GB2322334A

GB2322334A - Twin yacht keels

Info

Publication number: GB2322334A
Application number: GB9703900A
Authority: GB
Inventors: Stephen James Bryant
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-02-25
Filing date: 1997-02-25
Publication date: 1998-08-26
Also published as: GB9703900D0

Abstract

A yacht has twin keels A,B each independently pivotable about a horizontal axis extending fore and aft between a generally vertical and a generally horizontal position. The twin keels, which are attached to the hull of the yacht below the waterline, may be pivotable about a common horizontal axis or alternatively about two separate axes either side of and generally parallel to the fore and aft centreline of the yacht. Each keel, which contains internal ballast or has a ballast bulb, is aerofoil shaped, with a flat surface facing outboard and a curved surface facing inboard. The keels may be made from a slightly flexible resilient material such as a carbon fibre composite laminate.

Description

TWIN YACHT KEELS.

This invention relates to the keels of sailing yachts.

Yachts have keels to provide resistance to leeway and the keel often contains ballast to aid stability. Yachts often heel over to uncomfortable angles whilst sailing in strong winds. It is desirable to keep leeway as small as possible. It is more efficient and comfortable to sail upright.

The aim of this invention is to design keels for yachts which provide significant improvements to previous designs with regard to keeping leeway to a minimum, increasing stability, and sailing in a more upright attitude.

Provision is also made for reducing the draft of the vessel, combined with the ability to sit firmly on the ground when the tide is out, or stored ashore.

Accordingly this invention proposes: Two lateral ballasted keels pivoted on a horizontal axis extending fore a aft, which may be swung between a generally vertical and a generally horizontal position independently. The axis of rotation of the keels is below the waterline, and the keels are intended to remain at all times below waterline.

Alternatively the keels could be swung on two separate axes, either side of, and generally parallel to the fore and aft centerline of the yacht.

The invention is presented and further explained in the description of an example shown in the accompanying drawings in which: FIGURE 1 Shows a yacht fitted with the keels floating at rest.

FIGURE 2 Shows a yacht firmly sitting on the ground with the keels splayed.

FIGURE 3 Shows a yacht sailing to windward or beam on with the windward keel raised, the leeward keel down.

FIGURE 4 Shows a yacht running downwind with both keels raised equaly.

FIGURE 5 Shows the cross section profile of the keels FIGURE 6 Shows how the keels are tilted to a new angle of attack for running downwind.

FIGURE 7 Shows the toed in winglets at the tip of the keel.

Referring to figures 1, 2, 3, and 4 it will be seen that the two swinging keels A and B are attached to the hull of the yacht under the waterline in such a way that they pivot independently on fore and aft axes of rotation parallel with the centerline of the yacht.

Each keel can be swung between an almost horizontal position, to an almost vertical position.

Each keel contains internal ballast, or a ballast bulb attached to the outside edge. The control system is not shown. Each keel is aerofoil shaped, with the flat surface facing outboard, the curved surface inboard. (See figure 5). In figure 2 the yacht can be seen sitting on the ground with the tide out (or stored on the shore). The two keels are splayed out to the maximum (almost horizontal) The yacht sits firmly on the keels and the rudder(s).

In figure 3 the yacht is shown going to windward ur with the wind on the beam. The windward keel A is raised towards the horizontal enough to balance the force of the wind acting on the yacht's sails. The yacht remains more upright because firstly the center of gravity of the yacht is moved outboard to windward, and secondly because the hydrodynamic effort of the almost horizontal keel A is pushing downwards in the known manner, the faster the yacht goes, the greater the push.

This combination of features enables the yacht to sail upright, and carry more sail, and hence go faster.

The leeward keel B resist leeway because of it's shape in the known manner.

In figure 4 the yacht is shown running downwind with both keels almost horizontal. It would not be desirable to have hydrodynamic forces pushing the keels downwards in this circumstance, as it would cause deeper imersion of the hull, and slower speed. To improve this situation the axes of the two swining keels are lowered at the aft ends, adjusting the angle of attack of the two swinging keels. Instead of producing downwards thrust they now produce upwards lift. (See figure 6). Hydrodynamic forces decrease the wetted surface, and increase speed. As an added refinement the keels could be engineered from a slightly flexible resilient material (such as carbon fibre composite laminate) to absorb stresses.

It is possible to fit small fixed winglets C to the tips of the keels (see figure 7). These serve to reduce tip vortex losses in the known manner, but are also toed in towards the centreline of the yacht (when the keel is almost horizontal) , in order to compensate for the off centre drag of the horizontal keel, in much the same manner as a sidecar attached to a motorcycle is toed in.

The raising and lowering of the keel could be controlled manually by crew, and be accomplished by mechanical, hydraulic of pneunamitc means.

It is conceivable that the keels could be operated automatically in the same manner as an autopilot steers a boat. In this case an electronic clinomenter, suitably damped, would provide information to an electronic processor, which would then actuate the appropriate keel to compensate heeling of the yacht.

Claims

1. Two lateral ballasted keels pivoted on a horizontal axis extending fore and aft which may be swung between a generally vertical and a generally horizontal position independently. The axis of rotation of the keels is below the waterline, and the keels are intended to remain below the water.

2. Two lateral ballasted keels as claimed in claim 1 where the keels are swung on separate axes, either side of, and generally parallel to the fore and aft centerline of the yacht.

3. Two lateral ballasted keels as claimed in claims or 2 where the keels are aerofoil shaped, with the flat side always facing outboard and the cambered side inboard when the keels are hanging vertically.

4. Two lateral ballasted keels as claimed in claim 3 where the axes of rotation can be lowered downwards at the aft ends.

5. Two lateral ballasted keels as claimed in claims 1, 2, 3 and 4 constructed from a slightly flexible, resilient, material.

6. Two lateral ballasted keels as claimed in any preceeding claim operated manually by mechanical, hydraulic, or pneumatic means.

7. Two lateral ballasted keels as claimed in any preceeding claim where in a suitable control system operates the keels automatically.

8. Two lateral keels substantially as herein described with reference to figures 1 to 7 of the accompaning drawings.