Sail craft

A device for increasing the motive force of a sail acting on a sail craft and at the same time decrease the risk of having the craft turned bottom up after a capsizing are obtained by fastening to the uppermost portion of the sail (3) a certain amount of flexible buoyancy foam (8) which is shaped such as to form together with the mast (1) and the sail (3) an efficient airfoil profile having a smooth contour. On account of its thickness, this airfoil profile will further counteract the short circuit flow of air from the pressure side to the suction side of the sail. The buoyancy foam (8) has at the same time a volume which is large enough to keep the sail (3) and the mast (1) floating at the water surface after a capsizing of the craft. In order to make the folding of the sail (3) easier prior to putting it into a sail bag, the buoyancy foam may be split up into a plurality of buoyancy zones separated by folding zones.

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 from the mast to the aft edge of the 
sail and being separated from each other by folding zones.

The sail 3 shown in FIG. 1 consists of a single layer and is in a 
conventional manner along the forward edge and lower edge provided with a 
rope which can be inserted into grooves in a mast 1 and a boom 2, 
respectively. The uppermost portion of the sail 3 is split up into two 
buoyancy zones 4 and 5 being separated by a narrow folding zone 6. 
As shown in FIG. 2, the foreleech 7 of the sail is received in a groove 
along the aft edge of the mast 1 which consists of a profile obtainable on 
the market. At both sides of the sail 3 is fastened buoyancy material 8 
consisting of for example flexible foam plastic which may be foamed up in 
a mold so that it shall not subsequently be cut to shape. A piece of sail 
cloth 9 is laid tightly around the foreleech 7, the two layers of the 
cloth being sewed together closely aft of the foreleech 7. To the rear of 
this seam, the two layers of sail cloth 9 extend along the outer surfaces 
of the buoyancy material 8 at both sides of the sail 3, and the two free 
edges of the sail cloth 9 are sewed on to the sail 3 by a seam 10 along 
the aft edge of the sail. However, the sail cloth 9 may be dispensed with, 
if the "skin side" of the buoyancy material 8 is faced outwardly and is in 
itself satisfactorily smooth and even. 
It will be seen that the buoyancy material 8 is shaped such as to form 
together with the mast 1 and the sail 3 an aerodynamically advantageous 
profile having a much better lift/drag ratio than the profiled formed by 
the mast 1 and the sail 3 in combination. The thickness ratio of the 
profile of section II--II is about 0,25, but further down the thickness 
ratio will be appreciably smaller. Furthermore, the buoyancy material 8 
has a volume which is large enough to keep the sail 3 and the mast 1 
afloat in the water surface after a capsizing of the sail craft on which 
the mast 1 and the sail 3 is mounted. 
Instead of foaming up the buoyancy material 8 in the top half a mould as 
shown in FIG. 2, it is possible to use a plurality of thin layers of 
material being laid flat on top of each other and cut to shape to produce 
the desired shape as shown in the bottom half of FIG. 2. 
It is further possible to attach additional buoyancy material along the 
whole length of the forward edge of the sail 3, stretching for example 
from the mast 1 to the chain-dotted line 11 in FIG. 1. In this way an 
appreciable decrease of the drag of the sail and a small increase of the 
lift is obtained. Taken in combination this gives rise to a considerably 
larger motive force acting on the sail craft. However, for reasons of 
safety there is no need for this buoyancy material, as the buoyancy zones 
4 and 5 are sufficient. 
If buoyancy material is placed along the whole length of the forward edge 
of the sail, the mast profile should be adapted hereto. The profile may 
for instance consist of the front portion of a NACA 0012 bounded at the 
rear by a plane surface at right angles to the axis of symmetri of the 
profile. Hereby a still larger motive force of the sail can be obtained 
than in the case of the profile shown in FIG. 2. 
The sail shown in FIGS. 1 and 2 can be used for any sail craft, i.e. also 
for keel boats, whereby the motive force per square meter of sail area 
will be increased by up to 85%, mainly due to the reduction of the short 
circuit flow of air from the pressure side to the suction side of the sail 
main portion situated below the thickened buoyancy zones 4 and 5.