WO1989003339A1

WO1989003339A1 - A sailing craft

Info

Publication number: WO1989003339A1
Application number: PCT/GB1988/000869
Authority: WO
Inventors: Norman Trevor Green
Original assignee: Norman Trevor Green
Priority date: 1987-10-17
Filing date: 1988-10-17
Publication date: 1989-04-20
Also published as: AU2605288A; GB8724379D0

Abstract

A sailing craft in which, in contrast to conventional craft, the normally fixed keel fin is provided with a variability of incidence capability to power the craft, in conjunction with the sail of the craft, through the water on a selected course. The provision of keel fin adjustability results in improved sailing efficiency and overall stability compared with conventional sailing.

Description

"A Sailing Craft"

FIELD OF THE INVENTION

The present invention relates to a sailing craft.

BACKGROUND OF THE INVENTION Sailing craft in use today employ sails to power their movement through water, such sails acting as aerofoils having a variable incidence capability of movement where incidence is taken to mean the angle between the chord of the aerofoil and the longitudinal axis of the hull or load carrying body of the craft.

By varying this angle of incidence, winds may be harnessed to power the craft on courses having varying angles to the wind direction.

In order to control the direction and movement of the craft, vertical hydrofoils in the form of fins projecting into the water from the hull of the craft in conjunction with the aerofoil are used. These consist of a variable incidence fin in the form of a rudder near the stern for steering and a fixed zero incidence hydrofoil further forward, which is used for resisting the lateral force on the hull produced by the setting of the sail in the wind.

The latter hydrofoil, usually called a keel fin

(to be distinguished from the keel of the craft upon which the actual framework is built) , centreboard or centreplate or, if mounted on the external sides of the hull, a leeboard, is necessary if the craft is not to have excessive leeway or lateral movement away from the wind. Without the keel fin, sailing would be possible but inefficiently so, because hull itself would constitute the sole reaction to lateral movement under the action of the sail.

Employing variability of sail incidence to power the craft means that the aerodynamic forces on the craft vary considerably in direction leading to disadvantages particularly in terms of reduced aerodynamical efficiency and control and handling of forward movement.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the disadvantages inherent in the design of conventional sailing craft by providing a sailing craft wherein a variability of incidence capability is given to the main hydrofoil namely the keel fin.

The invention is based on the realisation that it is immaterial in the interests of producing a resultant force as between the sail and keel fin to power the craft through the water, whether variable incidence is applied to the sail or the keel fin, or indeed a mixture of both.

Not only does this lead to simpler control mechanisms but, more- importantly, it enables the forces on sail and keel fin to be arranged such that the stability of the sailing craft under the action of wind and water forces is increased, compared with a fixed keel fin and variable incidence sail design and the efficiency of harnessing the energy of the wind to provide selected directional movement of the craft is improved.

The present invention also has an important effect upon hull design. Thus to ensure that the major part of the hydrodynamic reactive force is provided by the movable keel fin, the shape of the hull will preferably be designed with a shallow draft. In actual practice many existing hulls have shallow draft and will therefore lend themselves to conversion to a movable keel fin sailing alternative.

According to the invention there is provided a sailing craft comprising a hull, a sail mounted above the hull for engaging the wind, and a keel fin mounted beneath the hull for engaging the water over which the craft is to sail, characterised in that said keel fin is adjustable for variable control of its angle of incidence with respect to the longitudinal axis of the hull thereby to set up a resultant force as between the opposing forces on said sail, and said keel fin respectively acting to power the craft on a selected course through the water.

With this arrangement it becomes possible to sail the craft solely by controlling the sailing incidence of the adjustable keel fin with reference to a selected allowable angle of incidence of the sail. This may be done by making the amount of sheet of a conventional sail invariant by clamping the sheet such that the sail is held at said fixed angle under the action of the resultant forward driving force produced by the interaction of the sail and variable incidence keel. Preferably the keel fin is rotatably mounted to the hull of the craft, and provided with a fin boom control- lable from the cockpit of the craft.

The invention will now be described in more detail by way of example with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of a sailing dinghy incorporating the invention;

Figure 2 is a plan view of the sailing dinghy of Figure 1;

Figure 3 is a detailed sectional view showing the rotatable fin and fin boom arrangement of the craft of Figure 1;

Figure 4 is a detailed plan view of the rotatable fin housing, fin boom and fin sheet of the sailing craft of Figure 1; and Figure 5 is an illustration of a craft employing the invention sailing close-hauled.

BEST MODES OF CARRYING OUT THE INVENTION The sailing craft, in the form of a small sailing dinghy, shown in Figures 1 to 4, comprises a sail 1 mounted above the hull 2 of the craft and a rotatable keel fin 3 projecting beneath the hull 2.

A rudder 4 is mounted at the stern of the hull 2. The tiller 5 of the rudder 4 is controlled from the cockpit

6 of the craft as shown more clearly in Figure 2.

The keel fin 3, see more particularly in Figure

3, is attached by fixing pins 7 to a rigid support post 8.

An upper section 9 of the post 8 extends through a fin support section 10 in which it is rotable, the fin support section 10 being held securely in a housing

11 provided in the hull 2. Washers 12 and 13 are located on the support post

8 at either end of the fin support section 10.

The upper section 9 includes a fin boom 14 for adjusting the keel fin 3 from the cockpit 5 of the dinghy. A split pin 15 passes through the post 8 above the fin support section 10 to retain the keel fin 3 in position in the housing 11.

The fin boom 14 is provided with a fin sheet 16 fixed to the boom 14 and passing around pulley blocks

17 fixed at opposite sides of the deck 18 of the craft. he sail 1, see Figure 1, is provided with a sail boom 19, and a kicking strap 20 between the boom 19 and the mast 21.

The sail 1 is secured in the embodiment shown, such that its angle of incidence with respect to the longitudinal axis XX of the hull 2 is invariant under sailing conditions.

The selected angle of incidence is preferably 40°. This is achieved by clamping the sail sheet 22 at a fixed length. The sail sheet 22 is movably attached at one end to the sail boom 19 and at the other end to the deck 18.

To enable the craft to tack, the fixed angle of incidence established using the fixed length of sail sheet 2 may be transferred to the other side of the axis XX, by means of the clamped end 23 sliding in a traveller 24 arranged across the stern of the craft.

With the arrangement as described above, employing the variable incidence keel fin 3 in the determination of the conditions for forward motion, the heeling force applied to the craft by the wind acting on the sail 1, is reduced compared with that encountered with conventional craft under equivalent conditions of sailing. The result is that the craft may be operated in a more stable manner with the mast and sail remaining in a more upright position.

The reduction in the heeling force which the present invention provides may be used to further advantage to increase the driving force by using a larger sail or a taller but narrower sail i.e. with increased aspect ratio. Although this will increase the heeling force this will be no greater than the heeling force applied to conventional craft under equivalent sailing conditions. In addition, the reduction in heeling force achievable by the invention may be used by the craft designer to reduce the beam. Because the angle of incidence of the sail may be fixed i.e. on one side or the other of the axis XX of the craft, the craft may be designed so that the driving force passes through the centre of lateral resistance of the variable incidence keel in. Thus no balancing force, with accompanying drag, is required from the rudder.

Moreover the aerodynamic design of the sail may be improved because there is no necessity to vary its incidence other than from side to side. For example the gap between the base of the sail and the deck of the hull of the craft, a source of aerodynamic drag and loss of driving force, may be filled with additional sail.

Finally because of the coincidence of centre of effort and centre of lateral resistance in all points of sailing, the handling characteristics are improved and gybing is easier and safer, not only for that reason but also because the sail must move through only about half the angle than when gybing in a conventionally equipped craft.

An illustration of a sailing craft employing the invention and sailing close hauled, that is as directly into the wind as possible, is shown in Figure 5.

Under these sailing conditions the angle of incidence A of the keel fin 3 is set at 30°, and the sail 1 is fixed at what conventionally would be the setting for the reach point of sailing, that is the angle of incidence of the sail C is 40° .

Under these sailing conditions it can be shown that the heeling force is considerably reduced compared to that encountered in conventional craft under equivalent sailing conditions, and considerably improved overall control of the craft is possible.

While the invention has been described with reference to a sailing dinghy it is to be understood that it is equally applicable to craft employing a combination of sails and fins, together with a combination of hulls.

Claims

1. A sailing craft comprising a hull, a sail mounted above the hull for engaging the wind, and a keel fin mounted beneath the hull for engaging the water, characterised in that said keel fin is adjustable for variable control of its angle of incidence with respect to the longitudinal axis of the hull thereby to set up a resultant force as between the opposing forces due to wind and water on said sail, and said keel fin respectively acting to power the craft on a selected course through *^~h3 water.

2. A sailing craft as claimed in claim 1 wherein said keel fin is rotatably mounted to the hull of the craft.

3. A sailing craft as claimed in claim 2 wherein an upper support section for said keel fin is mounted in a housing provided in the hull, said keel fin being rotatable with respect to said upper support section.

4. A sailing craft as claimed in claim 3 wherein said keel fin is provided with a support pillar extending for rotatable movement through said upper support section to terminate in a fin boom operative from a cockpit of the craft

5. A sailing craft as claimed in any preceding claim wherein means are provided to restrain movement of the sail when engaging the wind from a predetermined angle of sailing incidence to either side of and with respect to said longitudinal axis.

6. A sailing craft as claimed in claim 5 wherein said retaining means comprises a fixable length of sail sheet.

7. A sailing craft as claimed in claims 5 or 6 wherein said predetermined angle of incidence is 40°.

8. A method of sailing using a sailing craft equipped with a sail for engaging the wind and a keel fin for engaging the water characterised by adjusting the sailing incidence of the keel fin to produce a resultant force as between the interaction of opposing forces on said keel fin and said sail to power the craft through the water.

9. A method as claimed in claim 8 wherein said sail is adjusted to a fixed angle of sailing incidence and the resultant force is provided by varying the incidence of said keel fin with respect to the sail.

10. A method as claimed in claim 9 wherein said fixed angle of incidence is 40°.

11. A sailing craft substantially as hereinbefore described with reference to and as illustrated in Figures

1 through 4 of the accompanying drawings.

12. A method of powering a sailing craft through the water substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.