Ships – Sail or control means therefor – Specific sail structure or arrangement
Patent
1980-01-16
1982-08-17
Blix, Trygve M.
Ships
Sail or control means therefor
Specific sail structure or arrangement
114 39, B63H 904, B63B 1500
Patent
active
043443770
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a sail craft having a buoyancy body fastened to at least the upper portion of at least one of its sails.
BACKGROUND OF THE INVENTION
From U.S. Pat. No. 3,016,860 a sail boat is known, which has at the uppermost portion of the main sail an inflatable air bag which is inflated automatically like a balloon, when the boat capsizes. However, this air bag will produce a large air resistance when inflated and therefore cannot be used during normal sailing.
From Swiss patent specification No. 603 392 a windsurfer is known, by which the sail is provided with a buoyancy body consisting of a bag containing buoyancy material and being adapted to be folded around the uppermost portion of the mast and buttoned on to the sail, e.g. by means of press fasteners. A device of this kind cannot be used by sailing dinghies and keel boats, the sails of which are hoisted and lowered by means of a halyard. In addition, the mast, the buoyancy body and the sail form together a clumsy profile having a large "drag" and a small "lift".
SUMMARY OF THE INVENTION
It is the object of the invention to improve the buoyancy body in such way that it will permit hoisting and lowering of the sail in the usual way by means of a halyard, will produce an aerodynamically advantageous shape of the mast, the buoyancy body and the sail, taken in combination, and will also produce an "end plate effect", which will appreciably reduce the short circuit flow of air from the pressure side to the suction side of the sail across the upper portion of the sail, whereby, in addition, a much better aerodynamical efficiency of the main portion of the sail below the buoyancy body is obtained.
This is according to the invention obtained by the fact that the buoyancy body is made up of flexible foam material being attached to both sides of a single layer sail but having no connection with the mast, the foam material being shaped such as to form together with the sail and the mast an airfoil profile being as efficient as possible.
As the foam material has no connection whatsoever with the mast, but is attached to the sail only, it will be possible to hoist and lower the sail in the usual way by means of a halyard, and because the foam material is shaped in the said manner, the mast, the foam material and the sail will together form an effective airfoil profile having a rather large lift and a small drag. The front portion of the foam material will have a relatively large thickness, as its surface has to be flush with the surface of the mast in order to form the said airfoil profile, so that the foam material will have a comparatively broad, downward turned surface acting as an effective end plate at the upper portion of the sail. Thereby, the main portion of the sail below the foam material will acquire a greatly improved aerodynamical efficiency, because the ratio lift/drag will increase considerably on account of the end plate, as is known per se. These improvements in combination will result in an appreciable increase of the motive power produced by the sail. Measurements have indicated an increase of up to 85%.
At the same time the sail craft has been safeguarded against 180.degree.--capsizings by means of the buoyancy force acting on the buoyancy body, when this is partially submerged after a capsizing.
In order to obtain an advantageous thickness ratio of the airfoil profile (in the range from 6-12%), the buoyancy material may be shaped such as to fill up the two outwardly open spaces between the mast and the two sides of the sail and to stretch right from the mast to the aft edge of the sail.
A larger flexibility of the buoyancy body, so that this may be cambered by the force of the wind, can be obtained, if the foam material is made up of a number of thin, flexible plastic foam sheets being laid flat on top of each other.
In order to make a folding of the buoyancy body possible, when the sail is put into a sail bag, the buoyancy material may be split up into horisontal sections preferably extending right f
REFERENCES:
patent: 3016860 (1962-01-01), Johnson
patent: 3391668 (1968-07-01), Birchill
patent: 3395664 (1968-08-01), Greenberg et al.
patent: 4223621 (1980-09-01), Berger
Bartz C. T.
Blix Trygve M.
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