EP0373913A1

EP0373913A1 - Improved keel

Info

Publication number: EP0373913A1
Application number: EP89313029A
Authority: EP
Inventors: Peter B. Jeffreys
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-12-15
Filing date: 1989-12-13
Publication date: 1990-06-20
Anticipated expiration: 2009-12-13
Also published as: GB2226281B; DE68908860D1; GB8829293D0; EP0373913B1; GB2226281A; DE68908860T2

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, an improved keel for a sailing vessel comprises two hydrofoil surfaces mounted symmetrically about the vessel's centreline and capable of exerting on the vessel horizontal and vertical force components, the hydrofoil surfaces being independently orientable so that their combined effect is to exert either a net vertical force, a horizontal force or a rolling moment on the vessel, or a combination of two or more of such forces and moment.
According to a first embodiment of the present invention, an apparatus for exerting lateral force and/or rolling moment on a vessel moving forward through the water comprises one or more hydrofoil surfaces mounted to the hull of the vessel below the waterline for rotation about respective axes parallel to the vessel's centerline, the or each hydrofoil surface being so shaped as to produce a major hydrodynamic force component directed radially with respect to its rotation axis when moved through the water, and the apparatus further including means operable selectively to orient the direction of the hydrodynamic force of each hydrofoil surface in a desired direction relative to the vertical by rotating each hydrofoil surface about its respective axis.
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 second embodiment of the invention one or more pairs of hydrofoil surfaces are arranged beneath the hull of a sailing vessel symmetrically about the vessel's centreline, the hydrofoil surfaces being set at a dihedral angle, at least one pair of hydrofoil surfaces being rotatable about an axis transverse to the vessel to vary the angle of incidence of the hydrofoil surface.
Preferably in such an arrangement the hydrofoil surfaces are spaced from centreline, and this is achieved most advantageously by mounting a pair of hydrofoil surfaces to the end regions of the bilge keels of a sailing vessel, the hydrofoil surfaces extending outwardly and upwardly from the bilge keels. It is also foreseen that each bilge keel could carry hydrofoil surfaces extending outboard and extending inboard, and that the hydrofoil surfaces may be mounted slightly above the lower end of the bilge keel to provide clearance for beaching the vessel. In a further alternative, each bilge keel may carry a plurality of hydrofoil surfaces arranged in a vertical "stack" and linked to have their incidence angle vary in unison. Such an arrangement enables the required surface area of hydrofoil to be provided without extending outboard beyond the hull of the vessel, and thus avoiding problems of fouling jetties or other craft. In yet a further alternative, the aspect ratio of each hydrofoil surface may be improved by providing two hydrofoil surfaces of small chord mounted in tandem one behind the other, and controlled so that one or both surfaces may vary its angle of incidence.
It is further foreseen that the angle of incidence of the hydrofoil surfaces may be varied by rotating the entire bilge keel, the hydrofoil surfaces being firmly fixed to the bilge keel.
It is also foreseen that an existing vessel with bilge keels could be converted to operate the improved keel of the invention, by fitting to the vessel one or more pairs of hydrofoil surfaces and the associated control system for varying the incidence of the hydrofoils.
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.
Two embodiments of the invention will now be described with reference to the accompanying drawings, in which,

Figure 1 shows a first embodiment of the invention, and is a schematic perspective view of a hydrofoil surface and its supporting pylons.
Figures 2 to 4 are schematic views of a vessel fitted with two of the hydrofoil surfaces shown in Figure 1,
Figure 5 is a side view of a vessel equipped with an improved keel according to a second embodiment of the invention,
Figure 6 is a view of the vessel of Figure 5 from the bow,
Figure 7 is a schematic view of a control system for one of the hydrofoil surfaces shown in Figures 5 and 6,
Figure 8 is a view similar to Figure 5, showing an arrangement of two hydrofoil surfaces aft and a single bow foil, and
Figure 9 is a view from the bow of the vessel shown in Figure 8.

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 an 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 thelift 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.
A second embodiment of the invention is shown in Figures 5 and 6, wherein side and bow views of the hull of a bilge keel sailing vessel are shown.
The vessel 20 is of conventional layout in that two bilge keels 21P, 21S, project downwardly from the hull 22. Adjacent the lower edges of the bilge keels, a pair of hydrofoil surfaces 23P, 23S, extend outwardly and upwardly from their respective bilge keels 21P, 21S.
The hydrofoil surfaces are mounted for limited rotation about an axis extending laterally of the vessel, so that the angle of incidence of each hydrofoil surface may be varied to provide either a "positive" incidence or a "negative" incidence. Preferably the hydrofoil surfaces have an angular travel of some 10 to 15 degrees on each side of a zero incidence datum. By "positive" incidence is meant an angle of incidence giving rise to a generally upward hydrodynamic force on forward movement of the vessel, and by "negative" incidence is meant on angle of incidence giving rise to a generally downward hydrodynamic force on forward movement of the vessel.
Rotation of the hydrofoil surfaces to vary their incidence angles may be achieved by a mechanical linkage such as a chain or a bevel gear drive operating on a shaft pivotally mounted in the bilge keel and to which the hydrofoil surface is fixed; preferably, however the hydrofoil surface is mounted to the bilge keel for free pivotal movement about an axis passing slightly forward of its hydrodynamic centre and through its center of gravity. In this way, the hydrofoil surface will seek to adopt a zero incidence angle when the vessel moves. A control rod, connected to a point near the trailing edge of the hydrofoil surface may then be pushed down or pulled up to apply "positive" or "negative" incidence respectively.
Alternatively, cables connected to points positioned forward and aft of the pivot axis of the hydrofoil surface may be pulled to induce positive or negative incidence.
In a preferred control system shown schematically in Figure 7, a rod 24 is connected to the hydrofoil surface 23 adjacent its trailing edge, and the hydrofoil surface pivots freely about an axis X defined by a shaft mounted to the bilge keel. Control of the hydrofoil is achieved by threading the upper end 25 of the rod 24 and engaging the thread in a nut 26 fixed to the vessel's hull against axial displacement but with freedom to rotate. Rotation of the nut 26, either by manual or motorised means, will raise or lower the trailing edge of the hydrofoil surface 23 and thus apply negative or positive incidence respectively to the hydrofoil surface. Advantageously the axial position of the rod 24 relative to the vessel's hull is used as an indication of the incidence angle by attaching a scale 27 to the hull and a pointer 28 to the rod. A further advantageous feature of the system comprises means by which the rod may be allowed to "float" freely in the axial direction, thus allowing the hydrofoil surface to find a zero incidence position using a "weathercock" effect. This is achieved in the arrangement shown by mounting the nut 26 in a block 29 slidable along a track 30 and lockable at any point along the track 30 by means of a locking screw 31.
In operation, the hydrofoil surfaces 23 are controlled by means of rods 24 to generate upward or downward forces as required to resist rolling. It will be appreciated that, with the wind abeam and the windward hydrofoil surface set at negative incidence and the leeward hydrofoil surface set at positive incidence, a moment will be produced to counteract heeling. Furthermore, due to the dihedral angle between the hydrofoil surfaces, the hydrodynamic force vectors will both be inclined to the vertical to generate force components to windward, thus counteracting leeway.
When running before the wind, both hydrofoil surfaces will be set to positive incidence and the effect will be to reduce displacement and cut down resistance. Clearly, at low speed the displacement reduction due to the hydrodynamic effect may give a reduction in drag which is insufficient to compensate the hydrodynamic drag of the hydrofoil surface. In such cases the hydrofoil will be "featured" by releasing the locking screw 31 and allowing the hydrofoil surfaces to adopt a zero incidence position.
In Figures 8 and 9, a vessel 122 is shown fitted with a pair of bilge keels or pylons 121S, 121P, at the lower ends of which are situated outwardly extending dihedral foil surfaces 123S, 123P respectively. A bow foil 124 is mounted at the lower end of a vertical pylon 125 extending down from the forward part of the vessel's hull. A fin 126 extends below the bow foil 124, and the ends of the bow foil are fitted with vertical fences 127 extending above and below the foil surface.
The bow foil 124 may be of fixed incidence, in which case it will be set to generate upthrust, or may be of variable incidence to generate either upthrust or downthrust. The pylon 125 is mounted to the hull so as to be rotatable about a vertical axis, to act as a rudder either in combination with or in place of a conventional stern-hung rudder.
The presence of the bow foil has three main effects on the vessel's performance. Firstly, when moving in a heavy sea, the bow foil will cause the bow of the vessel to follow more closely the contour of the waves. This will substantially eliminate 'slamming', and will ensure that the hydrofoil surfaces 123P and 123S maintain a substantially constant angle of incidence relative to the water flowing over them.
Secondly, when running before the wind, the bow foil will be a deterrent to 'pitch poling', a manoeuvre in which the bow is forced down to submerge the foredeck and the vessel simply turns over about a transverse axis. The bow foil will effectively prevent the bow from burying itself into a sea.
Thirdly, the bow foil and pylon will support the vessel on a three-point 'undercarriage' when drying out on the bottom, so that the hull is stably held upright. To present a large area to support the vessel's weight on soft mud, the pylons 121P and 121S may be mounted for pivotal motion about their roots so as to bring the hydrofoil surfaces 123S and 123P into a horizontal plan for resting flat on the bottom, as shown in phantom lines at 'R' in Figure 9. This may also be a useful feature when berthing in a marina or against a harbour wall, as the hydrofoil surfaces will be retracted well under the hull preventing fouling on jetties, nearby craft, etc.
The fin 126 below the bow foil surface 124 is used when the vessel is planing with only the underside of foil 126 in contact with the water. The fin retains rudder control of the vessel at these speeds. The control of the hydrofoil surfaces may not be as complicated as has been shown, in that in the simplest systems the hydrofoil surfaces may have only three settings, viz positive, zero, and negative, to reduce cost, particularly in the case of retrofitted keel arrangements. In any case, an indication to the helmsman of the incidence angles of the foils at any given moment will be provided by means of a display.

Claims

1. An improved keel arrangement for a sailing vessel, comprising at leat two hydrofoil surfaces mounted symmetrically about an axis and capable of exerting horizontal and vertical force components, the hydrofoil surfaces being independently orientable so as to exert a nett vertical force, a horizontal force or a rolling moment on the vessel or a combination of two or all of such forces and moment.

2. An apparatus according to Claim 1, comprising a pair of hydrofoil surfaces mounted to the hull of the vessel for rotation about a rotation axis parallel to the vessel's centreline, the hydrofoil surface being shaped to produce a hydrodynamic lift force directed perpendicularly to its rotation axis, and the apparatus further including means operable to orient the hydrofoil surface in a selected angular position about its rotation axis.

3. An apparatus according to Claim 2, wherein the vessel is provided with two pairs of hydrofoil surfaces mounted for rotation about parallel rotation axes spaced symmetrically on either side of the vessel's centreline.

4. An apparatus according to Claim 2 or Claim 3, wherein the means for mounting the respective pairs of hydrofoil surface to the vessel is a pylon extending from the vessel's hull, the pair of hydrofoil surfaces being pivotally mounted to the free end of the pylon.

5. An apparatus according to any preceding Claim, wherein the or each pair of hydrofoil surfaces comprises a shaft and a pair of fins mounted thereto, the shaft being journalled at its respective ends in bearings housed in the free ends of two pylons extending from the vessel's hull.

6. An apparatus according to Claim 4 or Claim 5, wherein the means for orienting the hydrofoil surfaces comprises a drive means and a transmission coupling the drive means to the hydrofoil surface.

7. An apparatus according to Claim 6, wherein the transmission comprises a rotating control shaft and a pair of bevel gears.

8. An apparatus according to Claim 6, wherein the transmission comprises a chain and sprockets.

9. An apparatus according to any of Claims 6 to 8, wherein the drive means is manually operated.

10. An apparatus according to Claim 9, wherein the drive means is a handwheel or crank.

11. An apparatus according to any of Claim 6 to 8, wherein the drive means is motorised.

12. An apparatus according to Claim 11, wherein the drive means is an electric motor.

13. An improved keel arrangement according to Claim 1, wherein the pair of hydrofoil surfaces is constituted by two hydrofoil surfaces arranged beneath the vessel's hull symmetrically about the vessel's centreline, the hydrofoil surfaces being set at a dihedral angle and having means to vary the hydrodynamic lift produced by the hydrofoil surfaces independently.

14. A keel arrangement according to Claim 13, wherein the vessel is provided with a pair of bilge keels and a hydrofoil surface is arranged to extend outwardly and upwardly from the lower end region of each bilge keel.

15. A keel arrangment according to Claim 14, wherein a plurality of hydrofoil surfaces are mounted on each bilge keel.

16. A keel arrangement according to Claim 15, wherein at least one hydrofoil surface extends inboard from each bilge keel.

17. A keel arrangement according to any of Claims 14 to 16, wherein each bilge keel includes two hydrofoil surfaces set one behind the other.

18. A keel arrangement according to any of Claims 13 to 17, wherein the means to vary the hydrodynamic lift comprises means to rotate the hydrofoil surface about a spanwise axis to vary its momentary angle of incidence.

19. A keel arrangement according to claim 18, wherein each hydrofoil, surface is mounted for rotation about a spanwise axis and is provided with a control rod extending vertically into the vessel's hull, axial movement of the control rod causing rotation of the hydrofoil surface about its spanwise axis.

20. An apparatus according to any of Claims 2 to 12 or 14 to 19, wherein an indicator is provided to show the angular orientation of the hydrofoil surface.

21. An improved keel arrangement according to any preceding Claim, wherein a further hydrofoil surface is mounted on the vessel's centreline at its forward portion, said further hydrofoil surface being positioned at the lower end of a pylon extending downwardly from the vessel's hull and mounted thereto for rotation about a vertical axis.

22. An improved keel arrangement according to Claim 21, wherein a fin extends below the said further hydrofoil surface.

23. An improved keel according to Claim 14, wherein said bilge keels are rotatable about longitudinal axes passing through their upper regions, so as to provide an extended position wherein the hydrofoil surfaces are positioned away from the vessel's centreline and a retracted position wherein the hydrofoil surfaces are adjacent the vessel's centreline.

24. An improved keel arrangement according to Claim 23, wherein the hydrofoil surfaces are substantially horizontal in the retracted position.