WO2003024781A1

WO2003024781A1 - Wind powered vehicle

Info

Publication number: WO2003024781A1
Application number: PCT/GB2002/003683
Authority: WO
Inventors: John Godfrey Morley
Original assignee: John Godfrey Morley
Priority date: 2001-08-14
Filing date: 2002-08-08
Publication date: 2003-03-27

Abstract

A wind powered vehicle, such as a sailing boat, comprises a vehicle body (36), a mast (10) mounted on said body, a sail (32) secured to a spar (12), means (14,16,18 and 20) attaching the spar to the mast to allow the spar to rotate to an equilibrium position in a plane containing the mast, a boom (30) rotatable about the spar (12) and means for controlling the rotation of the boom about the spar. The means attaching the spar to the mast may include upper and lower link members (14) and (16), the lower link member (16) being longer than the upper link member (14).

Description

WIND POWERED VEHICLE

This invention relates to a wind powered vehicle, and in particular to a such a vehicle with a kite sail, i.e. a sail which gives lift in addition to propulsion and, in the context of a boat, largely eliminates any heeling effect.

When applied to a boat such as a catamaran, the lift from a kite sail reduces the effective displacement of the hulls of the boat thus reducing their hydrodynamic resistance and permitting higher boat speeds. Maximum speeds are obtained when the lift from the sail almost equals the weight of the boat. Under these conditions sudden changes in wind speed and/or direction can produce sudden increases in lift, and similar effects can be produced by a sudden change in the attitude of the boat due, for example, to wave action. Unless compensated for these effects can cause the boat to be lifted out of the water, a situation that is undesirable and dangerous.

It is an object of the present invention to obviate or mitigate this problem, in particular by providing means to compensate for those effects which can cause the boat to lift out of the water.

A kite sail driven boat is capable of very high speeds when reaching with the wind on the beam, but on other points of sailing boat speeds are less and a larger keel area may be required for adequate control. Embodiments of the present invention allow extra keel area to be added when required.

The present invention also allows the sail to be used in a conventional way when this is more appropriate. The present invention is a wind powered vehicle comprising a vehicle body, a mast mounted on said body, a sail secured to a spar, means attaching the spar to the mast to allow the spar to rotate to an equilibrium position in a plane containing the mast, a boom rotatable about the spar and means for controlling the rotation of the boom about the spar.

The vehicle may be a boat and is preferably a catamaran.

Preferably, the links are attached to a top portion of the mast which is rotatable about its own axis relative to the vehicle body.

At least one of the link members may be connected to the mast by a pin joint.

Preferably, at least one of the link members has a connection to the mast which can slide on the mast.

Preferably at least one of the link members is connected to the spar by link joints.

The geometry of the spar and link members may be such that the resultant force generated by the sail passes close to the centerline of the vehicle body.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a schematic view of a sail rig according to the present invention; Fig .2 is a view of the rig of Fig. 1 with the sail in a different position relative to the mast; Fig. 3 is another view of the rig of Fig. 1 with the sail raised further and showing means by which a hydrovane can be immersed; Fig. 4 illustrates an alternative sail configuration; Fig. 5 illustrates a portion of Fig. 3 in more detail;

Fig. 6 illustrates a sail release mechanism; Figs 7a and 7b illustrate an alternative sail release mechanism; Fig. 8 illustrates a means for rotating the sail boom about the sail spar; and Figs. 9a and 9b illustrate further sail release mechanisms.

Referring now to Fig, 1, a sail rig according to the present invention includes an upright mastlO, and a spar 12 attached to the mast by two vertically spaced link members, an upper one 14 a lower one 16. In this embodiment the link members 14 and 16 are connected to the mast 10 by respective pin joints 18 and 20. The spar 14 is attached to the link members 14 and 16 by respective pin joints 26 and 28, and a boom 30 is pivotally mounted at the bottom of the spar 12. A kite sail 32 is secured at its luff to the spar 12 and at its foot to the boom 30. The boom 30 can pivot about the spar 12, and means to control this pivotal movement will be described in more detail later.

An alternative sail arrangement is shown in Fig. 4. Here the sail has a large area forward of the spar 12 and this acts as an aerodynamic balance to reduce the magnitude of the control loads. The sail spar 12 is held by and can rotate within bearings attached to the pin j oints 26 and 28. A forward boom 37 and a rear boom 38 are attached to the sail spar near the joint 28. These booms may be similar to those fitted to windsurfer sails, i.e. external to the sail and arranged one on each side of it.. The sail may be held in the shape illustrated by the use of battens.

The mast 10 is mounted in the body 36 of a vehicle, in this embodiment a sailing boat, specifically a catamaran, the upper section of the mast which incorporates the joints 18 and 20 being rotatable relative to the body 36.

To understand the operation of the sailing rig illustrated, we first consider the joints 18, 20, 26 and 28 to be fixed, and the upper section of the mast fixed against rotation, and the boom 30 still free to rotate on the spar 12. The rig now behaves as a conventional rig but with the sail 32 spaced some distance from the mast 10. If now we allow rotation of the upper section of the mast to occur, rotation of the boom 30 about the spar 12 causes the wind to produce on the sail a force perpendicular to the direction of the wind in addition to a drag force on the sail parallel to the wind. These forces cause the sail to rotate about the mast via the bearing 37, incorporating the pin joints 18 and 20, to an equilibrium position in azimuth when the aerodynamic forces tending to rotate the sail about the mast bearing in one direction are balanced by the forces tending to rotate it in the other. The overall effect is to produce a force acting on the sail in a direction away from the mast. If we now consider the pin joints 18, 6, 20 and 28 to be free, the combined forces acting on the sail cause it and the sail spar 12 to move away from the mast in an upwards direction, i.e. the spar rotates in a plane containing the mast. Further rotation of the boom 30 about the spar 12 increases the aerodynamic force on the sail producing a further rotation of the sail about the mast 10 and further upwards movement of the sail. These changes in geometry are in balance because of the inherent negative feed back characteristics of the system. This helps to overcome any problems due to instability. When the sail moves upwards to the configuration shown in Fig. 2, the aerodynamic force generated has a significant upwards component as well as a horizontal component perpendicular to the wind and a drag force parallel to the wind.

The movement of the sail upwards can be limited to some desirable configuration, e.g. the condition at which the heeling effect is reduced to negligible values.

Under these conditions, the large upward force developed by the sail tends to lift the boat out of the water thus reducing the hydrodynamic drag of the hull allowing high boat speeds to be achieved..

The magnitude of the aerodynamic force developed by the sail is governed by the velocity of the wind blowing over the sail, the apparent wind. The apparent wind is the vector sum of the boat speed and the true wind speed, and the aerodynamic force developed by the sail is proportional to the square of the apparent wind speed. Maximum boat speeds are developed when the direction of the true wind is approximately at right angles to the direction of motion of the boat and this particular condition will now be considered. Since the boat would be expected to travel at upwards of twice the true wind speed it follows that the aerodynamic force on the sail developed by the apparent wind at these boat speeds will be several times greater than that developed by the true wind alone. Although the vertical component of the sail force reduces hull drag and hence allows high boat speeds to be developed, it is necessary to prevent it becoming large enough to lift the boat out of the water.

This can be prevented by arranging for the sail to move upwards to a more nearly horizontal position when the vertical component of the sail force becomes inconveniently large. At first sight this would seem merely to increase the vertical component of the sail force, but in fact the upward movement of the sail reduces the forward driving force which generates the speed of the boat and hence the magnitude of the apparent wind. Hence, if the sail is permitted to move upwards, the boat speed and the apparent wind speed fall thus reducing the magnitude of the aerodynamic force tending to lift the boat out of the water, and this is despite the fact that the vertical component of the of the aerodynamic force generated by the sail increases as the sail becomes more horizontal.

If the sail is completely horizontal, the forward driving force will be zero and in these circumstances the boat would not move in the water and the sail would be subjected only to the true wind. By arranging for the upward movement of the sail to occur before the vertical component of the aerodynamic force generated by the sail exceeds the weight of the boat, lift offcan be prevented. The upward movement of the sail can also be used to insert a hydrovane into the water, as indicated in Fig.3 , so as to produce a downward and also rearward force to assist in preventing the boat leaving the water. When arranged in this manner the hydrovane does not contribute to the hydrodynamic drag ofthe boat under normal sailing conditions. Fig. 3 gives a schematic view of a possible arrangement. The hydrovane 40 is carried on an arm 41 which is pivoted at its end by a bearing 42. A line 49 is attached to the arm 41 and to a device 43, which will be described in more detail later, on the upper rotatable part ofthe mast 10. The device 43 is in turn attached to a short arm 44 projecting from the end ofthe linkmember 14. The length ofthe line is such that as the sail approaches a horizontal position the rotation ofthe arm 44 about the pin joint 18 allows the hydrovane to be inserted into the water. When the sail spar 12 returns to its normal operating condition the hydrovane is pulled out ofthe water. Clearly the same mechanism can be used to insert a larger keel at the same time.

Since the sail and the top section ofthe mast 10 can rotate with respect to the body of the boat, it is necessary for the link 43 to be capable of accommodating this rotation. One means of achieving this is shown schematically in Fig.5. An inner collar 45 can move up and down the rotatable part ofthe mast 10 but is constrained to rotate with it. The collar 45 is attached to the arm 44 by a strut and link pins. An outer collar 46 can rotate about the mast 10 relative to the collar 45 but is constrained to follow the upward and downward movements ofthe collar 45. The outer collar carries a strut 47 which passes through a guide 48 which is in turn attached to the fixed lower section ofthe mast or to the body ofthe boat. The upper end ofthe line 49 is attached to the lower end ofthe strut 47. There are various ways by which the sail could be released to take up a more nearly horizontal position. If the sail is held down manually by a sheet held by the helmsman then the sheet may simply be released. Alternatively, automatic means may be provided, for example a simple piston arrangement as shown in Fig. 6, and this could be pneumatic or hydraulic. As seen in Fig. 6, the piston 50 is held at one end ofthe cylinder 52 by a light spring 54. The piston carries one or more pressure relief valves 56. As the load on the piston rod reaches the design limit, the pressure developed in the cylinder 52 allows the fluid in the cylinder to flow through the open pressure relief valves. The piston 50 then travels to the other end ofthe cylinder and suitable linkages then allow the sail to swing upwards. When the loads are reduced the light spring 54 returns the piston to the other end ofthe cylinder, a nonreturn valve 58 in the piston allowing the fluid in the cylinder to flow past the piston as this occurs.

The action ofthe system is as follows. When the crucial design load is reached, the pressure relief valve 56 opens and the piston 50 starts to move thus releasing the sail and allowing it to move upwards. This action takes place at a constant load on the sail set by the pressure relief valve. As the sail moves upwards, the instantaneous vertical lift component will increase, since the boat will not stop suddenly, so that the vertical load on the sail will increase. However the load transmitted to the boat via the compressed fluid in the cylinder will remain constant, being set by the pressure relief valve. The excess aerodynamic force accelerates the rotation ofthe mass ofthe sail as it moves to a more horizontal position. As this is occurring, the forward driving component ofthe sail is falling so that the boat speed, the apparent wind speed and the aerodynamic force on the sail are all falling rapidly. At the same time the hydrovane may be entering the water slowing the boat further and, more importantly, producing a downward force on the boat.

When the sail is released by a trigger mechanism, the instantaneous lift provided by the sail will be almost zero. This is important in that a very rapid response to incipient lift off is generated in this way. The sail will generate lift only when it reaches its new stop position. One method by which this may be achieved is illustrated in Fig. 7. A piston and cylinder similar to that shown in Fig. 6 is provided but the piston is somewhat shorter and does not contain the light return spring 54. In Fig.7a the piston rod 60 is connected to a cam 62 by a link 61 and rotatable joints 63 and 64. The cam 62 can rotate about a pin 63. A further cam 65 locates around cam 62 and at its further end is attached to the sail spar 12, Under normal sailing conditions the aerodynamic load on the spar 12 is therefore transmitted to the cam 65 and thence to the cam 62 and the piston 50. The working fluid used in the cylinder 52 is such that no appreciable movement ofthe piston takes place until the pressure ofthe fluid reaches the release pressure for the valve 56. When this, and the corresponding load on the spar 12 is reached, the piston moves releasing the cam 65 as shown in Fig. 7b. The cam 65 is now free to travel against the force ofthe light return spring 66 so that the sail can move up to an almost horizontal position. When the force on the sail is reduced so that it returns to its normal operating position, the light return spring 66 returns the cam 65 and the piston 50 to their original positions. In a further modified embodiment lift off is prevented by arranging for the upward movement ofthe sail to be resisted by a spring or other resilient restraint located between the mast and the boom. In this modified embodiment the upward movement of the sail, and hence the ratio ofthe lifting to drive component forces, will change as the velocity of the apparent wind increases. The sail will assume a more horizontal position the greater the velocity ofthe apparent wind. It will of course be necessary to arrange for the spring constant to be such that the angle made by the sail to the horizontal to be insensitive to changes in the vertical lift developed by the sail up to some critical value near to lift off conditions. Further small increases in vertical lift would then produce large changes in sail angle thus preventing lift off as previously described.

It is necessary to apply a force to the sail spar 12 , or to one of its link members 14 or

16 in order to hold it at some particular angle to the horizontal when under aerodynamic load. As discussed above, it is advantageous for this force to change its magnitude in a non-linear way as the sail becomes more nearly horizontal. This can be achieved by spring loaded systems and one possible embodiment is shown in Fig 9a in which two arms 101 and 102 are joined together and pivoted at 100. A line 109 connects the end ofthe arm 101 to the spar 12, or a conjoined link, via a pulley 107 so that as the sail spar moves upwards or downwards the angle θ changes and the arms 101 and 102 rotate about 100. A spring 108, generating a force R, is attached to the end ofthe arm 1 2 to restrain the upward movement ofthe sail which generates a force S on the line 1 9 attached to the arm 101. The relationship between R and S as the angle θ changes is dependent on the relative lengths ofthe arms 101 and 102 as well as on φ, the angle between them. It is also dependent on the absolute value of θ. In a further embodiment, illustrated in Fig 9b, a link 103 is attached by a pin joint 106 to the arm 102 so that it engages with the pivot 100 when the arm 102 becomes vertical. Further rotation of the arms 101 and 102 in a clockwise direction about the pivot 100 produces a new relationship between R and S. If the distance along the link 103 from the pin joint 106 to the point of attachment ofthe spring is nearly the same length as the arm 102, further rotation ofthe arms 101 and 102 produces little further extension ofthe spring and if the link 103 is arranged to locate around the pivot 100, as shown in Fig. 9b, the spring load R becomes supported by the pivot 100 so that the load on S is reduced virtually to zero.

If the link 103 extends beyond the pivot 100, as indicated in Fig.9b, then yet a further relationship between R and S will be developed. Further adjustments can also be made through variations in the geometry ofthe from ofthe attachment ofthe line 109 to the sail spar.

Control ofthe rotation ofthe sail about the spar 12 can be achieved by various means. A possible arrangement is illustrated in Fig.8 which gives a perspective view ofthe structure in the vicinity ofthe joint 28 in Fig.3. The sail spar 12 is carried by a bearing 70 near the pin joint 28 and by a similar bearing at the pin joint 26. The spar 12 carries two struts 71 and 72 between the two sections ofthe bearing 70. The struts 71 and 72 are angled downwards and backwards from the spar 12. These struts carry the twin forward and rearward booms 37a and 37b and 38a and 38b which are located on each side ofthe sail. The geometry is such that the forward booms 37a and 37b do not foul the joint 28 as the sail spar 12 rotates through plus and minus 90°. Control ofthe sail is achieved through lines attached to the extremities ofthe struts 71 and 72. One such line is indicated in Fig.8. The lines pass through fairleads located at the pin joints 28 and 20, and from there to the foot of the mast and the helmsman. Stiffening wires 73, 74, 75 and 76 may be included to inhibit flexing ofthe sail spar 12.

Supporting wires such as stays and shrouds may be fixed as desired to the mast below the joint 20 or it lowest point if it can move up and down, and of course the mast should not be able to rotate where the supporting wires are attached.

Alternatively, the mast can be arranged to be self supporting and to rotate about a bearing near its foot.

In operation, the prirtiary loads act along the link members 14 and 16, and the aerodynamic centre ofthe sail can be arranged to be near the joint 28 so that flexing loads on the spar 12 are minimised. Any out of balance loads can be accommodated by stiffening wires along the spar 12 and by the upper section ofthe mast, between the joints 18 and 20, acting as a torsion tube.

When not in operation, the sail can be deployed in a substantially vertical position which is convenient for mooring. Also, the rig can be operated as a conventional sail, though spaced from the mast, if conditions make this a more appropriate mode of operation.

The vehicle could be other than a boat, for example a land yacht.

Claims

1. A wind powered vehicle comprising a vehicle body, a mast mounted on said body, a sail secured to a spar, means attaching the spar to the mast to allow the spar to rotate to an equilibrium position in a plane containing the mast, a boom rotatable about the spar and means for controlling the rotation ofthe boom about the spar.

2. A vehicle as claimed in claiml, in which the means attaching the spar to the mast comprises upper and lower link members, the lower link member being longer than the upper link member

3. A vehicle as claimed in claim 1 or claim 2, the vehicle being a boat.

4. A vehicle as claimed in claim 3, in which the boat is a catamaran.

5. A vehicle as claimed in any of claims 2 to 4, in which the links are attached to a top portion ofthe mast which is rotatable about its own axis relative to the vehicle body.

6. A vehicle as claimed in any of claims 2 to 5, in which at least one ofthe link members is connected to the mast by a pin joint.

7. A vehicle as claimed in any of claims 2 to 6, in which at least one ofthe link members has a connection to the mast which can slide on the mast.

8. A vehicle as claimed in any of claims 2 to 7, in which at least one ofthe link members is connected to the spar by link joints.

9. A vehicle as claimed in any of claims 2 to 7, in which the geometry ofthe spar and link members is such that the resultant force generated by the sail passes close to the centerline ofthe vehicle body.

10 A vehicle as claimed in any preceding claim, in which the equilibrium is determined by the rotation ofthe boom about the spar.

11. A vehicle as claimed in claim 10, including means responsive to the force exerted by the sail for allowing the spar to move upwardly from its equilibrium position.

12. A vehicle as claimed in claim 11, in which the means responsive to the force exerted by the sail includes a resilient restraint located between the mast and the boom.

13. A vehicle as claimed in claim 11 , in which the means responsive to force exerted by the sail includes a cylinder having apiston therein, and apressure responsive valve connecting one end ofthe cylinder to the other.

14. A vehicle as claimed in claim 13, in which the piston is biased towards said one end ofthe cylinder, and the valve opens to allow fluid to pass from the other end ofthe cylinder to said one end.

15. A vehicle as claimed in claim 14, in which the piston includes a second pressure responsive valve which opens to allpw fluid to pass from said one end to said other end ofthe cylinder.

16. A vehicle as claimed in any of claims 11 to 15, in which a hydrovane is connected with the spar and the vehicle body whereby when said means responds to the excessive sail force the movement ofthe spar causes the hydrovane to be inserted into the water to cause a downward and rearward force on the vehicle.

17. A vehicle substantially as hereinbefore described with reference to and as shown in the accompanying drawings.