Circular linked rotating foil assembly for vessels

A sailing craft has a circular linked rotating structure mounted on a vertical support or mast and within the circular structure are a plurality of parallel thin foils. The entire circular structure may be rotated in two axes to achieve directional control of the sailing craft as well as to adjust the angle of the foils to the wind.

BACKGROUND OF THE INVENTION 
This invention relates to a particular foil sail for vessels and more 
particularly to a rotating foil arrangement that employs a plurality of 
parallel elongated narrow vanes. In small sailing craft, and particularly 
in sailboards, as for example those illustrated in U.S. Pat. No. 
3,487,800, it is common to employ a single triangular cloth sail which can 
be carried freely at various angles to the wind as a result of a universal 
joint at the base of the mast. When angled to windward and back, this rig 
is capable of simultaneously creating forward and upward lift, and the 
successful combination of these two forces has improved upon the 
conventional rigs as evidenced by the fact that the sailboard rig now 
holds the monohull speed record of over 35 knots. Efforts have been made 
to improve the lift performance of sails by improving rigidity, 
smoothness, and using high aspect ratio for better results. Thin, rigid, 
single high aspect ratio air foils have not been too successful because 
the height necessary to achieve the required sail area makes these rigid 
foils very difficult to control. In addition, a single foil requires some 
stiffening agents such as a mast to supply enough rigidity for control. It 
has accordingly been difficult to improve upon the present sail 
arrangements of a mast with synthetic cloth, highly tensioned by battens 
and using a wishbone boom which creates in effect a sail that is a very 
taut membrane and which is quite efficient. 
SUMMARY OF THE INVENTION 
The instant invention is directed to a series of foils that are joined 
together at each end by a circular structure which in one embodiment is 
itself an airfoil, the entire structure being capable of providing upward 
and forward lift when correctly angled to the wind. Simply stated, foils 
in a horizontal attitude provide upward lift while foils in a vertical 
attitude provide forward and upward lift. The foils that are utilized have 
a high aspect ratio and are thin to give high aerodynamic efficiency. It 
is known, for example, that the efficiency of an airfoil is dependent upon 
its aspect ratio which can be defined by the formula s.sup.2 /a, where "s" 
is the length of the foil and "a" is its area. Also, it is known that with 
a higher aspect ratio, the greater the coefficient of lift. The entire rig 
utilizes the principle of keeping a low coefficient of drag by using long, 
narrow foils. The entire foil structure is designed to be rotated both 
angularly with respect to the center line of the sailing vessel, as well 
as rotationally to change the attitude of the foils with respect to the 
wind and to vary the lift characteristics. In this configuration, the 
multiple foils may be neutralized by swinging them into a horizontal mode 
where all the lift is upward, or angling them downward from the horizontal 
to acquire forward lift. Such an arangement enables an operator to 
effectively reduce sail area by progressively swinging the rig more into a 
horizontal mode which directly reduces the heeling moment and converts 
that force to a useful upward lift.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings, there is illustated in FIG. 1 a sail boat hull 
10 having a rudder 12 with tiller 14 and for lateral stability, a 
centerboard 16. The sailboat has the usual cockpit 18 and just forward of 
the cockpit and forward of the centerboard there is mounted an upright 
support 20 which might also be termed a "mast". The upright support is 
received in a socket 22 within the sailboat hull, the mast preferably 
passing through the deck and into a mast step (not shown). To provide 
rotational motion to the mast, there is illustrated a laterally extending 
handle 24 which may have suitable extensions such as 25 thereon. 
Alternately, mast rotation may be obtained at the base of the mast by 
affixing various mechanical means such as quadrants with cable control or 
other devices known to the skilled shipbuilder. 
Mounted at the upper end of the upright support or mast 20, is a shaft 30 
that passes through the mast, and on the end of shaft 30 there is fitted a 
circular air foil 32 having a wall with a flat inner surface 33 to which a 
diametral support plate 34 is secured, the plate serving as the rigid 
mounting point for the shaft 30. Mounted in spaced positions along the 
diametral support 34, are a plurality of airfoils 38 that extend in 
parallel relationship between the diametral support and the circular foil. 
Rotation of the circular air foil is provided by any suitable means, here 
illustrated as a sheave 40 mounted on the shaft 30 and a second sheave 42 
mounted near the base of the mast to provide not only rotational support 
by means of suitable cable such as 44, but also the lower sheave 42 is 
provided with a suitable braking system to maintain the rotational 
attitude of the circular foil. 
Referring now to FIG. 4, it can be seen in FIG. 4A that the foils are 
arranged horizontally and in this condition there will be no forward force 
created, merely an upward lift and the boat essentially can be maintained 
at a mooring or at anchor. In FIG. 4B, the foils are shown at a partial 
angle to the vertical to achieve a driving force forward in moderate air. 
To move up wind, references had to FIGS. 5A and 5B where the angle of the 
wind to the angle of the entire circular foil rig is illustrated for both 
starboard and port tack arrangements. The illustration in FIG. 4C shows 
the foils vertical which would be used when the wind is fairly light, it 
being understood that as the wind increases, the foils are rotated more to 
the horizontal to decrease the heeling moment and increase the upward 
lift. FIGS. 5C and 5D show the manner in which the foils will be oriented 
on a broad reach, the angle of the entire structure being made more 
oblique to the hull than when one is trying to tack up wind. 
Essentially the invention thus far described provides the neccessary sail 
area by stacking a number of smaller high aspect ratio foils within a 
circular structure or duct which is formed by virtue of the fact that the 
circular structure itself is a foil. In this way, the incoming wind is 
channeled productively and the duct or the circular structure provides the 
foils with a beneficial end plate effect that reduces tip turbulance and 
improves lift. Further, containing the foils within the circular duct 
creates a very rigid structure which enables all the parts to be thin and 
light, features which directly enhance the air-dynamic efficiency. 
Referring to FIGS. 6 and 7, there is illustrated a second form of circular 
duct which is composed of two circular rims 50, 51 which is advantageous 
if the rig is to be used on a sailboard 54. In this embodiment, the 
support 20' is freely rotatable in a socket 56 in the board 54 but in 
other respects is identical to the above described embodiment. The two 
rims 50, 51 are adequate for providing structural rigidity and have the 
advantage of greater lightness and ease of holding as seen in FIG. 7. The 
arrangement loses some of the aerodynamic efficiency of the solid band, 
yet still provides some end plate effect.