GB2270040A - Sailing vessels - Google Patents

Abstract

In order to permit a yacht to sail more upright, while permitting the mass of its keel ballast 4 to be significantly reduced, the force of the water flowing past the keel is used to generate a lateral force on the keel in the appropriate sense to push the boat upright. The force is generated by providing the lower end of the keel with a member 6 which is steerable via a shaft 8, and/or which may have its cross-sectional shape changed, as by a cranked cam 20 to provide a hydrodynamic righting force. Alternatively or additionally, the rudder may be able to have its cross-sectional shape changed so that its lateral force is a function of both angle of deflection and hydrodynamic shape. <IMAGE>

Description

SAILING VESSELS This invention relates to sailing vessels, particularly to the keels thereof.

In this specification, the term 'keel' could cover centreboards and daggerboards for dinghies, but the invention is primarily applicable to the fixed keels of yachts, and to their rudders.

Unlike dinghies, in which the lateral forces applied by the wind to the sails are intended to be partially counterbalanced by the lateral positioning of at least one member of the crew, in yachts these lateral forces are counterbalanced primarily by heavy weights attached to the bottoms of the keels. In this way, the pull of gravity on the keel weights is split into a reduced downward force on the centre line of the yacht, and a perpendicular force on the bottom of the keel tending to push the yacht upright against the force of the wind.

The positioning of a very heavy-weight at the bottom of the keel applies significant stresses to the rest of the yacht structure, requiring the hull to be made strong enough to absorb these stresses, adding to the cost thereof. In addition, the passive action of the keel weight (or 'ballast', as it is usually called) in righting the vessel comes into play only when the vessel is heeled.

The present invention aims at enabling ballast weights to be significantly reduced without degrading a vessel's sailing performance, and at providing some lateral righting forces on the keel which are independent of the angle of heel.

In its broadest aspect, the present invention provides an underwater control member for a sailing vessel, which is adapted to cause the water through which the control member passes to apply a differential lateral force on the control member, the force being adjustable as a function of the angle of attack of the control member; of the cross-sectional shape of the hydrofoil formed by the control member, or of a combination of both angle and shape.

In another aspect, the present invention provides a sailing vessel with a keel having a zero angle of attack and of which the major side surfaces may have their curvature adjusted differentially so as to provide an adjustable force on the keel laterally of its direction of movement through the water.

In yet another aspect, the present invention provides a sailing vessel with a control member which is pivotable about an axis lying in the centre plane of the vessel, the cross-section shape of the control member being adjustable as a function of the angle through which the member has been pivoted out of the centre plane.

The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view showing how the righting force on a sailing vessel is generated by its angle of heel; Figure 2 is a diagrammatic side elevation of a yacht fitted with a keel in accordance with the present invention; Figure 3 shows a diagrammatic oblique view of an active keel of the present invention with the external surfaces thereof removed to show the internal construction; Figure 4 is a cross section on line IV-IV of Figure 2; Figure 5 are diagrammatic scrap views of parts of the two sheets forming the trail edge of the active keel of Figures 2 to 4; Figure 6 is a diagrammatic view, similar to Figure 4, to illustrate the mode of operation of the active keel;; Figure 7 is a diagrammatic side elevation of a yacht fitted with a fixed keel of adjustable cross sectional shape to provide adjustable righting forces; Figure 8 is a diagrammatic part-skeletal, oblique view of the keel of Figure 7, showing its internal construction; Figure 9 is a diagrammatic cross-section on the line IX-IX of Figure 7; Figure 10 is a diagrammatic side elevation of a yacht fitted with a rudder of the present invention, and Figure 11 is an enlarged section of the rudder along the line XI-XI of Figure 10.

As shown in Figure 4, a sailing vessel having a mass of about 10,000 kg needs a ballast weighing about 4,000 kg in order to generate a righting force which is proportional to the angle of heel. In the example shown, when the yacht is heeling through 200, the gravitational force of 4,000 kg on the ballast gives rise to a component of 1,200 kg acting laterally on the keel. In accordance with the present invention, this righting force is generated by a combination of gravitational force on a ballast of less weight, combined with a hydrodynamic force which is generated by movement of the vessel through the water, and independent of its angle of heel.

Figure 2 shows the hull 2 of a sailing vessel having projecting from it a stub keel 4 having an integral ballast of reduced weight, say of 2,000 kg for a vessel of water line length 18 m. Projecting from the bottom of stub keel 4 is a relatively-short length of active keel 6. This has the hydrofoil section shown in Figure 4, and is pivotable about an axis of a shaft 8 spaced inwardly a short distance from the leading edge 10 of the active keel. The keel is rotated about the axis by means of shaft 8 movable with keel 6 and journaled in keel 4, terminating at its upper end in an arm 12 by which it can be pivoted, either manually or mechanically.The arm 12 could be acted on by an automatic helming device operating on the servo-control principle, but the manner in which the lever is operated does not form part of the subject-matter of this invention and so will not be described herein in any further detail.

Because the active keel 6 has a hydrofoil cross-section, it functions to provide lateral force when its centre line is at an angle to the direction of water flow past the keel. In known fashion, this lateral force is constituted of two components. The lesser component is the pressure generated by the water bearing on the surface of the active keel exposed to the flow of water.

The greater component of the lateral force is generated by the suction exerted on the 'downstream' face of the active keel as a result of acceleration of the water flow over this bowed surface, because of its greater length.

Obviously the active keel will have some mass, but this will have a negligible ballasting effect, because of the undesirability of requiring the arm 12 to pivot a significant weight. However, in the case of an active keel of fixed shape, it might be acceptable to make the active keel solid and of relatively-massive construction.

It is preferred for most of the ballast to be in the form of a streamlined 'bulb' integral with the keel, or otherwise positioned below the active keel.

In that version of the invention shown in Figure 2 to 6, the cross-sectional shape of the active keel 6 is adjustable. To this end, the leading edge 10 of the keel is provided by a longitudinal former 14 to which are secured two sheets 16 (or a double-length folded single sheet) of flexible material, such as stainless steel, which sheets meet at the trailing edge 18, being held there in a manner which permits them to slide over one another to accommodate differential flexure of the sheets. Because it would be counterproductive to give the active keel buoyancy, it is envisaged that the interior of the keel would be able to be filled with water, but access of the water to the interior of the keel would be through filters designed to keep out seaweed and living organisms, such as barnacles, while permitting air to be displaced from the interior of the keel.The two sheets 16 (or folded single sheet) are held in contact with a cranked cam 20 by their built-in curvature and natural elasticity at a position spaced rearwardly of the shaft 8 to which the keel is fast and which is intended to be pivoted by arm 12. The cam 20 extends into the interior of the keel 6 from the stub keel 4. As the active keel 6 has its angle of incidence (attack) to the centre line 24 of the yacht changed, the sheets 16 come into contact with the cam which displaces sides 16 differentially to produce a lateral righting force additional to that produced merely by the change in the angle of incidence of the active keel to the ambient water. As shown in Figure 6, the upstream sheet has its amount of curvature reduced, whereas the downstream sheet has its curvature increased. This produces a combined lateral force on the active keel substantially at right angles to its axis. This combined force is resolved into a righting force at right angles to the centre line 24, and increased drag along the centre line.

As shown in Figure 5, the two sheets or sides 16 have their trailing edges 18 provided with a series of spacedapart dovetail-sectioned sliders 22, with the sliders being bolted or otherwise secured to the inner surface of the respective sheet. The two sets of sliders are interdigitated so as to stop the ends of the sheets from moving apart laterally, but leaving them free to slide relatively to each other to accommodate their length differential as the curvature of each sheet is reduced or increased by its contact with cam 20.Although not shown in Figure 5, as already mentioned, the coupling between the two sheets at the trailing end 18 thereof would normally be protected by a filter (not shown) to allow entry into the interior of the active keel of only water, so that the sliding surfaces and other internal parts are of the active keel do not become choked by internal deposits or growths.

In that version of the invention shown in Figures 7 to 9, the active keel is dispensed with, but instead at least the lower end of the keel above the bulb is designed to produce a controllable righting force dependent on its speed through the water by varying the cross-sectional shape of the keel. To this end, the keel is made of hollow construction similar to the active keel of Figures 2 to 6. It uses static formers 24 and 26, to the former of which a single piece of folded stainless steel sheet, or two separate pieces of sheet, are secured by a longitudinal series of bolts 28. Positioned between the formers 24 and 26, and in the space between the sheets 16, are two rotary cams 30 (although a single cam would suffice for a small keel).The two cams are of similar cross-sectional shape, and are connected together by a link 32 so that they move in unison when the control shaft 34 is pivoted. Such pivotal movement leads to the curvature of one sheet 16 being reduced, and that of the other sheet increased, as discussed above, so as to give a lateral force on the keel arising from an unbalanced hydrodynamic force. It is envisaged that no means would be necessary to ensure that each sheet resiles from its position of greater curvature when the cams 30 are moved back to their neutral position shown in full lines in Figure 9, but if it were necessary, then it is envisaged that some elastomeric bias could be applied between the rear former 26 and the sliders 22 at the trail ends of sheets 16, in order to bias both sheets to the positions in which they are each in contact with both cams 30.

That embodiment of the invention shown in Figures 10 and 11 relates to a rudder of adjustable cross-sectional shape so that a lateral force can be applied to the rudder as a function of both its angle of attack to the flow of ambient water and to the unbalanced hydrodynamic forces already described with respect to the other two embodiments of the invention. In this version of the invention, the two sheets 16 are engaged by a cam 30 fixed to the hull. As the rudder changes its angle of attack with respect to the relative flow of water, by pivotal movement of shaft 36, functioning as the rudder post, the sheets 16 are constrained to adopt a hydrofoil giving a lateral force on the rudder additional to that supplied merely by pressure of water on the upstream face of the rudder.

Although not shown in any of the drawings, it might also be sound practice to equip the lower end of the active keel of Figures 2 to 6, or the adjustable hydrofoil keel of Figures 7 to 9, with a collision absorber or solid bulb ballast weight which would act as a sacrificial body which is intended to be abraded preferentially to the rest of the keel should the keel come into accidental or deliberate contact with the sea bed or underwater obstructions.

It should be possible to generate 1,000 to 1,500 kg of righting moment per square metre of the elevational area of the active keel at a boat speed of about six knots.

This can be compared with the righting force of about 1,200 kg provided by a 4,000 kg ballast at heel angle of 200 (which increases to 2,000 kg at 300 heel).

If half the designed ballast weight is retained for stability when the boat is static or moving at only low speeds relative to the water, then about 500 kg of 'righting' force is required, which could be provided by an active keel having an effective area of about 0.5 square metres.

Accordingly it will be seen that the present invention provides apparatus by which a boat can be sailed virtually upright irrespective of the ballast weight and of the wind speed, thus leading to sailing vessels of lighter, and therefore cheaper, construction, and to more-efficient use of the sailing rig.

Claims (3)

1. An underwater control member for a sailing vessel, which is adapted to cause the water through which the control member passes to apply a differential lateral force on the control member, the force being adjustable as a function of the angle of attack of the control member; of the cross-sectional shape of the hydrofoil formed by the control member, or of a combination of both angle and shape.

2. A sailing vessel with a keel having a zero angle of attack and of which the major side surfaces may have their curvature adjusted differentially so as to provide an adjustable force on the keel laterally of its direction of movement through the water.

3. A sailing vessel with a control member, such as a keel or rudder, which is pivotable about an axis lying in the centre plane of the vessel, the cross sectional shape of the control member being adjustable as a function of the angle through which the member has been pivoted from the centre plane.