GB2226281A

GB2226281A - Hydrofoil keel

Info

Publication number: GB2226281A
Application number: GB8829293A
Authority: GB
Inventors: Peter Bernard Jeffreys
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-12-15
Filing date: 1988-12-15
Publication date: 1990-06-27
Anticipated expiration: 2008-12-15
Also published as: EP0373913B1; DE68908860T2; DE68908860D1; GB8829293D0; GB2226281B; EP0373913A1

Description

1 "IMPROVED KEEL" 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 independantly orientable so that their combined effect is to 2 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 centreline, 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 t.o 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, 3 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 the 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 hyrofoil 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.

4 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.

Two embodiments of the invention will now be described with reference to the accompanying drawings, in which, Figure I 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, and Figure 7 is a schematic view of a control system for one of the hydrofoil surfaces shown in Figures 5 and 6.

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 plyons 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 1OL, 1OW, 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 1OW, 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, 6 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, 1OW 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 1OW to an inverted position, its "lift" force F is arranged to act downwardly and thus the combined effect of the two hydrofoil 7 surfaces 10L and 1OW 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 hydroifoil surface IOL is directed upwardly and inclined slightly to windward of the vertical, and the windward hydrofoil IOW 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 1OW 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, 1OW, 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.

8 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 cente 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.

1 9 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 surfaces. In such cases the hydrofoil will be "feathered" by releasing the locking screw 31 and allowing the hydrofoil surfaces to adopt a zero incidence position.

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.

11

Claims

An improved keel arrangement for a sailing vessel, comprising at least 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 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 12 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 Claims 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.
is. A keel arrangement 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.

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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.

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