GB2114515A - Sailing yacht - Google Patents

Abstract

The keel (2) of a sailing yacht is provided with at least one fin (5) on each side of the keel towards its tip. The fins act to improve the side force and lift characteristics of the keel. <IMAGE>

Description

SPECIFICATION Sailing yacht The present invention relates to a sailing yacht with, as usual, a keel below the hull.

Such a keel has the function to improve the stability of the yacht and its windward sailing performance by producing hydrodynamic side force opposing the side force on the sails, thereby preventing the yacht from making leeway.

The present invention aims to further improve the side force and lift characteristics of the keel.

This is obtained in that the keel in the vicinity of the tip on each side of the keel is provided with at least one fin.

From tests it appeared that in this way substantial improvement in side force and lift characteristics can be obtained.

The invention will be described with reference to the schematic drawings, in which: Figure 1 shows a side view of a part of the hull, the keel and a fin; Figure 2 shows a bottom view of the same; and Figure 3 shows a rear view of the same as a somewhat greater scale.

The hull 1 of the yacht is as usual provided with a keel 2 and a rudder 3. The waterline is indicated with 4. The fins are indicated with 5 and can be incorporated in any keel but preferably to one having an inverse taper i.e. the length of the keel increases in a downward direction. The fins have an aerofoil or stream-lined cross-sectional shape.

The present invention comprises two fins 5 incorporated in a keel 2 one fin being positioned on each side of the tip of the keel 2 at an angle of between 0 and 45" to the perpendicular plane of the keel 2 in a downward direction.

The incorporation of the fins 5 improves the side force or lift production of the keel.

The physical mechanism responsible for the generation of lift is that of vortex shedding. On three-dimensional bodies vorticity is shed wherever the boundary layer separates from the body. Hulltype bodies are generally designed so as to avoid any vortex shedding i.e. boundary layer separation at all. As a result, such bodies produce very little lift or side force of their own. A keel fitted to a hull produces a greater amount of lift or side force. If the fins are incorporated in a keel a far greater amount of lift or side force is generated.

During movement of the yacht through the water the tip vortex of the keel is moved away by the fins from the plane of the keel, thereby reducing the downwash caused by the keel and hence increasing the left and,or decreasing the vortex drag of the keel.

Because the reduction in downwash is the greater near the tip of the keel, the fins are most effective near that region.

Another advantage of a keel which incorporates fins is that the span or draught of the keel increases with the angle of heel.

Preferably the foot of each fin 5 has a width which is more than 30% of the width of the tip of the keel.

By applying fins it is further possible to lower the centre of gravity of the ballast-weight which means an increasement of the stability.

1. A sailing yacht having a keel below its hull in which the keel, in the vicinity of the tip, and on each side of the keel, is provided with at least one fin.

2. A sailing yacht according to claim 1, in which each fin has an aerofoil cross-sectional shape.

3. A sailing yacht according to claim 1 or claim 2, in which on each side of the keel, one fin is incorporated in the plane of which is at an angle to a plane perpendicular to the keel of between 0 and 45", the fin extending in a downward direction.

4. A sailing yacht according to claim 3, characterised in that said angle is 20 .

5. A sailing yacht according to any preceding claim, in which the foot of each fin has a width which is more than 30% of the width of the tip of the keel.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Sailing yacht The present invention relates to a sailing yacht with, as usual, a keel below the hull. Such a keel has the function to improve the stability of the yacht and its windward sailing performance by producing hydrodynamic side force opposing the side force on the sails, thereby preventing the yacht from making leeway. The present invention aims to further improve the side force and lift characteristics of the keel. This is obtained in that the keel in the vicinity of the tip on each side of the keel is provided with at least one fin. From tests it appeared that in this way substantial improvement in side force and lift characteristics can be obtained. The invention will be described with reference to the schematic drawings, in which: Figure 1 shows a side view of a part of the hull, the keel and a fin; Figure 2 shows a bottom view of the same; and Figure 3 shows a rear view of the same as a somewhat greater scale. The hull 1 of the yacht is as usual provided with a keel 2 and a rudder 3. The waterline is indicated with 4. The fins are indicated with 5 and can be incorporated in any keel but preferably to one having an inverse taper i.e. the length of the keel increases in a downward direction. The fins have an aerofoil or stream-lined cross-sectional shape. The present invention comprises two fins 5 incorporated in a keel 2 one fin being positioned on each side of the tip of the keel 2 at an angle of between 0 and 45" to the perpendicular plane of the keel 2 in a downward direction. The incorporation of the fins 5 improves the side force or lift production of the keel. The physical mechanism responsible for the generation of lift is that of vortex shedding. On three-dimensional bodies vorticity is shed wherever the boundary layer separates from the body. Hulltype bodies are generally designed so as to avoid any vortex shedding i.e. boundary layer separation at all. As a result, such bodies produce very little lift or side force of their own. A keel fitted to a hull produces a greater amount of lift or side force. If the fins are incorporated in a keel a far greater amount of lift or side force is generated. During movement of the yacht through the water the tip vortex of the keel is moved away by the fins from the plane of the keel, thereby reducing the downwash caused by the keel and hence increasing the left and,or decreasing the vortex drag of the keel. Because the reduction in downwash is the greater near the tip of the keel, the fins are most effective near that region. Another advantage of a keel which incorporates fins is that the span or draught of the keel increases with the angle of heel. Preferably the foot of each fin 5 has a width which is more than 30% of the width of the tip of the keel. By applying fins it is further possible to lower the centre of gravity of the ballast-weight which means an increasement of the stability. CLAIMS

1. A sailing yacht having a keel below its hull in which the keel, in the vicinity of the tip, and on each side of the keel, is provided with at least one fin.

2. A sailing yacht according to claim 1, in which each fin has an aerofoil cross-sectional shape.

3. A sailing yacht according to claim 1 or claim 2, in which on each side of the keel, one fin is incorporated in the plane of which is at an angle to a plane perpendicular to the keel of between 0 and 45", the fin extending in a downward direction.

4. A sailing yacht according to claim 3, characterised in that said angle is 20 .

5. A sailing yacht according to any preceding claim, in which the foot of each fin has a width which is more than 30% of the width of the tip of the keel.