This invention relates to a rudder for marine vessels.

In marine vessels the, or each, rudder is made large enough in area to balance the forces applied to the vessel by the sail or other motive system. To reduce the helm forces which a helmsman needs to provide in order to control and steer the vessel when sailing ahead, the axis of the steering shaft of a rudder is usually .arranged so that up to 20% of the area of the rudder lies upstream of this axis, and the remainder downstream. The centre of pressure of the rudder, typically lying at 25% to 30% of the chord length downstream from the leading edge thus lies closely abaft the axis, and the resulting rudder torque is held at a low value.

When manoeuvring astern the centre of pressure shifts to a zone about 25% from the original trailing edge, which for such a manoeuvre becomes the new leading edge, resulting in high values of rudder torque around the steering shaft. The resulting large helm moments may be reacted on to the steering system. This means that control going astern may be seriously impaired, and in extreme cases the rudder stops may be damaged or injury to the helmsman may occur.

In balanced ships' rudders mechanisms have been devised that enable the rudder to be moved forwards when it is desired to reverse the vessel.

Such a mechanism is shown in the UK specification 259,831, but has the disadvantages of requiring a framework to support the mechanism which although acceptable on larger vessels does not readily adapt for use on smaller vessels.

Another problem that occurs especially with smaller vessels, is that the rudder has the greatest underwater projection of the vessel and can be fouled in shallow water. To overcome this problem various 'kick up' rudders have been proposed in which the rudder pivots abaft to a shallower configuration.

The present invention addresses both these problems and provides a 'kick up' type of rudder that also incorporates a balancing mechanism.

Accordingly the present invention provides a steering device for marine vessels comprising a blade pivotable about a first axis to provide steering and upwardly pivotable about a second axis to adopt a configuration having reduced draft and in which the blade has means providing a limited range of movement forwards and abaft with respect to said first axis for positioning the acting centre of pressure of the blade with respect to the first axis for different directions of motion of the vessel.

The invention will now be described by way of example with reference to the accompanying drawings in which:-

Figures 1 to 4 illustrate a prior art rudder;

Figure 5 shows schematically a side view of one embodiment of the rudder according to this invention;

Figure 6 shows the rudder of Figure 5 when the vessel is sailing ahead;

Figure 7 shows the rudder of Figure 5 when the vessel is sailing astern;

Figure 8 shows a vertical section taken perpendicular to Figure 5;

Figure 9 shows detail of a lost motion connection on the rudder;

Figures 10 to 13 show enlarged views of various possible positions of a lost motion constraint in the embodiment of the invention shown in Figure 9.

In Figure 1 a rudder blade 1 is pivotably mounted on a rudder steering shaft 2 passing through a bearing 3, set into the hull 4 of a marine vessel. The vessel is shown as proceeding ahead in the direction of the arrow 5, and the resultant relative water flow direction is indicated by the arrow 6.

The steering shaft has an axis 7 which is conventionally set so that it passes through the rudder just upstream of the centre of pressure zone 8.

In the view drawn in Figure 2, showing a cross-sectional view taken perpendicular to the axis 7, it can be seen that the rudder force indicated by arrow 9 passing through the centre of pressure zone 8, and the small moment arm 10 through which the force 9 acts about the axis 7, combine to produce small, acceptable levels of torque which react on the rudder steering shaft, and thus on the rudder operating system as a whole.

In Figures 3 and 4 the direction of the vessel's motion is reversed such that it now moves astern in the direction of the arrow 11. The resultant relative water flow direction is thus as indicated by the arrow 11a.

The centre of pressure zone has now moved to position 12, and as shown in Figure 4, the rudder force represented by arrow 13 is now acting about the axis with a longer moment arm 14. Much larger torques may therefore be reacted through the rudder steering shaft and transmitted to the steering system when the vessel is moving astern.

In Figures 5 to 8 a similar hull 4 also has a rudder bearing 3 but in this case the rudder steering shaft terminates in a forked stock 26, in which a rudder blade 27 is freely pivoted perpendicular to the rudder steering axis 7 on a pin 28. Its range of movement in the pivotal sense is constrained by a second pin 33, fixed through the blade working in apertures on plates 34 on each side of the rudder blade. The pin 28 is offset aftwards with respect to the pin 33. The two possible centre of pressure zones are indicated as position 20, where the centre of pressure zone occurs when sailing ahead, and at position 21 when sailing astern.

In Figure 6, the vessel is shown sailing ahead, as indicated by the arrow 22, and the relative water flow is as indicated by arrow 23. The water resistance has caused the blade 27 to pivot about the pin 28 and move astern as far as is permitted by the pin 33 and its co-operating restraint (described later) . The rudder force produced when the rudder is operated acts through the centre of pressure zone 20 when sailing ahead, and an acceptable level of torque is transmitted to the steering system, since the length of the moment arm 40 around which the rudder force acts is kept short.

In Figure 7, the same vessel is shown sailing astern, as indicated by the arrow 24, and the relative water flow is as indicated by arrow 25. The water resistance has caused the

blade 27 to move until the pin 33 abuts against the forward end of its restraint. The rudder force now acts through the astern centre of pressure zone 21, and an acceptable level of torque is once more transmitted to the steering system, since the length of the moment arm 41 around which the rudder force acts is still kept short as shown.

The arrangement shown in Figures 5 to 8 also enables retraction of the rudder blade to permit sailing in shallow water or enable grounding of the vessel on sand or mud without damage to the rudder. For this purpose, the steering shaft is hollow, and a rod 30 can move up and down inside it under the command of an actuator 31, indicated diagrammatically as a hydraulic cylinder. At the lower end of rod 30 is a crosshead assembly, comprising a large boss 32 and the crosspin 33.

In this particular embodiment the two plates 34 are integrated into the blade structure and specially shaped apertures 38 (shown in Figures 9 to 13) in the plates 34 permit a degree of movement vertically as well as that utilised laterally to enable the swinging described for Figures 6 and 7. Operation of the actuator 31, so as to move the rod 30 downwards, therefore rotates the blade 27 about the pin 28 in the direction of the arrow 35 and retracts it to a position indicated by the broken outline 36, swinging the blade through an angle of approximately 90 degrees, thus reducing the depth of water needed for safe sailing. The dot-dashed line 37 indicates a reference line on the blade passing through pin 28 and the ahead centre of pressure zone 20.

Figure 8 is a sectional view taken in a plane at right angles to the plane of symmetry of the rudder blade, and parallel to and passing through the rudder axis. It shows

the two plates 34 and the pin 33 which passes through both plates. The feet, or fins 39 shown extending at right angles to the forked stock 26 may be helpful in providing a foot for supporting the vessel when grounded, and can also act as hydrodynamic fences.

The particular arrangement of free play allowed in the relationship between the pin 33 and the specially shaped apertures in plates 34 is now described referring to Figures 9 to 13 inclusive.

Figure 9 shows an aperture 38 in relation to the rudder and pivot 28. Figures 10 to 13 are enlarged views on the outer side of a plate 34, showing an end of the pin 33 and an end of the blade pivot pin 28. As before, the dot-dashed line 37 indicates the reference line on the blade passing through pin 28 and the ahead centre of pressure zone 20 (see Figure 5) . Alternative arrangements to apertured plates, such as grooves or pivotal constraint mechanisms may be incorporated.

The pin 33 works in an aperture 38, which is duplicated in both plates 34. This aperture has a substantially triangular shape with rounded apices which are shaped to co-operate with the pin 33. The outline of the crosshead boss 32 is indicated by a chain dotted line, since it is in fact out of sight between the plates 34.

The movement of the pin in the aperture 38 as it is moved downwardly with respect to the pivot pin 28 is described with reference to Figures 10 to 13. In Figure 10 the pin 33 is at its highest position, having pulled the upper part of the rudder anticlockwise as shown, so that the centre line of the rudder, indicated by line 37, is angled rearwardly in the general alignment required for sailing ahead. As shown,

the rudder is prevented by the abutment of pin 33 against the upper (as viewed) apex of the aperture 38 from moving in a clockwise direction as viewed about pivot 28. A side 40 of the aperture is shaped as an arc centred on pivot 28, and thus limited pivoting movement of the rudder, constrained by the apices at the ends of side 40 is provided. In the drawing the rudder is shown at the clockwise (as viewed) limit of pivotal movement, but anticlockwise pivoting is possible.

When the vessel sails astern the pin 33 abuts the other limit of permitted pivoting as shown in Figure 11. In both Figures 10 and 11 the full outline of pin 33 shows its relative position in aperture 38 and the dotted outline shows the apex at the other limit of pivoting movement, although it should be noted that it is the rudder and plate that move to provide this relative movement, not the pin 33.

Downward movement of the pin 33 itself is used to bring about larger clockwise (as viewed) rotation of the rudder. In this instance, the pin 33 moves vertically downwards and the separation between the pin 33 and pivot 28 reduces from the distance as shown in Figures 10 and 11 to the position of closest approach, shown in Figure 12. If the vessel is sailing ahead during this movement, water flow will have rotated the rudder clockwise, and so the pin 33 will (relatively speaking) traverse along a straight edge 41 of the aperture 38 to the position shown in Figure 12, and then further downward movement will cause the pin 33 to move along a second straight edge 42 of the aperture 38, continuing to rotate the rudder in the clockwise direction until the pin locates in the apex between sides 40 and 42 in the position shown in Figure 12, when the rudder is fully retracted.

In the event that the vessel is stationary, or moving astern, when downward movement of the pin 33 takes place the initial position of the pin 33 in the aperture will be different. If the vessel is stationary, then the rudder may adopt a vertical position (as shown in Figure 5) and the pin 33 will be somewhere along side 40 in the range of movement between the Figure 10 and Figure 11 positions. Downward movement of the pin 33 will then first move the pin straight down in the aperture until it engages with side 42 after which as the pin moves further downwards the aperture will move with clockwise rudder rotation, the side 42 sliding against the pin until the configuration of Figure 11 is reached, and then movement to the Figure 12 position is as described earlier.

When the vessel is moving astern, the starting position is as shown in Figure 11 and during the entire downward movement the pin slides against side 42, as the rudder is rotated clockwise.

When the rudder is retracted the two feet or fins 39 (see Figure 8), which may be provided on the forked stock, project below the leading edge of the retracted blade, and may help to support the weight of the after end of the vessel if it is grounded, while protecting the blade in this situation or when sailing in shallow water.

Note that in all cases the crosshead boss 32 is of sufficient size to entirely cover the aperture 38, and thus to minimise contamination of the mechanism by (for example) mud, sand and marine growths. A particular feature of this embodiment of the invention is that a full excursion of the pin 33 from one extreme of its travel to the other, should suffice to clear away any accumulation of such debris. Further, if the blade were to jam in either the ahead

sailing position when going astern, or vice versa, and the water drag were insufficient to correct the situation alone, a short excursion of the pin 33 should in either case suffice to free the blade and restore the rudder torque to its correct level.