TITLE: WATERBORNE VESSEL WITH KEEL

DESCRIPTION

The present invention relates generally to a vessel for travelling on water, having an improved keel, and particularly, but not exclusively, to a sailing vessel having an improved keel .

It is known in the art to provide a sailing vessel having a hull with a fin keel which is configured to be pivoted (or canted) about a pivot axis within the hull, with pivotal movement causing a lower portion of the fin keel to be displaced substantially laterally relative to a longitudinal axis of the hull. In this way, the degree of heeling experienced by the vessel may be controlled by varying the lateral position of the ballast portion relative to the hull. Advantageously, this allows the vessel to sail in an upright position with significantly

more sail power being generated than would otherwise be possible with a conventional fixed fin keel, the latter requiring a significant heeling angle before the weight of the ballast generates a significant righting moment (at which point the sail will tend to become less effective) . Thus, significant speed benefits may be obtained by canting fin keels.

It is recognised in the art that there are structural problems associated with incorporating canting fin keels into a hull and the stresses they put on localised areas of the hull. There is an additional problem in that the hull housing the pivot point has to be sealed and kept watertight. Any damage to seals used for this purpose can result in the vessel sinking quickly, not least because the seals often have to be large in size in order to accommodate movement of the fin keel. Sailing vessels that use canting fin keels also require additional controls

(e.g. foils, fins or dagger boards) to recover some leeway resistance since canting of the keel acts to reduce its effectiveness. In addition, it is not normally possible to cant a fin keel more than 40 degrees from the centre line of the vessel with a conventionally-shaped hull.

The present applicants have identified the need for a an improved keel which overcomes or at least alleviates some of the problems associated with conventional canting keels.

In accordance with the present invention, there is provided a vessel for travelling on water, comprising: hull

means; and a keel comprising a member depending from the hull means, the member comprising: two limb parts each depending from a respective lateral side of the hull means, the two limb parts defining at least in part an enclosed flow path extending in a bow to stern direction; and a ballast portion located between the two limbs,- wherein the ballast portion is moveable laterally relative to a longitudinal axis of the hull means .

In this way, a vessel is provided having a keel which is adjustable to vary the angle of the ballast portion relative to the hull means to provide a cant-like effect. Advantageously, the keel is attached to the hull means at two discrete points to provide additional structural rigidity to both the keel and the hull means, and to allow the load on the hull means to be shared by two parts thereof. In addition, the present invention obviates or at least alleviates the need for any additional fins, foils or dagger boards as the leeway resistance provided by the loop keel is substantially unaffected by movement of the ballast portion since the lateral projection of a loop keel (i.e. the part available to resist leeway) will remain substantially constant even when the loop keel itself is moved relative to the hull means.

In one embodiment, the ballast portion contributes at least 20% of the keel's mass. For example, the ballast portion may contribute at least 30% of the keel's mass.

In one embodiment, the ballast portion is moveable relative to the two limb parts. In this way, lateral

movement of the ballast means is achievable without movement of either limb, thereby allowing the keel to be rigidly coupled to the hull means. For example, the ballast portion may be moveably coupled to the limb parts. In another embodiment, at least one limb part is moveable relative to the hull means with the ballast portion being coupled to the at least one limb part. For example, the two limb parts may be coupled (e.g. rigidly coupled) to the ballast portion, whereby movement (e.g. rotation) of the member causes lateral movement of the ballast portion relative to the longitudinal axis of the hull means.

The two limbs may be configured to meet the hull means at upper parts of the hull means. In this way, the ballast portion may be configured to be moveable from one lateral side of the hull means to the other. The limbs may define a circular path, in which case the ballast portion may rotate through about 270 degrees around the path when travelling from one side of the hull means to the other. The upper parts of the hull means may lie above the water line of the vessel when in an upright position. In this way, there is a reduced risk of the hull means taking in water when a seal is damaged. Alternatively, the limbs may extend through the hull into respective chambers which extend above the waterline when the vessel is in an upright position. The limbs may engage a mounting (e.g. keel box) which is located above the waterline when the vessel is in an upright position.

In one embodiment, the two limb parts may each comprise a convex outer profile. For example, the two limb parts may together substantially form an arc.

Advantageously, such a loop keel maintains the same lateral projection regardless of its rotational orientation relative to the hull means. Accordingly, the leeway resistance of such a loop keel is substantially unaffected by rotation of the loop keel (e.g. about its centre point) .

Such a keel may also provide the following additional benefits:

1) Improved flow area to wetted surface area;

2) Improved structural strength;

3) Simplified fabrication and installation; and

4) Readily rotatable relative to the hull means. In the case of a sailing vessel, the two limb parts may be coupled to load-bearing parts of the sail assembly

(e.g. shrouds associated with a mast of the sailing vessel) . In this way, the loads produced by the keel may be used to stabilise the sail assembly. The ballast portion may comprise a ballast bulb.

In one embodiment, the two limb parts each have a zero-lift surface which is angled to generate in use a component of hydrodynamic force directed away from the enclosed flow path when there is a net flow of water incident in the bow to stern direction.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 shows a schematic front view of a sailing vessel according to the present invention in a first configuration; and

Figure 2 shows a schematic front view of the sailing vessel of Figure 1 in a second configuration.

As shown in Figures 1 and 2, sailing vessel 10 comprises a hull 20 and a loop keel 30, the loop keel 30 comprising a looped keel member 34 rigidly attached to the hull 20 at two laterally spaced locations 38,39 above the waterline of the hull. The looped keel member 34 comprises a pair of limb parts 44,45 joined to form a continuous arcuate track 50 onto which a ballast bulb 42 is moveably mounted.

The ballast bulb 42 is moveable along the track 50 to vary its position relative to a longitudinal axis

(extending in a bow to stern direction) of the hull 20 (in the case of the illustrated example, the longitudinal axis extends perpendicularly to the plane of the page) . The position of the ballast bulb 42 may be secured using a cog and gear mechanism (not shown) . The ballast bulb is moveable between a first (central) position and a second

(laterally offset) position. The ballast bulb may move to a yet further laterally offset position (e.g. adjacent one or other of the laterally spaced locations 38,39). The pair of limb parts 44 in combination with the hull 20, form an enclosed flow path (a "loop" or aperture) 40 through which water may pass. The limb parts 44,45 comprise inner and outer surfaces 44a, 44b and 45a, 45b

respectively which are configured .so as to generate a continuous outwards force all around the loop (this is directly equivalent to a vortex ring in a continuous flow) . For example, the limb parts 44,45 may have a cambered or uncambered foil profile having a zero lift surface which is angled to generate a component of hydrodynamic force directed away from the enclosed flow path 40 when the loop keel 30 passes through incident water. The loop keel 30 provides many advantages over conventional fin keels, including a reduction in drag due to low vorticity being shed by the loop. In addition, if the vessel should in use experience a significant heel angle such that part of one limb is partially clear of, and above the water surface, the other, lowest limb, by virtue of the angling of the zero-lift surface, generates a righting moment (assuming forward motion of the vessel is present) . At lower angles of heel, the forces on the limbs of the loop will tend to force water to fill or partially fill the loop even when the loop is partially above the water surface. This manifestation of the added mass effect also now forms an additional dynamic ballast element in that the water within the loop that has been raised above the static waterline is now providing a weight-derived righting moment acting directly on the keel members . Any roll disturbance of the keel under forward motion may therefore generate a substantial righting moment .