GB2307457A

GB2307457A - Improvements in rigs for wind propelled vehicles

Info

Publication number: GB2307457A
Application number: GB9523807A
Authority: GB
Inventors: Duncan Guthrie
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-11-21
Filing date: 1995-11-21
Publication date: 1997-05-28
Anticipated expiration: 2015-11-21
Also published as: GB2307457B; GB9523807D0

Abstract

A rig 6 for a wind propelled vehicle, such as a sailing boat, comprises an aerofoil 8 and linkage means, for example arms 10 and 12, for connecting the aerofoil to the boat and transmitting force from the aerofoil 8 to the boat. The aerofoil 8 is held in an inclined position such that a net force acting upon the aerofoil has a lateral component (for propelling the boat) and an upward vertical component. The vertical component enables the hull of the boat to plane. Furthermore the linkage means holds the aerofoil 8 to the leeward side of the boat so that the upward force reduces or eliminates any rolling moment exerted on the boat by the aerofoil 8. There is also disclosed a method of achieving forward propulsion of a boat, by positioning an aerofoil 8 at an inclined elevated position relative to the boat, so that the net force acting on the aerofoil as a result of the interaction of the wind therewith acts along a line which passes through or near the effective centre of pressure of any balancing fin means 2 on the underside of the hull 1 so as to reduce or eliminate rolling movement of the hull 1 caused by the net wind force acting on the aerofoil 8.

Description

IMPROVEMENTS IN AND RELATING TO RIGS Field of the Invention This invention relates to a rig for a wind propelled vehicle, to a waterborne vehicle fitted with such a rig and to a method of achieving wind propulsion of a waterborne vehicle, such as a boat.

Background to the Invention An important factor which limits the performance of any boat is the hydrodynamic resistance of movement of the boat hull through the water. This resistance can be a particularly significant factor for a sailing boat, in which the propulsive force available to the boat can often be quite limited.

It has been known to equip the hulls of sailing boats with hydrofoils for lifting the hulls out of the water in order to reduce hydrodynamic drag. However, when the hull of such a boat is not raised, the hydrofoils increase the hydrodynamic drag experienced by the boat, and cannot therefore raise the hull if the wind provides an insufficient propulsive force to overcome the effects of that drag.

Furthermore, the action of the wind on the portion of the boat above the water can create a rolling moment. This is of a particular disadvantage in the case of a boat fitted with a hydrofoil, as the rolling moment will increase as the hull is raised from the water.

Consequently, boats fitted with hydrofoils are generally of a multi-hull design, or have hydrofoils which project a considerable distance from either side of a single hull.

Summary of the Invention According to the first aspect of the invention, there is provided a rig for a wind propelled vehicle, the rig comprising an aerofoil and linkage means for connecting the aerofoil to the vehicle and transmitting force from the aerofoil to the vehicle, said linkage means being operable to retain the aerofoil in at least one inclined position such that the net force acting upon the aerofoil as the result of the interaction of wind therewith has a lateral component for propelling the vehicle and an upward vertical component.

Such a rig is of particular advantage of use with a waterborne vessel, in which case the linkage means is arranged to connect the aerofoil to the hull of the vessel.

In this case, the linkage means is preferably operable to hold the aerofoil in such a position that in sufficiently strong winds, said upward vertical component lifts at least part of the hull out of the water, thereby reducing the hydrodynamic drag experienced by the hull, preferably to a sufficient extent to facilitate planing of the hull.

The upward force is generated by the aerofoil aerodynamically, and hence more efficiently, i.e. with a lower drag penalty, than hydrodynamic lift generated by a planing hull or hydrofoil. Accordingly, the overall lift to drag ratio of a sailing craft fitted with the rig can be high, giving rise to the possibility for high speed sailing in relatively low wind speeds, while requiring less physical exertion on the part of the person(s) sailing the craft, than is the case with known small sailing craft.

Additionally or alternatively, the linkage may be operable, when the direction of the wind is not along the elongate axis of the hull on which the rig is fitted, to hold the aerofoil in a position beyond the leeward side of the boat, so that said upward component at least reduces the rolling moment exerted on the boat by the aerofoil.

This feature makes the vessel relatively stable, enabling the rig to be used on a vessel having a single hull. It will be appreciated that this advantage will arise even if the upward force exerted by the aerofoil is not sufficient to raise the hull.

Preferably, the linkage means, in use, retains the aerofoil in an elevated position relative to the hull.

Preferably, the linkage means comprises two rigid members, each of which is pivotally attached to the aerofoil at a respective one of two spaced apart regions of the aerofoil, each rigid member also being pivotally connected to mounting means for mounting the rig on the hull of the vessel.

Preferably, the mounting means comprises a shaft to which each rigid member is pivotally attached at a respective one of two spaced apart regions of the shaft. The shaft could be mountable in a fixed angular position on the hull, but is preferably mountable on the hull for rotation about its own axis, and preferably about a pivot axis which is substantially perpendicular to the shaft axis.

Preferably, the rigid members and the shaft are co-planar, said plane preferably containing or intersecting said pivot axis.

In order to control the orientation of the aerofoil, the linkage means preferably includes one or more elongate flexible connectors, such as cables, which are selectively tensionable to alter the geometry of the linkage means. Those connectors are conveniently also connected to the shaft so that, in use, the cables tilt and rotate with the shaft.

The aerofoil may to advantage be of a lightweight construction, for example an inflatable sack or bag.

According to a second aspect of the invention, there is provided a waterborne vessel fitted with a rig according to the first aspect of the invention, and having fin means, such as a keel or centreboard, for counteracting the lateral wind forces exerted on the vessel.

Preferably, the geometry and orientation of the rig is adjustable so that the net force on the aerofoil resulting from the interaction of air therewith acts along a line which passes near or through the effective centre of pressure of the fin means.

Where the vessel has a single fin, the effective centre of pressure is that of the fin. On the other hand, where the vessel has multiple fins, for example a bilge keel, the effective centre of pressure is the net of the centres of pressure of the fins.

The invention also lies in a method of achieving forward propulsion of a waterborne vehicle, the method comprising the steps of positioning an aerofoil at an inclined elevated position relative to the vessel so that the net resultant of the forces acting on the aerofoil as a result of the interaction of the wind therewith acts along a line which passes through or near the effective centre of pressure of any balancing fin means on the underside of the hull so as to reduce or eliminate rolling movement of the hull caused by the net wind force acting on the aerofoil.

Brief Description of the Drawings An example of a rig in accordance with the invention will now be described with reference to the accompanying drawings which show a boat fitted with such a rig, and in which: Figure 1 is a side view of the boat; Figure 2 is a front of three quarters view of the boat, when the wind direction (relative to the boat) is the same as that from which the boat is being viewed; Figures 3 to 5 are front views of the boat respectively on a starboard tack, at mid tack and on a port tack; Figure 6 is a rear three quarters view, to an enlarged scale, of part of the boat, showing the connection of the rig to the boat hull; and Figures 7 to 9 are plan views of the boat when sailing at various different directions relative to the wind.

Detailed DescriDtion With reference to Figure 1, the boat has a hull 1 from the underside of which a centreboard 2 projects downwardly, and which is steered by means of a rudder 4 pivotally attached to the rear of the hull 1 in a conventional manner. The rig for the boat is shown generally at 6 and comprises an aerofoil 8 pivotally connected to two rigid members of the form of arms 10 and 12 which extend from the aerofoil 8 to a mounting means 14 mounted on the hull 1.

The outboard end of the arm 10 is provided with an aperture through which a shaft 20 extends with clearance. The ends of the shaft 20 are rotatably located within blind bores in two lugs 16 and 18 which project from the underside of the aerofoil 8. Thus, the arm 10 is connected to the aerofoil 8 so as to be pivotable about an axis defined by the shaft 20. The clearance between the aperture in the arm 10 and the shaft 20 also enables the arm 10 to pivot about an axis perpendicular to that of the shaft 20.

The arm 12 is connected to the underside of the aerofoil 8 at a spaced region from the connection of the arm 10 by a similar arrangement of a shaft 26 and lugs 22 and 24.

Thus the aerofoil 8 can pivot about an elongate axis which intersects the apertures in the tops of the arms 10 and 12. The aerofoil 8 carries a tail 62 which automatically trims the aerofoil 8 to ensure smooth airflow over the latter.

As can be seen from Figure 6, the end of the arm 12 opposite the aerofoil 8 is formed with a bracket 28 which is located on a T-piece 30 on the end of a shaft 32 by means of trunnions projecting from either side of the T-piece 30 into two bores in the bracket 28.

One such bore is visible at 34. The opposite end of the shaft 32 carries a T-piece 36 on which the arm 10 is mounted by means of a similar arrangement of trunnions extending into bores, for example 38, in a bracket 40 at the bottom of the arm 10.

The shaft 32 extends through two bearing blocks 42 and 44 at opposite ends of a bracket 46 which is attached to the top of a post 48. The post 48 is, in turn, rotatably mounted on the hull 1 so as to be rotatable about its axis.

Referring back to Figure 1, the points of connection of the arms 10 and 12 to the shaft 32 and the aerofoil 8 are co-planar, defining a plane WXYZ which is perpendicular to the axes about which the ends of the arms 10 and 12 can pivot. Thus, the arms 10 and 12, the aerofoil 8 and the shaft 32 define a co-planar quadrilateral linkage.

Since the shaft 32 can pivot about its own axis, the plane of that linkage can also pivot about the axis of the shaft 32. In addition, the assembly of the shaft 32 and bracket 46, and hence of the plane, can rotate about a vertical axis.

The geometry of the quadrilateral linkage can be adjusted by means of control wires 50 and 52 which extend between the shafts 20 and 26 and the shaft 32.

With reference to Figures 1 and 6, the wire 50 is attached to the shaft 20 and extends into a support tube 54 which is attached to a radial arm 56 which is fixed to the shaft 32, adjacent the bottom of the arm 12. Similarly, the wire 52 extends from the shaft 26 through a support tube 58 which is mounted on a radial arm 60 which is similar to the arm 56 and is situated adjacent the bottom of the arm 10. The arms 56 and 60 carry tensioning means (not shown) for controlling the tension in the wires 50 and 52.

Since the arms 56 and 60 are fixed to the shaft 32, the wires 50 and 52 rotate with the arms 10 and 12 about the axis of the shaft 32 and the axis of the post 48.

With the rig 6 in the state shown in Figure 1, the wire 52 is under tension, causing the linkage constituted by the aerofoil 8, the shaft 32 and the arms 10 and 12 to be skewed so that the aerofoil 8 is inclined, with its forward end 64 lowermost. When the boat is on the opposite tack, the tensioning is in the wire 50, which thus causes the aerofoil 8 to be inclined with the opposite end, which in that tack will also be the forward end, lowermost.

The operation of the rig will now be described in more detail.

With reference to Figure 2, the interaction of the wind with the aerofoil 8 generates two forces on the latter: a lift force, indicated by the arrow 66, which is substantially normal to the plane of the aerofoil 8, and a drag force in the direction of the wind. The drag will tend to push the aerofoil 8 in a leeward direction, hence urging the arms 10 and 12, and hence the shaft 32, to rotate in the direction indicated by the arrow 68. However, the lift force will tend to urge the arms 10 and 12 and the shaft 32 to rotate in the opposite direction.

Because the shaft 32 is free to pivot about its axis, the aerofoil 8 will move into a position, leeward of the hull, in which the moment about the shaft 32 attributable to the lift is balanced by that attributable to the drag.

Because the aerofoil 8 is inclined in the direction of movement of the boat 1, the lift force indicated by arrow 66 will have a vertically upward component and a forward horizontal component. The latter provides the propulsive force for the boat, whilst the former will tend to raise the hull 1 in the water so that, with sufficient wind, the hull 1 can plane.

The geometry of the arms 10 and 12 and their connection to the aerofoil 8 and the shaft 32 are such that the resultant of the lift and drag forces generated by the aerofoil 8 acts through the centre of pressure 70 of the keel 2. Consequently, the resultant aerodynamic force generated by the aerofoil 8 produces no heeling/rolling movement on the hull 1.

This is indicated by the line 72.

With reference to Figure 7, the interaction of the wind with the aerofoil 8 generates two forces on the latter: a lift force, indicated by the arrow 66, which is substantially normal to the plane of the aerofoil 8, and a drag force in the direction of the wind. The drag will tend to push the aerofoil 8 in a leeward direction, hence urging the arms 10 and 12 to rotate about the substantially vertical axis of the post 48 in the direction of arrow 80.

However, the lift force will tend to urge the arms 10 and 12 to rotate in the opposite direction.

Because the arms 10 and 12 are free to pivot about the axis of the post 48, the aerofoil will move into a position leeward of the hull, in which the moment about the post 48 attributable to the lift is balanced by that attributable to the drag.

The lift force exerted on the aerofoil 8 will tend to urge the latter into a horizontal position. This is resisted by the tension in the wire 52.

If the weight of the aerofoil 8 is not significant in relation to the lift, as would be the case in strong winds, then the aerofoil 8 would automatically move into a horizontal position, for example as shown in Figure 4, if the wire 52 is released. In this position, the lift generated by the aerofoil 8 has no forward or backward component.

Tensioning of the wire 50 and slackening of the wire 52 will move the aerofoil 8 into a position in which it is so inclined that the end 64 is uppermost. This position is illustrated in Figure 3 in which the boat is shown on a starboard tack. If the boat is then to tack through the wind, the hull is progressively turned so that the bow of the boat gradually turns into the wind, and as this happens, the wire 50 is slackened and the wire 52 tensioned. As this happens, the angle of inclination of the aerofoil 8 becomes progressively more shallow and the rig 6 rotates about the post 48 until the mid tack position shown in Figure 4 is reached. In this position, the aerofoil 8 is horizontal and the plane WXYZ substantially perpendicular to the axis of the hull 1.

Continuing movement of the hull 1 through the wind and tensioning of the wire 52 cause the rig 6 to continue to rotate about the shaft 48 and the end 64 of the aerofoil 8 to drop whilst the other end is raised until the rig reaches the position shown in Figure 5, in which the boat is on a port tack.

Various other positions of the rig for different wind directions are shown in Figures 7, 8 and 9. In all of these cases, the aerofoil 8 is so inclined that its forward end is lowermost so that the lift generated by the aerofoil 8 always has a forward horizontal component which propels the boat, whilst the vertical component raises the hull of the boat.

In Figure 7, the course of the boat is at 45O to the true wind direction, whilst in Figures 8 and 9, the course is respectively at 900 and 1350 to the true wind direction. It will be appreciated that the wind velocity relative to the aerofoil 8 is not the same as the true wind velocity in view of the forward motion of the boat. Figures 7, 8 and 9 therefore include vector diagrams which include a vector representing apparent wind velocity, i.e. the wind velocity relative to the boat, which is the vector sum of the true wind velocity and the boat velocity.

It will be appreciated from the foregoing that the invention provides an aerodynamic rig for a water borne vehicle which provides forward propulsion, a vertical lifting force to the vehicle without the use of hydrofoils, and causes no appreciable heeling moment to the craft. The advantages being high speed in relation to what might normally be expected for a given wind speed and ease of control.

Claims

1. A rig for a wind propelled vehicle the rig comprising an aerofoil and linkage means for connecting the aerofoil to the vehicle and transmitting force from the aerofoil to the vehicle, said linkage means being operable to retain the aerofoil in at least one inclined position such that the net force acting upon the aerofoil as the result of the interaction of wind therewith has a lateral component for propelling the vehicle and an upward vertical component.

2. A rig according to claim 1, in which the linkage means is arranged to connect the aerofoil to the hull of a waterborne vessel.

3. A rig according to claim 2, in which the linkage means is operable to hold the aerofoil in such a position that in sufficiently strong winds, said upward vertical component lifts at least part of the hull out of the water, thereby reducing the hydrodynamic drag experienced by the hull.

4. A rig according to claim 2 or claim 3, in which the linkage means is operable to hold the aerofoil in a position beyond the leeward side of the vessel, so that said upward component reduces the rolling moment exerted on the vessel bv the aerofoil.

5. A rig according to any of claims 2 to A, in which the linkage means. in use. retains the aerofoil in an elevated position relative to the hull.

6. A rig according to claim 5, in which the linkage means comprises two rigid members, each of which is pivotally attached to the aerofoil at a respective one of two spaced apart regions of the aerofoil, each rigid member also being pivotally connected to mounting means for mounting the rig on the hull of the vesse!.

7. A rig according to claim 6 in which the mounting means comprises a shaft to which each rigid member is pivotally attached at a respective one of two spaced apart regions of the shaft.

8. A rig according to claim 7, in which the shaft is not rotatable about its axis.

9. A rig according to claim 7 or claim S. in which the shaft, in use, is rotatable about a pivot axis which is substantially perpendicular to the shaft axis.

10. A rig according to claim i, in which the rigid members and the shaft are co-planar.

said plane containing or intersecting said pivot axis.

11. A rig according to any of the preceding claims, in which the linkage means includes one or more elongate flexible connectors, such as cables, which are selectiveiy tensionable to alter the geometry of the linkage means.

12. A rig according to claim 11 when appended to claim 9, in which the connectors are also connected to the shaft so that, in use, the connectors rotate about the pivot axis with the shaft.

13. A rig according to any of the preceding claims, in which the aerofoil is pivotable about its own axis, and carries a tail for trimming the aerofoil.

14. A waterborne vessel fitted with a rig according to any of the preceding claims, the vessel having fin means for counteracting the lateral wind forces exerted on the vessel by the rig.

15. A vessel according to claim 14, in which the geometry and orientation of the rig is such that the net force on the aerofoil resulting from the interaction of air therewith acts along a line which passes near or through the effective centre of pressure of the fin means.

16. A method of achieving forward prcpulsion of a waterborne vehicle, the method comprising the steps of positioning an aerofoi! at an inclined elevated position relative to the vessel so that the net resultant of the forces acting on the aerofoil as a result of the interaction of the wind therewith acts along a line which passes through or near the effective centre of pressure of any balancing fin means on the underside of the hull so as to reduce or eliminate rolling movement of the hull caused by the net wind force acting on the aerofoil.

17. A rig substantially as described herein with reference to, and as illustrated in, the accompanying drawings.

18. A boat substantially as described herein with reference to, and as illustrated in, the accompanying drawings.

19. A method substantially as described herein with reference to the accompanying drawings.