GB2177353A - Boat keel - Google Patents

Abstract

A boat hull (10) has a keel (11) having a pair of side foils (12) descending from both sides of the hull (10), below the water-line (13), to a junction (14) below the centre line of the hull (10). The side foils (12) may curve convergently downwards to join with a central foil (15). Each foil (12, 15) decreases in width from top to bottom and is of streamlined or aerofoil cross-sectional configuration. Ballast may be fixed at the junction of the foils. The keel (11) imparts a uniform horizontal velocity to the water within the region of the keel (11) when the boat is in motion and thereby lateral force to oppose the lateral force on the boat's sails. In an alternative embodiment, side foils extend convergently downwards to a transverse bottom foil. <IMAGE>

Description

SPECIFICATION An improved boat keel BACKGROUND OF THE INVENTION (1) Field of the Invention This invention relates to an improved boat keel.

(2) Prior Art The keel or centre-board of a sailing boat is in some respects analogous to the wing of an aeroplane; whereas the wing generates lift by its forward motion, the keel generates lateral force to resist the opposing lateral force on.

the boat's sails.

A typical keel, however, is considerably less efficient than a typical wing. The efficiency of an aeroplane wing is measured by the lift/drag ratio, typically of the order of 20 to 50; but the efficiency of a conventional boat keel is of the order of about 5. The inefficiency of the keel is not due to skin friction or to form drag, but to induced drag which results in large-scale movement of the water, skin friction and form drag resulting mainly in different degrees of turbulence. With an aircraft, the induced drag may be reduced by designing for a larger aspect ratio by increasing the wingspan, but with a sailing boat the analogous remedy, of making the keel deeper, is not generally available as it would aggravate the heeling problem in light craft, it would make shallow waters inaccessible and, in the case of a formula racing boat, it would attract penalties.

SUMMARY OF THE PRESENT INVENTION The present invention has been devised with the general object of providing a boat keel which is particularly efficient in operation.

Accordingly, the invention resides broadly in a boat keel including a pair of side foils converging symmetrically downwards from corresponding positions at opposite sides of the boat hull and co-joined below the centre-line of the hull. The side foils are preferably of streamlined or aerofoil cross-sectional configuration. Preferably one ar more intermediate foils extend down from the hull bottom to the side foils or to their junction.

Other preferred features of the invention will become apparent from the following description.

BRIEF DESCRIPTION OF THE DRA WINGS Various embodiments of the invention are shown, by way of illustrative example only, in the accompanying drawings, wherein: Figure 1 is a side elevational view of a sailing boat with a keel according to one embodiment of the invention, Figure 2 is a front elevational view of the boat shown in Fig. 1; Figure 3 is a perspective view of the boat from below, Figure 4 is a sectional view, to larger scale, taken along any of the lines 4-4 in Fig. 2, and Figures 5 and 6 are midship sections of boat hulls with keels according to further embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring initially to Figs. 1 to 4 inclusive of the drawings, a sailing boat hull 10 of generally conventional lines except for the configuration of its keel 11. This keel comprises two side foils 12 descending from both sides of the hull 10, from corresponding positions somewhat below its waterline 13, to curve convergently downwards to join at a junction 14 with the bottom of a central foil 15 extending downwardly from the bottom centreline of the hull. Each of the side foils 12 and the central foil 15 decreases somewhat in width from top to bottom and, as shown in Fig. 4, is of streamlined cross-sectional configuration.

The keel assembly, then, although of no undue depth whether the boat is upright or heeled, has a very considerable effective length without the disadvantages of likelihood of fouling a jetty or river bank when moored.

These considerations define an "available region" below the boat's water line within which the whole of the keel should be contained. It is believed that the keel according to the invention will be very effective in imparting to the whole of the water within the "available region" a suitable uniform horizontal velocity when the boat is in motion.

The boundary of the "available region" will be a discontinuity of velocity, or vortex sheet coming from the tapered trailing edges of the side foils 12. The central foil 15 structurally reinforces the keel assembly and should not increase induced drag or generate a vortex sheet at its trailing edge.

The boat shown in midship section in Fig. 5 is of shallow draught river-boat type. From corresponding locations at both sides of its hull 20, somewhat below the water line 21, side foils 22 extend convergently downwards and are connected by a transverse bottom foil section 23, two intermediate and laterally spaced foils 24 extend from the hull bottom to be rigidly connected to this bottom section 23.

The embodiment of Fig. 6 is applicable to a deep-sea boat, the hull 30 of which has a keel comprising two side foils 31 which are substantially straight, and which are convergent downwards to a junction at 32, where the ballast is fixed, no central or intermediate foils being included in this embodiment.

Keels according to the invention will be found to be very effective in achieving the objects for which they have been devised. It will, of course, be understood that many modifications of constructional detail and design, which will be readily apparent to persons skilled in the art, may be made within the scope and ambit of the invention defined in the appended claims.

Claims (1)

1. A boat keel including a pair of side foils converging symmetrically downwards from corresponding positions at opposite sides of the boat hull and co-joined below the centreline of the hull.

2. A boat hull as claimed in claim 1 wherein: the side foils are of streamlined or aerofoil cross-sectional configuration.

3. A boat hull as claimed in claim 1 or claim 2 wherein: one or more intermediate foils extend down from the hull bottom to the side foils or to their junction.

4. A boat hull as claimed in any one of claims 1 to 3 wherein: the side foils decrease in width from top to bottom.

5. A boat hull as claimed in any one of claims 1 to 4 wherein: the side foils curve convergently downwards to the junction.

6. A boat hull as claimed in any one of claims 1 to 5 wherein: the side foils extend convergently downwards and are connected by a transverse substantially horizontal bottom foil section.

7. A boat hull as claimed in claim 6 wherein: two or more intermediate and laterally spaced foils extend from the hull bottom and are rigidly connected to the bottom foil section.

8. A boat hull as claimed in claim 1 wherein: ballast is fixed to the junction of the side foils.

9. A boat hull substantially as hereinbefore described with reference to Figs. 1 to 4, or Fig. 5, or Fig. 6 of the accompanying drawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1 and 2 above have been deleted or textually amended.

New or textually amended claims have been filed as follows:

1. A boat keel including a pair of side foils converging symmetrically downwards from corresponding positions at opposite sides of the boat keel and co-joined below the centre line of the hull, said side foils being of streamlined or aerofoil cross-sectional configuration.

Claims 3-9 above have been re-numbered as 2-8 and their appendancies corrected.