IMPROVED KEEL

Abstract: An improved keel arrangement for sailing vessels, comprising a hydrofoil surface (10) mounted for rotation about an axis (4) parallel to the vessel's centreline and capable of producing a hydrodynamic lift force acting in a direction perpendicular to its axis (4) of rotation, the hydrofoil surface being selectively orientable to vary the direction of the lift force with respect to the vertical. Preferably two such hydrofoil surfacs (10L, 10W) are provided, so that their lift forces may be oriented to provide a net windward force and a righting moment to the vessel (3).

Description: The present invention relates to sailing vessels, and is particularly concerned with an improved keel apparatus for use in such vessels to reduce leeway and operable to provide a righting moment to counteract capsizing moments caused by lateral forces on the rigging. The keel apparatus may also be used to reduce the displacement of the vessel, thus reducing wavemaking resistance. Conventionally, sailing vessels have been provided with keels or leeboards to counteract leeway, the keel being ballasted to provide a righting moment when the vessel is heeled. In order to provide a lateral force to counteract leeway, the vessel moves forward in the water with a yaw angle giving the keel an "incidence" angle so that it acts as a hydrofoil surface giving lift directed laterally of the vessel. However, this action of the keel also produces drag. The present invention seeks to provide an apparatus which, when fitted to a vessel, can exert a lateral force and/or a rolling moment on the vessel as it moves forward through the water, or can be arranged to provide a vertically upward force to reduce the vessel's displacement. According to the present invention, a keel arrangement for simultaneously countering leeway and heeling in a sailing vessel or for reducing the displacement of the vessel provided with at least two hydrofoil surfaces spaced symmetrically from the vessel's centreline and mounted for rotation about axes extending parallel thereto, each hydrofoil surface being capable of exerting a hydrodynamic force directed perpendicularly to its axis of rotation, and the hydrofoil surfaces being independently angularly orientable about their respective rotation axes, characterised in that the hydrofoil surfaces are so oriented that: a) the leeward of the hydrofoil surfaces exerts a force having a windward and an upward component, and the windward hydrofoil surface exerts a force having a windward and a downward component or b) the leeward of the hydrofoil surfaces exerts a force having an upward component and the winward hydrofoil surface exerts a force having a pure windward component, or c) Both hydrofoils exert forces having an upward component. Preferably, each hydrofoil surface comprises a pair of fins arranged symmetrically about the rotation axis of the hydrofoil surface and at a predetermined incidence angle relative to the rotation axis. It is foreseen that the incidence angle of the hydrofoil surfaces may be made variable. The hydrofoil surfaces are preferably mounted to the vessel's hull by means of one or more pylons extending from the hull, each hydrofoil surface being rotatably mounted at the free end of a pylon or between the free ends of two pylons. The means for orienting each hydrofoil surface relative to the vertical advantageously comprises a shaft rotatably mounted within a pylon and carrying a bevel gear at its outboard end, the bevel gear meshing with a bevel gear fixed to the hydrofoil surface so that rotation of the shaft causes rotation of the hydrofoil surface about its axis. In a further aspect of the invention, control of a sailing vessel having the hydrofoil surfaces described above can be further improved by the use of a bow foil mounted on a single pylon beneath the forward part of the vessel. The pylon will preferably be of faired cross-section and will be rotatable about a vertical axis to serve as a rudder, possibly replacing the conventional stern rudder. A lifting foil surface mounted on the bow pylon assists in keeping the vessel's direction in conformity with the sea surface, thus reducing transient variations in incidence at the hydrofoil surfaces further aft. The incidence of the bow foil may be fixed or variable. An embodiment of the invention will now be described with reference to the accompanying drawings, in which, Figure 1 is a schematic perspective view of a hydrofoil surface and its supporting pylons; and Figures 2 to 4 are schematic views of a vessel fitted with two of the hydrofoil surfaces shown in Figure 1. Referring now to Figure 1, there is seen a pair of pylons 1, 2 which project downwardly from a vessel's hull 3 (only partially shown in the Figure). Extending between the free ends of the pylons 1 and 2 is a shaft 4, whose ends are received in bearings 5 and 6 in the pylons 1 and 2 for rotation about its axis. The shaft is arranged so that its axis is parallel to the centreline of the vessel, and is generally horizontal. At the forward end of the shaft 4 is mounted a bevel gear 7, which meshes with a cooperating gear 8 mounted to a control shaft 9. As is clear from the drawing, rotation of the shaft 9 will cause the shaft 4 to rotate by an amount corresponding to the gear ratio of gears 7 and 8. Mounted to the shaft 4 is a hydrofoil surface 10 comprising a pair of fins 11, 12 which are of a cambered foil section and are set at an angle relative to the shaft axis, so that as the vessel moves through the water then a hydrodynamic lift force is generated by the fins. The lift force is arranged to act in a direction perpendicular to the axis of the shaft 4. In a preferred installation, shown in Figures 2 to 4, a vessel's hull 3 is fitted with two hydrofoil surfaces 10L, 10W, spaced symmetrically about the vessel's centreline. Drive means (not shown) are provided within the hull 3 which can be operated to rotate the shafts 4 and hold them, and thus the hydrofoil surfaces 10L and 10W, in any desired angular position. Such drive means may be manual, for example a simple handwheel mounted on the shaft 9 at an accessible point within the vessel, or the drive means may be an electric motor or other remotely controllable drive. Transmission of the drive to the shaft 4 may be via a control shaft and bevel gears, or it may be achieved via a flexible coupling or universal joint, or the control shaft 9 may be replaced by a chain or other drive arrangement. Preferably, an indication of the angular orientation of the shafts is provided, either by marking the handwheels of manual drives and providing an electrical indication of the angular positions of the shafts 4 by means of electrical sensors acting on the control shafts 9 or the shafts 4 or on their drive trains and relaying position information to a display device. Operation of the apparatus is simple, in that the orientation of the lift forces produced by the hydrofoil surface is arranged, by rotating shafts 4 to desired positions, so as to provide a resultant force and/or moment acting on the vessel to counter the leeward forces and heeling moments produced by the wind in the rigging and sails. For example, in the vessel shown in Figure 2, the shafts 4 are separated by a distance b. Thus if each hydrofoil surface 10L, 10W exerts a lift force F (indicated by the arrow) at right angles to the shaft axis, then in the position shown in Figure 2 there is a resultant upward force of 2F tending to lift the vessel. This is useful when running before the wind, as the displacement of the hull is reduced, thus reducing drag. With the wind abeam indicated by arrow A, the vessel is subjected to a heeling moment due to the lateral force on the sails and rigging. By rotating the windward side hydrofoil surface 10W to an inverted position, its "lift" force F is arranged to act downwardly and thus the combined effect of the two hydrofoil surfaces 10L and 10W is a moment of Fb counteracting the heeling moment. Such an arrangement will not however provide any lateral force to counter leeway, and thus a position similar to Figure 3 will be adopted, wherein the leeward hydrofoil surface 10L is directed upwardly and inclined slightly to windward of the vertical, and the windward hydrofoil 10W is directed downwardly and inclined slightly to windward of the vertical, thus giving rise to a combination of a lateral force to windward and a righting moment. In the position shown In Figure 4, the leeward hydrofoil surface 10L is arranged to provide a vertically upward force, and the windward hydrofoil surface 10W is oriented to provide a substantially horizontal force to windward. This again will cause a righting moment and a force to counteract leeway. Clearly, the helmsman may select the combination of orientations for the two hydrofoil surfaces which best suits the point of sailing and wind strength at a given time. While it is preferred to install two hydrofoil surfaces 10L, 10W, it is possible to equip the vessel with a plurality of such surfaces. A further alternative is that each hydrofoil surface may be mounted to a single pylon. The hydrofoil surfaces may be of considerable weight, to have a ballasting effect, since rotation of a hydrofoil surface 10 will not move its centre of gravity and thus upset the vessel's trim.

Claims: A keel arrangement for simultaneously countering leeway and heeling in a sailing vessel or for reducing the displacement of the vessel, provided with at least two hydrofoil surfaces (10) spaced symmetrically from the vessel's centreline and mounted for rotation about axes extending parallel thereto, each hydrofoil surface being capable of exerting a hydrodynamic force directed perpendicularly to its axis of rotation, and the hydrofoil surfaces (10L, 10W) being independently angularly orientable about their respective rotation axes, characterised in that the hydrofoil surfaces are so oriented that: a) the leeward of the hydrofoil surfaces (10L) exerts a force having a windward and an upward component, and the winward hydrofoil surface (10W) exerts a force having a winward and a downward component, or b) the leeward of the hydrofoil surfaces (10L) exerts a force having an upward component and the winward hydrofoil surface (10W) exerts a force having a pure windward component, or c) Both hydrofoils (10L, 10W) exert forces having an upward component. An apparatus according to Claim 1, characterised in that each hydrofoil surface (10) comprises a pair of fins (11, 12) mounted for rotation about a chordal axis (4) passing through their roots and aligned parallel to the vessel's centreline. An apparatus according to Claim 2, characterised in that the means for mounting the respective hydrofoil surfaces (10) to the vessel are pylons (1) extending from the vessel's hull (3), the hydrofoil surfaces being pivotally mounted to the free ends of the pylons. An apparatus according to any preceding Claim, characterised in that each hydrofoil surface (10) comprises a shaft (4) and a pair of fins (11, 12) mounted thereto, the shaft being journalled at its respective ends in bearings (5) housed in the free ends of two pylons (1) extending from the vessel's hull (3). An apparatus according to Claim 3 or Claim 4, characterised in that the means for orienting each hydrofoil surface (7, 8, 9) comprises a drive means and a transmission coupling the drive means to the hydrofoil surface. An apparatus according to Claim 5, characterised in that the transmission comprises a rotating control shaft (9) and a pair of bevel gears (7, 8). An apparatus according to Claim 5, characterised in that the transmission comprises a chain and sprockets. An apparatus according to any of Claims 5 to 7, characterised in that the drive means is manually operated. An apparatus according to Claim 8, characterised in that the drive means is a handwheel or crank. An apparatus according to any of Claims 5 to 7, characterised in that the drive means is motorised. An apparatus according to Claim 10, characterised in that the drive means is an electric motor.

Inventors: JEFFREYS, PETER B.
Applicants: JEFFREYS, PETER B.
Application year: 1989
Main classification: B63B41
IPC codes: B63B41, B63B1