at a second angle to the first axis, wherein the second angle is greater than the first angle or wherein the guide member comprises a first portion which extends at a first angle to the first axis and a second portion extending beyond the first portion and towards the first axis.

5. A retractable foil mechanism as claimed in claim 4 , wherein the guide member further comprises a curved portion extending between the first portion and the second portion.

6. A retractable foil mechanism as claimed in claim 4 , wherein the first angle is in a range of 0° to 30° and/or wherein the second angle is in a range of 45° to 90° and/or wherein the guide member comprises a groove and/or wherein the locating member comprises one or more bearings or wheels.

7. A retractable foil mechanism as claimed in claim 2 wherein the moment creation arrangement comprises a plurality of guide members for engaging with a plurality of locating members linked to the foil, and wherein the plurality of guide members follow different paths so as to create different moments at least over a portion of the extent thereof.

8. A retractable foil mechanism as claimed in claim 2 , wherein the foil comprises:

a tip;

a root;

first and second surfaces extending between the tip and the root; and

first and second side edges joining the first and second surfaces at either side thereof, wherein a first locating member linked to the first side edge of the foil engages a first guide member and a second locating member linked to the second side edge of the foil engages a second guide member.

9. A retractable foil mechanism as claimed in claim 2 , further comprising:

a further guide member extending parallel to the first axis; and

a further locating member linked to the foil and movable along the further guide member.

10. A retractable foil mechanism as claimed in claim 9 , wherein the further locating member is centered on the rotation axis.

11. A retractable foil mechanism as claimed in claim 10 , wherein

a first further guide member and a first further locating member are provided adjacent a first side edge of the foil and a second further guide member and a second further locating member are provided adjacent a second side edge of the foil.

12. A retractable foil mechanism as claimed in claim 8 , wherein

the first guide member follows a first path and the second guide member follows a second path, wherein the second path is different from the first path such that the moment created by the first guide member is different to the moment created by the second guide member at least over a portion of the extent thereof.

13. A retractable foil mechanism as claimed in claim 2 , wherein the mechanism comprises two foils.

14. A retractable foil mechanism as claimed in claim 13 , wherein the foils share the rotation axis, and wherein the moment causes the foils to rotate away from each other in use and/or wherein the foils have roots configured to abut one another when the foils are in a deployed position.

15. A retractable foil mechanism as claimed in claim 2 , wherein the guide member is configured to create a moment to oppose forces acting to rotate the foil towards the first axis when the foil is in a deployed position.

16. A retractable foil mechanism as claimed in claim 15 , wherein the guide member comprises a portion extending at an angle of between 0° and 30° to the first direction at the lower extent thereof and the mechanism is configured such that the locating member is located within the portion when the foil(s) are in a deployed position.

17. A retractable foil mechanism as claimed in claim 16 , wherein the portion extends at an angle of between 0° and 10° to the first axis.

18. A retractable foil mechanism as claimed in claim 2 , further comprising a stop for limiting the movement of the rotation axis in the first direction, wherein the moment creation arrangement is configured such that, in use, the foil(s) rotate further about the rotation axis while the rotation axis is held against further movement by the stop.

19. A ship or vessel comprising:

a hull; and

a retractable foil mechanism as claimed in claim 2 , wherein the foil(s) is/are adapted to extend in a substantially vertical direction within the hull when in the retracted position and to extend externally of the hull and at an angle to the vertical when fully deployed.

20. A retractable foil mechanism comprising:

a foil arranged to extend substantially parallel to a first axis when in a retracted position;

a rotation axis about which the foil can rotate;

means for causing an acting force to act on the foil in a first direction parallel to the first axis so as, in use, to move the foil and the rotation axis in the first direction; and

a moment creation arrangement configured such that, in use, the acting force on the foil creates a moment which causes the foil to rotate about the rotation axis while the rotation axis is moving in the first direction, wherein the moment creation arrangement comprises a guide member for engaging with a locating member linked to the foil, wherein the guide member extends at an angle to the first direction, such that, in use, the acting force causes a reaction force at the locating member, acting along a line perpendicular to the angle of the guide member, and the moment depends on the distance between the line of the reaction force and a parallel line through the rotation axis.