GB2080227A - Self-steering gear for yachts - Google Patents

Abstract

A self-steering gear for a yacht, comprising a servo-rudder blade 17 attached to the lower end of a servo-rudder shaft contained within a bearing tube 11, which tube forms part of a carrier 10 adapted for pivotal mounting on the stern of a yacht about a generally vertical axis. The servo rudder shaft extends rearwardly from and downwardly at an acute angle to the pivotal axis of the carrier, and there is provided a wind vane assembly including a vane element 24 mounted for rotation about a generally vertical axis either coincident with or substantially parallel to the pivotal axis of the carrier. A coupling 18, 21, 22 having a non-linear action is arranged to interconnect the servo-rudder shaft and the shaft of the wind vane, whereby the wind vane may turn the servo-rudder shaft, dependent upon the apparent wind direction. The carrier 10 is adapted for transfer of its movement about its vertical axis to the main rudder of the yacht, the carrier itself being turned by the action of the servo-rudder blade. <IMAGE>

Description

SPECIFICATION Self-steering gear for yachts The present invention relates to a self-steering gearforyachts, and in particular concerns a windvane self-steering gear.

A wind-vane self-steering gear for a yacht operates to provide an automatic steering system to keep the yacht at a constant angle to the apparent wind, when underway. Such a self-steering gear includes a wind-vane which can be set so that it is aligned with the apparent wind for any particular course setting, and mounted so that when the yacht goes off course the tendency of the vane to remain aligned with the wind exerts a force on a servo-rudder blade mounted below the water-line, urging the servorudder blade out of alignment with the water flow.

The servo-rudder blade is suitably connected either to the main rudder of the yacht orto an auxiliary rudder so that the restoring couple on the servorudder blade created by the water flow turns the main rudder or the auxiliary rudder to alter the heading of the yacht. As the yacht returns to its original heading, the wind vane once more becomes aligned with the apparent wind (presuming the wind direction has not meanwhile changed) removing the force applied to the servo-blade.

There are two main kinds of known servo-rudder blade mounting arrangements: one ofthese mounts the blade to pivot about a vertical axis (considering the yacht in a 'normal' attitude) and the other mounts the blade to pivot about a horizontal axis or an axis typically not more than 20 to the horizontal (pendulum type). The former arrangement has the advantage that the servo-rudder blade is essentially always immersed to the same depth, which improves its efficiency, and is less likely than a pendulum type to suffer damage due to the partially immersed blade crashing back into the water when the yacht is pitching.However, in the known arrangements of the former type, there is the disadvantage that the force which can be exerted on the main rudder or the auxiliary rudder is relatively small unless a very large servo-rudder blade is employed, and moreover complex and massive arms are usually required to support the servo-blade sufficiently aft of the vertical axis to provide a reasonably large torque and far enough aft of the main yacht rudder in order to avoid interference therewith.

It is a general aim of this invention to provide a self-steering gear for a yacht, which at least mitigates to some extent the disadvantages of the known type of self-steering gear having a vertical axis servo-rudder blade whilst still retaining reliabie operation.

Accordingly, this invention provides a selfsteering gear for a yacht, comprising a servo-rudder blade attached to the lower end of a servo-rudder shaft mounted for rotation about its axis on a carrier, means for mounting the carrierto the stern of a yacht such that when so mounted and with the yacht in a normal attitude the carrier may turn about a second axis extending generally vertically and the servo-rudder shaft axis lies generally in a common plane with said second axis, the servo-rudder shaft extending rearwardly from and downwardly at an acute angle to said second axis, a wind vane sensor shaft mounted for rotation about a third axis substantially parallel to or co-incident with said second axis, coupling means drivingly interconnecting the servo-rudder shaft and the sensor shaft whereby turning movement of one shaft is imparted to the other shaft, a wind vane adapted to turn the sensor shaft in dependence upon the apparent wind direction, and rudder drive means adapted to allow transfer of turning movement of the carrier about said second axis to the main rudder of the yacht when the gear is mounted on the yacht.

When the self-steering gear of this invention is being used, once a course has been set and the wind-vane aligned with the apparent wind, the wind-vane will move relative to the yacht should the yacht deviate from its original heading, and the sensor shaft is turned thereby. This causes the servorudder shaft to be turned, moving the servo-rudder blade out of alignment with the water flow, resulting in a force being exerted on the servo-rudder blade.

This force applies a couple to the carrier, turning the carrier until the servo-rudder blade is substantially aligned with the water flow, and the carrier movement is transferred to the main rudder of the yacht, to alter the heading. The senses of operation of the coupling means between the servo-rudder shaft and the sensor shaft, and of the rudder drive means should be arranged such that equilibrium can be reached when the yacht is back on its original heading -that is to say, the correction applied to the main rudder when the wind-vane senses a deviation from the original heading is such that the yacht is turned back to its original heading.

It will be appreciated that the self-steering gear of this invention has the servo-rudder blade mounted on a shaft which (in the normal disposition of the yacht fitted with the gear) lies at an acute angle to the vertical, the servo-rudder blade itself being disposed considerably rearwardly of the vertical axis of movement of the servo-rudder shaft carrier. The means supporting the carrier can thus be constituted by quite short arms (as compared with known vertical-axis servo-system self-steering gears) and yet the servo-rudder blade can be sufficiently aft of the main rudder to avoid interference therewith.

Moreover, the relative disposition of the inclined servo-rudder shaft axis, the generally vertical second axis and the third axis of the wind-vane sensor shaft allow a simple and compact coupling means to be employed between the sensor shaft and the servorudder shaft. In addition, since movement of the servo-rudder blade causes a turning moment to be applied to the carrier about the second axis and the servo-rudder blade is spaced considerably from the second axis, a relatively small servo-rudder blade can nevertheless impart a high force to the main rudder of the yacht.

The wind-vane, which senses the apparent wind direction, can take a variety of forms. For example, the vane can be simple weather-cock device, having a generally-horizontally extending arm provided with a weather-cock vane at one end thereof, the arm being directly attached to the sensor shaft to cause turning movement thereof upon a change in the apparent wind direction. If required, the arm may extend beyond its attachement to the sensor shaft to carry a counter-weight, whereby a balanced weather-cock device is provided. An alternative is for the wind-vane to be a so-called 'flip-flop' device, having a vane carried on a shaft mounted for rotation about a generally horizontal axis, the vane upstanding from the shaft and a relatively heavy weight being attached to a downwardly extending arm also attached to the shaft.Then, on the vane coming out of alignment with the wind, the vane is urged over sideways to such an extent that the force thereon is balanced by the couple applied to the shaft by the weight. For such an arrangement, a suitable mechanism must be provided to interconnect the vane shaft and the servo-rudder shaft, such as a flexible drive shaft, a toothed gear train a line and pulley, a pin and slot coupling and so on. Yet another possibility is to use a modified form of flip-flop vane, where the axis of rotation of the vane shaft can be adjusted to lie horizontally or at some angle to the horizontal, to suit the particular conditions of wind strength and direction, yacht movement and loading, and soon.

Whatever the form of wind-vane, the performance thereof can be enhanced by appropriate configuration of the vane itself. For instance, the known single plane wind vane element could be replaced by two or more considerably smaller vanes mounted sideby-side, each vane element being either a flat plate or of symmetric or assymmetric aerofoil section.

Such an arrangement can increase the lift force generated by the vane, due to the slot effect of the closely-spaced parallel vane elements and for appropriate configurations also due to the Venturi effect therebetween. In addition, a much stronger but lighter vane may be constructed using a box configuration.

To permit the setting of a desired heading for a given apparent wind direction, there must be provided means allowing relative adjustment between the servo-rudder shaft and the wind-vane position.

For example, in the case of a weather-cock device, the arm thereof can adjustably be mounted direct on the sensor shaft. Then, to set up self-steering action when a particular course is being followed and the main rudder already at the appropriate angle, all that is necessary is for the wind-vane to be aligned with the apparent wind whereafterthe vane arm is locked to the sensor shaft. Then the main rudder may be freed from manual control, subsequent adjustment thereof being made by the self-steering gear upon a change in apparent wind direction being sensed.

for a flip-flop vane device the mechanism interconnecting the vane shaft and the sensor shaft could be made adjustable. Another possibility is to provide adjustment means between the sensor shaft and the coupling means interconnecting the sensor shaft and the servo-rudder shaft.

The coupling means between the servo-rudder shaft and the sensor shaft may be in the form of mating gears adapted to accommodate the lack of parallelism between the two shafts. It is however advantageous for the coupling means to have a non-linear action, for this can assist the stable opera tion of the self-steering gear. Such an action can conveniently be obtained with the coupling means in the form of a pair of crank arms, one mounted on each shaft respectively and one crank arm having a peg which is received in a slot in the other crank arm.

Such a mechanism is moreover cheap to manufacture and easy to service.

The carrier advantageously has a bearing tube in which is supported the servo-rudder shaft, the tube extending for substantially the whole length of the shaft from the servo-rudder blade to the coupling means. Preferably, the carrier also comprises a further tube about the axis of which the carrier is rotatably mounted on the yacht, the bearing and further tubes being fastened together at an appropriate spacing and with an appropriate acute angle therebetween.The acute angle is preferably not more than 45 , and an appropriate range of angles may be from 15"to 35 . Most preferably, the angle is substantially 259 for this mounts the servo-rudder blade sufficiently rearwardly of the carrier axis to allow the generation of sufficient torque when the servo-rudder blade is turned out of line with the water flow, and also places the servo-rudder blade conveniently aft of the yacht main rudder.

The mounting meansforthecarriershould be suitable for mounting the carrier on the stern of a yacht, with the second axis (i.e. the axis of movement of the carrier) generally vertical. For instance, the mounting means may comprise a pair of arms each suitable for attachment to the yacht stern at one end and supporting a spindle at the other end thereof, which spindle extends vertically and has the further tube of the carrierjournalled thereon.

Preferably, the sensor shaft is supported by and mounted in a tube forming a part of the carrier, to lie co-axial with the second axis. Conveniently, the end portion of the servo-rudder blade extends forward of the second axis, the coupling means then being provided at the free end of the other end portion. In this way, the coupling means as well as the wind-vane may be accessible with relative ease from the stern of the yacht- which may not be the case with a self-steering servo-system having a vertical shaft.

Another possibiiity is for the sensor shaft to be mounted directly on the yacht itself, the servorudder shaft terminating at its upper end adjacent the sensor shaft for connection thereto by the coupling means.

The rudder drive means preferably comprises cords attached to a cross-tree or quadrant on the carrier and connected to the tiller (for a tillercontrolled yacth) such that turning movement of the carrier causes movement of the tiller in the required sense. In the preferred form of carrier, a cross-tree is provided which has two arms extending transversely of the carrier and attached to the bearing tube in which the servo-rudder shaft is mounted, at a position along the length thereof where the axis thereof intersects the second axis. In this way, apparent changes in length of the cords on turning movement of the carrier can be kept to a minimum.

Advantageously, each cord may extend forwardly from an end ofthe cross-tree, pass round a pulley on the tiller, and then be made fast at a suitable point on a side of the yacht opposed to the end of the crosstree to which that cord is attached. Another possibility is to have a single cord which passes around four pulleys mounted on the yacht so as to define a loop, the tiller being connected to one transverse run of the cord and a quadrant on the carrier being connected to another, opposed transverse run. More complex mechanical arrangements could be devised, but these are not preferred in view of the arduous service conditions on board a yacht and the need for high reliability coupled with easy servicing in the event of a component failure.

The preferred forms of wind-vane device described above may be used if desired with known forms of self-steering gear.

Thus, according to another aspect ofthis invention, there is provided a wind-vane device for a selfsteering gear, comprising a strut carrying at one end thereof two or more spaced wind-vane elements each disposed generally parallel to the or each other element and parallel to the length of the strut, each element being of essentially the same shape and area as the or each other element, the strut carrying at the other end thereof a counter-weight for the vane elements, and a mounting being provided part-way between the ends of the strut to allow connection of the strut to a sensor shaft extending in a direction substantially normal to the length of the strut and parallel to the general planes of the vane elements.

The vane elements and the counter-weight may be moveable along the length of the strut, to allow adjustment of the force applied to the vane sensor shaft. Moreover, each vane element may be of simple laminarform, or may be of symmetric or assymetric aerofoil section, to allow an increase in the lift force generated by the overall vane.

Though the vane elements are mounted generally parallel, the two elements (in the case of a twoelement vane) or the outer two elements (in the case of a multi-element vane) may be mounted at a small angle to one another (for example, less than 10 ) with the parallel edges extending generally parallel to the sensor shaft (when mounted thereon) and with the widest-spaced parallel edges furthest from the sensor shaft. This wedge-shaped configuration can impart dynamic stability to the vane when in use, and moreover the spaced vane elements gives greater sensitivity to apparent wind direction due to the slot effect of the spaced vane elements. Also, for aerofoil section elements, the consequent Venturi effect can increased the lift force, generating a greaterturning moment.

By way of example only, certain specific embodiments of self-steering gear for a yacht constructed in accordance with this invention will now be described in detail, reference being made to the accompanying drawing, in which; Figure lisa perspective view of the stern part of a yacht to which an embodiment of self-steering gear constructed in accordance with this invention has been fitted; Figure 1 a is a detail view of part of a self-steering gearofthis invention; Figure 2 is a schematic representation of a modified form of self-steering gear of this invention; Figure 3 is a schematic representation of another modified form of self-steering gear of this invention;; Figure 4 is a schematic representation of an alternative arrangement for transmitting the output from the self-steering gear of this invention to the tiller arm of a yacht to which this self-steering gear is fitted; and Figures 5a and 5b illustrate details of two forms of wind sensor for use in self-steering gear constructed in accordance with this invention.

Referring to Figures 1 and la, the self-steering gear comprises a carrier 10 of co-planartubular construction which consists of a longitudinal servorudder shaft support tube 11, a bearing tube 12 arranged at an angle of approximately 25" to the servo-rudder shaft support tube and spaced therefrom by arms 13, and a wind sensor shaft support tube 14 attached to the longitudinal support tube 11, so as to extend co-axially with the bearing tube 12.

Brackets 15 support a shaft (not shown) generally vertically, on which shaft is journalled bearing tube 12 for rotation, whereby the carrier 10 may rotate about a substantially vertical axis when the yacht is in a normal disposition (i.e. the carrier may turn as shown by arrow A in Figure 1). The longitudinal support tube 11 supports a servo-rudder shaft 16 to the lower free end of which is attached a servo-rudder blade 17, and to the upper free end of which is attached a first crank having a slot 18. In the wind sensor shaft support tube 14 is rotatably carried a shaft 19 of a wind sensor 20, so that the shaft may turn about a substantially vertical axis, as shown by arrow B in Figure 1. Intermediate the end of the wind sensor shaft 19 there is adjustably mounted a second crank 21, which carries adjacent its free end a peg 22.The peg 22 lies on an axis which extends through the intersection of the axes of the wind sensor shaft support tube 14 and the longitudinal tube, and fits into the slot 18 of the first crank, thereby forming a proportional reversing linkage between the wind sensor shaft 19 and the servo-rudder shaft 16. The second crank 21 has a split bush (not shown) fitted therewithin, which bush can be clamped around or released from the wind sensor shaft 19 by turning a handle 23 journalled in the crank 21 and having an eccentric cam (also not shown) provided within the crank. The crank 21 may thus be fixed at a particular angular disposition relative to the shaft 19, and moreover the peg 22 may be disengaged from the slot 18 of the first crank by raising the second crank on the shaft 19. The wind sensor 20 comprises a vane 24 mounted on one end of a horizontal stem 25 fixed within a bore provided in a boss 26 attached to the upper end of the shaft 19. The end of the stem 25 remote from the vane 24 carries a counter-weight 28.

A generally horizontal cross-tree 29 is mounted on servo-support tube 11, and extends to either side of a point common to the axes of the longitudinal support tube 11 and the bearing tube 12. A pair of cords 30 are attached one to each end of the cross-tree 29, each cord 30 passing around one pulley respectively of a double concentric pulley 31 mounted adjacent the free end of the tiller arm 32 of the yacht, the cord then extending to a side of the yacht, there to be secured by a jamming cleat 33.

To set up the self-steering gear, the cords 30 are adjusted so that when the tiller arm 32 is directed along the centre line of the yacht, the plane ofthe carrier 10 lies in substantially the same direction. A bias could however be given to the gear by easing one ofthe cords and taking up the slack on the other.

To use the gear, the main rudder is set at an appropriate angle to the yacht axis to give the required heading, taking into account the wind direction, any tidal flow, and so on. Then, the handle 23 is turned to release the second crank 21, thereby to allow the wind sensor 20 align itself with the appar entwind.Atthe same time, the servo-rudder blade 17 will align itself with the apparent flow direction of the water beneath the stern. When the wind sensor 20 and the servo-rudder blade 17 have found their equilibrium positions, the handle 23 is turned to lock the second crank 21 to the wind sensor shaft 19, ensuring the peg 22 is engaged in the slot 18.

It will be appreciated that when the crank 21 and the shaft 19 are locked together, any turning movement of the wind sensor 20 is imparted to the servorudder shaft 16 via the proportional reversing linkage provided between the wind sensor shaft 19 and the servo-rudder shaft 16.

Once a course has been set, the correcting action of the self-steering gear operates as follows. If the yacht deviates to the port side of a selected course, the wind sensor 20 will turn in a clockwise direction (as viewed from above) and the rotation of the sensor 20 is transmitted via the first and second cranks to the servo-rudder blade 17 which is caused to turn in the anticlockwise direction. The servo-rudder blade 17 is thus brought out of alignment with the apparent flow direction of the water beneath the stern and there is thus a resultant force on the starboard face of the servo-rudder blade 17 which in turn results in a clockwise moment being imparted to the carrier 10. The carrier 10 thus turns in the clockwise direction, and as it does so causes the tiller 32 to turn in the anticlockwise direction.The yacht is then turned to starboard, and, as the yacht returns to the selected heading, so the angular displacement of the wind sensor 20 from its equilibrium position decreases, and therefore the corrective angular displacement of the tiller is decreased, until the wind sensor 20, and the servo-rudder blade 17 have both returned to their respective equilibrium positions.

Figures 2 and 3 illustrate two arrangements of self-steering gear of this invention wherein the configuration of the wind sensor has been modified from that employed in the embodiment illustrated in Figure 1. The construction of the carrier 10, servo rudder shaft 16 and their associated part is similar two that of the embodiment of Figure 1 and will not be described again here.

In the arrangement of Figure 2, the wind sensor 20 comprises a vane 35 which is mounted for pivotting movement about an axis c which is inclined at an acute angle to the horizontal (when the yacht is in a normal disposition). This type of wind sensor is well known in the art as a "flip-flop vane". In a similar manner as in the embodiment illustrated in Figure 1, the wind sensor 20 turns around an axis coincident with that of the bearing tube 12, and thus at all times the turning axis of the wind sensor 20 is fixed relative to the yacht. The movement of the wind sensor 20 is transmitted to the servo-rudder blade 17 by suitable means, for example, a proportional linkage system, a flexible drive, or a gear train.

In the arrangement illustrated in Figure 3, the wind sensor 20 is mounted on the stern of the yacht, rather than on the carrier 10 as was the case in the two previously-described embodiments. The wind sensor is mounted for rotation about an axis parallel to the axis of bearing tube 12. Suitable means are provided to transfer rotational movement of the wind sensor 20 to the servo-rudder blade 17.

Figure 4 illustrates an alternative arrangement for transmitting the movement of the carrier 10 to the tiller arm 32. In this arrangement, the longitudinal support tube 11 is provided with a radial spar 36 extending from the intersection of the axes of the longitudinal support tube 11 and the bearing tube 12. A cord 30 is attached to the spar 36 and completes a loop around four rectangular positioned pulleys 37. The cord 30 is attached to the tiller arm 32 to allow a reversing linkage between the movement of the spar 36 and the tiller arm 32.

Referring to Figures 5a and 5b there are shown details of wind sensors which may be employed in self-steering gear of this invention. Figure 5a illustrates a box vane which may be secured to the end of a stem 27 to form a wind sensor. The box vane 40 comprises two generally parallel planar side plates 41 which are spaced apart by wall sections 42, thus defining two rectangular slot-like passages through the vane.

Figure 5b illustrates anotherform of vane which comprises a pair of assymmetric aerofoil section side plates 43 which are mounted on a stem 27, by means of a wall 44, such that the overall configuration is slightly wedge shaped, being widest furthest from the stem 27. Extra lift is generated by the Venturi effect between the plates, giving enhanced sensitivity, whereas the wedge-shape increases the dynamic stability.

By using a dual element vane as illustrated in Figure 5a or in Figure 5b the overall structural size of the vane can be reduced, and vanes of greater strength and smaller weight can be obtained.

Although the self-steering gear has been described solely with reference to yachts provided with a tiller arm, it will of course be appreciated that the self-steering gearofthis invention may be readily be adapted for use on yachts wherein the rudder is controlled by a wheel.

Claims (26)

1. A self-steering gear for a yacht, comprising a servo-rudder blade attached to the lower end of a servo-rudder shaft mounted for rotation about its axis on a carrier, means for mounting the carrier to the stern of a yacht such that when so mounted and with the yacht in a normal attitude the carrier may turn about a second axis extending generally vertically and the servo-rudder shaft axis lies generally in a common plane with said second axis, the servorudder shaft extending rearwardly from and downwardly at an acute angle to said second axis, a wind vane sensor shaft mounted for rotation about a third axis substantially parallel to or co-incident with said second axis, coupling means drivingly interconnecting the servo-rudder shaft and the sensor shaft whereby turning movement of one shaft is imparted to the other shaft, a wind vane adapted to turn the sensor shaft in dependence upon the apparent wind direction, and rudder drive means adapted to allow transferofturning movement of the carrier about said second axis to the main rudder of the yacht when the gear is mounted on the yacht.

2. A self-sterring gear according to claim 1, wherein the wind-vane comprises a weather-cock device having a generally-horizontally extending arm provided with a weater-cock vane at one end thereof, the arm being directly attached to the sensor shaft to cause turning movement thereof upon a change in the apparent wind direction.

3. A self-steering gear according to claim 2, wherein the arm extends beyond its attachment to the sensor shaft and carries a counter-weight to balance the weight of the weather-cock vane.

4. A self steering gear according to claim 1, wherein the wind-vane is carried on a shaft mounted for rotation about a generally horizontal axis, the vane upstanding from the shaft and a relatively heavy weight being attached to a downwardly extending arm also attached to the shaft.

5. A self-steering gear according to claim 4, wherein means are provided to allow adjustment of the angle of the vane-supporting shaft, relative to the horizontal direction.

6. A self-steering gear according to any of the preceding claims, wherein the wind vane comprises two vane elements mounted side-by-side, each vane element being either a flat plate or an aero foil section of symmetric orassymetric shape.

7. A self-steering gear according to any of the preceding claims, wherein the coupling means is adjustable to allow the setting of a desired heading for a given apparent wind direction.

8. A self-steering gear according to any of the preceding claims, wherein the coupling means has a non-linear action.

9. A self-steering gear according to claim 8, wherein the coupling means is in the form of a pair of crank arms, one mounted on each shaft respectively and one crank arm having a peg which is received in a slot in the other crank arm.

10. A self-steering gear according to any of the preceding claims, wherein the carrier has a bearing tube in which is supported the servo-rudder shaft, the tube extending for substantially the whole length of the shaft from the servo-rudder blade to the coupling means.

11. A self-steering gear according to claim 10, wherein the carrier also comprises a further tube about the axis of which the carrier adapted to be rotatably mounted on a yacht, the bearing and furthertubes being fastened together with an appropriate spacing and with an appropriate acute angle therebetween.

12. A self-steering gear according to claim 11, wherein said acute angle is not more than 459

13. A self-steering gear according to claim 12, wherein said acute angle lies in the range of from 150 to 35".

14. A self-steering gear according to claim 13, wherein said acute angle is substantially 25 .

15. A self-steering gear according to any of claims 10 to 14, wherein the mounting means comprises a pair of arms each suitable for attachment to a yacht stern at one end and supporting a spindle at the other end thereof, which spindle extends vertically and has the further tube of the carrier journalled thereon.

16. A self-steering gear according to any of the preceding claims, wherein the sensor shaft is supported by and mounted in a tube forming a part of the carrier, to lie co-axial with the second axis.

17. A self-steering gear according to claim 16, wherein the end portion of the servo-rudder blade extends forwardly of the second axis, the coupling means being provided at the free end of the other end portion.

18. A self-steering gear according to any of the claims 1 to 15, wherein the sensor shaft is adapted to be mounted directly on a yacht to which the gear is to be attached, the servo-rudder shaft terminating at its upper end adjacent the sensor shaft for connec tionthereto by the coupling means.

19. A self-steering gear according to any of the preceding claims, wherein the comprises cords attached to a cross-tree or quadrant on the carrier, which cords are connectible to the tilller of a tillercontrolled yacht such that turning movement of the carrier will cause movement of the tiller in the required sense.

20. A self-steering gear according to claim 19, wherein the cross-tree has two arms extending transversely of the carrier and is attached to the bearing tube in which the servo-rudder shaft is mounted at a position along the length thereof where the axis thereof intersects the second axis.

21. A self-steering gear substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.

22. Awind-vane device for a self-steering gear, comprising a strut carrying at one end thereof two or more spaced wind-vane elements each disposed generally parallel to the or each other element and parallel to the length of the strut, each element being of essentially the same shape and area as the or each other element, the strut carrying at the other end thereof a counter-weight for the vane elements, and a mounting being provided partway between the ends of the strut to allow connection of the strut to a sensor shaft extending in a direction substantially normal to the length of the strut and parallel to the general planes of the vane elements.

23. A wind-vane device according to claim 22, wherein the vane elements and the counter-weight may be moveable along the length of the strut, to allow adjustment when in use of the force applied to the vane sensor shaft by the wind.

24. A wind vane device according to claim 22 or claim 23, wherein each vane element is of simple laminar form or is of a symmetric or assymetric aerofoil section.

25. A wind vane device according to any of claims 22 to 24, wherein the two elements (in the case of a two-element vane) or the outertwo elements (in the case of a multielement vane) are mounted at an angle of not substantially greater than 100 to one another with the parallel edges extending generally parallel to the sensor shaft when the vane is mounted thereon, and with the widest-spaced parallel edges furthest from the sen sorshaft.

26. A wind vane device according to claim 22 and substantially as hereinbefore described with reference to and as illustrated in Figures 5a and 5b of the accompanying drawings.