Controllable Wing Sail

1. Field of the Invention

The present invention relates generally to improvements in sails and rigging for sailing boats, and more particularly to a new, fully controllable, wing-type sail.

2. Description of the Prior Art

Sails and rigging for small sailing boats in the prior art can be divided broadly into two types: the conventional sail that is carried in the plane of a vertical mast with the plane of the sail maintained approximately perpendicular to the surface of the water; and the kite-like sail that is carried with the plane of the sail at an acute angle with the surface of the water. My invention is concerned with improvements on this latter type sail.

The conventional sail is well suited to drive large displacement type boats at speeds below their hull speeds. However, the fundamental problem with the conventional sail is that the driving force of the wind on the vertical sail surface creates an overturning moment which tends to overturn the craft. To resist this moment, several methods are typically used. For example, a large weighted centerboard or heavy ballast in the hull, multiple hulls, and outrigger techniques may be used to provide a righting moment. All of these conventional approaches to stability create additional drag resulting in a reduction of speed of the boat. The overturning propensity of the conventional sail becomes a particularly serious problem when large sails are used on lightweight boats in an attempt to attain high speeds. However, attempts to increase the speed of the craft by increasing the sail area or using very tall high aspect ratio efficient sails have required additional means for counteracting the increased overturning moment, thereby creating additional drag. These constraints therefore limit the speed of conventional sailing boats.

It is clear that planing and other non-displacement hulls together with efficient high lift-to-drag ratio sails are needed if a boat is to attain speeds equal to or greater than the wind velocity. It has been recognized in the prior art that the kite-like sail has the potential to overcome the overturning problem associated with the conventional vertical-plane sail and to provide the needed high lift-to-drag ratio. This type of sail is flown or suspended from a mast or other structure on the craft with its plane maintained at an angle with the water surface. The force of the wind on the kite sail creates a lifting force in addition to a propulsive force. If applied correctly, the lifting force prevents an overturning moment thus eliminating the need for ballast, heavy keels, multiple or wide hulls and the like. A single lightweight hull is sufficient, and high speeds can be obtained.

The kite sails proposed in the prior art generally fall into two classifications. In some designs, solid wing-like structures having fixed cambers are used, and others use more conventional flexible but non-stretchable fabric surfaces cut in such a manner that the camber is created by wind pressure. The basic problem with the kite sail is that of controlling the sail to maintain it in those optimum spatial angles with respect to the relative wind that provide maximum propulsive efficiency. Prior art kite sails using flexible sails and minimal spars and solid members generally depend on the wind to maintain the camber and to hold the sail in the proper position. When the wind subsides, or is light or "flukey", such sails may fall into the water or assume undesirable attitudes. Rigid and/or rigid spar-supported wing sails do not depend upon the wind to maintain their shape; however, such sails often tend to be cumbersome and heavy, and are not easily controlled, lowered, or stowed.

An example of an early version of the non-vertical sail is taught by Ljungstrom, U.S. Pat. No. 612,209. Ljungstrom uses a heavy mast and frame structure to support fabric sails at an angle to the water surface to thereby reduce overturning moments. The adjustments and controls are limited to variants of swinging the sail in pendulum fashion from a yard fastened to the top of a vertical mast. One version requires outrigger pontoons which complicate control problems when changing course. A later U.S. patent to McIntyre et al, No. 1,670,936 shows other techniques to hold the plane of a sail at a desired orientation with respect to the boat. McIntyre proposes both fabric and solid type sails. One disadvantage with the McIntyre fabric sail is that wind pressure is necessary to put a camber into the sail because the sail must be used with the wind first on one side and then on the other. The aerodynamic efficiency of his fabric sail is significantly lowered when the sails are angled out to avoid overturning moments resulting in limiting of the speed potential of the system. His concept of a solid wing sail swung from one side of the boat over the top to the other when tacking partially solves some of these problems; however, methods for handling, stowing, and controlling the undesirable freedom of the sail to revolve about its support spar are not shown.

Rowland, U.S. Pat. No. 2,126,665 uses a sail rigidly supported by side booms in lieu of a mast. The booms are supported by a large turntable used to rotate the structure when it is desired to change the direction of the craft. The Rowland design controls the plane of the sail well but suffers from poor aerodynamic performance with its poor effective aspect ratio. The design lacks flexibility since the turntable and rotating apparatus must be built into the hull. It would not be practical to move the rigging from boat to boat.

It is apparent that the prior art attempts extending over 100 years to provide a practical kite-type sail have not been successful. Except for occasional experimental craft, present-day sailboats continue to use the conventional vertical sail, and the conclusion can be drawn that the full potential of the kite sail has not been realized by any of the known prior art configurations.

The present invention is a wing-like sail with a novel boom, mast, and control arrangement that overcomes the disadvantages of the known prior art kite and wing sail systems. My system not only orients the plane of the sail080000000000000000000000000000000000000000000000000000000000000000