Abstract:
A three-dimensional sail apparatus that is made up of a plurality of spacedly disposed foils and a sail cloth for attachment to the foils on opposite sides thereof. Each foil has opposed sail cloth supporting sides that together define a foil shape, A support is disposed between the sides for controlling the relative positioning between the sides of the foil, with each rail adapted to deflect under wind force against its related sail cloth so that the foil can assume opposite respective asymmetric foil shapes.

Description:
FIELD OF THE INVENTION 
   The present invention relates in general to a three-dimensional sail apparatus that employs airfoils for use on wind powered craft. More particularly, the present invention relates to an improved reversible airfoil that is used to support a sail fabric or sail cloth. 
   BACKGROUND OF THE INVENTION 
   In sailing terms the relative motion of a wind powered craft with regards to the wind direction may be referred to as sailing upwind, or sailing downwind. One sails downwind by positioning the sail to create as much drag as possible. This provides a wind pressure on the sail that pushes the craft along in the direction of the wind. For sailing downwind the sail configuration is not that critical. However, when sailing upwind or into the wind, the sail shape is more important. In order to sail upwind, the sails are positioned to generate aerodynamic lift in relation to the apparent wind. It is this lift that is translated into the driving force that propels the craft forward. When sailing upwind, drag is no longer beneficial, as it counteracts the resulting drive force. Therefore, it is important to developing sails that maximize lift while minimizing drag for sailing into the wind. 
   Three dimensional sails differ from conventional sails in that they have two surfaces of curvature rather than a single thin surface. These two surfaces create a pressure differential by forcing air to flow past them at different velocities, thus creating lift. As a result, high lift airfoils are asymmetrical and only generate lift efficiently in one direction. However, tacking in this manner is more difficult with a three dimensional sail due to its three dimensional fixed shape. 
   Accordingly, it is an object of the present invention to provide an improved three dimensional sail structure that is reversible as to its shape so as to facilitate lift in alternate directions. 
   Another object of the present invention is to provide a three dimensional sail apparatus that is reversible so as to assist in a “tacking” action. 
   SUMMARY OF THE INVENTION 
   To accomplish the foregoing and other objects, features and advantages of the present invention there is provided a three-dimensional sail apparatus that comprises a plurality of foils supported from a mast, a sail cloth for attachment to the foils on opposite sides thereof, and in which each of the foils includes a pair of rails that together form the foil shape, a plurality of spreaders that are spacedly disposed between the pair of rails, and a plurality of sliding connections that support the spreaders from the rails. The sliding connections enable the foil and attached sail cloth to reverse in direction from a first asymmetric shape to a reversed second complementary asymmetric shape. 
   Other aspects of the present invention include the sail cloth having spaced sleeves for attachment to each foil; an end one of the spreaders having a hole therein for receiving the mast; each spreader having opposite ends that are slideably supported from respective rails; each spreader having, in one embodiment thereof, a triangular shape and supported by one sliding connection to one of the rails and by two sliding connections to the other of the rails; each spreader including, in another embodiment thereof, a cross bar having a single attachment location to respective rails; each sliding connection includes a loop that connects from the spreader about the rail; the rail having a rectangular cross-section. 
   In accordance with another embodiment of the present invention there is provided a sail foil for supporting sail cloth and that comprises a pair of rails that together form the foil shape, a plurality of spreaders that are each disposed between the pair of rails with adjacent spreaders maintained in spaced relationship; and a plurality of sliding connections that support the spreaders from the rails with each spreader having at least one sliding connection coupled with each rail. The sliding connections enable the foil and attached sail cloth to reverse in direction from a first asymmetric shape to a reversed second complementary asymmetric shape. 
   Other aspects of the present invention include an end one of the spreaders having a hole therein for receiving the mast; each spreader having opposite ends that are slideably supported from respective rails; each spreader having a triangular shape and supported by one sliding connection to one of the rails and by two sliding connections to the other of the rails; each spreader including a cross bar having a single attachment location to respective rails; and each sliding connection including a loop that connects from the spreader about the rail. 
   In accordance with still another embodiment of the present invention there is provided a three-dimensional sail apparatus that is comprised of a plurality of spacedly disposed foils and a sail cloth for attachment to the foils on opposite sides thereof, with each foil having opposed sail cloth supporting sides that together define a foil shape, a support between the sides for controlling the relative positioning between the sides of the foil, and with each rail adapted to deflect under wind force against its related sail cloth so that the foil can assume opposite respective asymmetric foil shapes. 

   
     DESCRIPTION OF THE DRAWINGS 
     Numerous other objects, features and advantages of the present invention are described in conjunction with the accompanying drawings in which: 
       FIG. 1  is a schematic perspective view illustrating a sail apparatus embodying the principles of the present invention with multiple foils; 
       FIG. 2  is a perspective view of a single foil; 
       FIGS. 3-5  illustrate different positions of the foil of  FIG. 2  including a neutral position and respective alternating wind direction positions; 
       FIG. 6  is an enlarged fragmentary perspective view of the apparatus of  FIG. 2 ; 
       FIG. 7  is a cross-sectional view taken along line  7 - 7  of  FIG. 6 ; 
       FIG. 8  is a fragmentary perspective view of an alternate embodiment of the sail apparatus; 
       FIG. 9  is a fragmentary perspective view of the alternate embodiment of the sail apparatus also showing the attachment with the sail cloth; 
       FIG. 10  is a cross-sectional view taken along line  10 - 10  of  FIG. 9 . 
   

   DETAILED DESCRIPTION 
   This invention constitutes a reversible three dimensional foil or wing capable of automatically transforming its asymmetry from one contour to the opposite merely by adjusting its boat&#39;s direction with respect to the wind. By bringing a boat about, the wind automatically transforms the foil, thus becoming capable of developing driving forces on its new tack. Such action is accomplished via the inclusion of reversible foil or wing sections (foil  20 ), which transpose their asymmetry under a lateral force to change in a horizontal plane. Sections are described as follows: 
   The leading edge (end  25 ) of the section consists of a leading edge spreader profiled in perimeter to effect the leading edge of the section. Centered within the spreader is a hole to allow the spreader to slide up and down the mast or forestay for jib wings. Affixed by cantilever attachment are two flexible rails extending in the aft direction, which constitute section sides. Additional spreaders are included subsequently providing appropriate rail spacing at chord line positions. Such spreaders are attached to the rails by sliding connections. Two versions of spreaders aft of the leading edge spreader are contemplated. 
   1.) A flat triangle arrangement having two sliding rail attachments at two corners with the third corner being attached to the opposite rail in the same manner. 
   2.) The other comprises a pipe teed at both ends. It has a sliding attachment on each rail. 
   Encompassing these sections is sail material ( 12 ) having sleeves ( 15 ) on the inner side to support the sections and house the rails. Intermittent gaps along the sleeve provide access openings for attaching the spreaders and retaining proper chord line positioning of the spreaders. For foils or wings acting in the position of the main sail, the lower extent is fastened to a boom. The upper extent is fastened to a gaff. They can then be drawn into span (operating position) by hoisting them up the mast with the main haliard. Similarly, foils fabricated as working jibs may or may not require either a gaff or boom, and would be raised into span by hoisting them up with the jib haliard. 
   The foils or wings automatically reverse in contour by adjusting the boat&#39;s direction to the wind (changing tack). They may be lowered by releasing the haliard for stacking or storing on the boom or in the close proximity of the hull. Storage is conveniently achieved on board the boat. Such storage may be configured to pose no aerodynamic influence during periods of inoperation. Boat operation only requires steering the rudder and adjusting the sheet (line connecting boom or lower foil end) to the boat. Storage of the wing or foil may be accomplished on board the boat, thus eliminating any need for removal or storage elsewhere. 
   Reference is now made to the drawings and in particular  FIG. 1  which is a schematic perspective view of a sail apparatus that embodies the principles of the present invention. This apparatus  10  includes a sail cloth  12  supported about a plurality of foils  20 .  FIG. 1  also shows, primarily in dotted outline, the mast  14  of the vessel that uses the sail apparatus  10 . The three-dimensional sail apparatus of the present invention may be embodied in a number of different configurations corresponding to different types and constructions of sails. 
   The first embodiment of the foil structure is illustrated in  FIGS. 1-7 . Fragmentary views of a second embodiment are depicted in  FIGS. 8-10 . 
   In the first embodiment the three-dimensional sail apparatus foil  20  is comprised of elongated rails  24  that may be constructed of a lightweight wood or a lightweight metal material. These rails  24  terminate at respective ends at end members  25  and  26 . The end member  25  is provided with a hole  27  for engaging with the mast  14 . Each of the foils  20  is appropriately supported at space locations along the mast  14  such as schematically illustrated in  FIG. 1 . 
   The three-dimensional sail apparatus foil  20  also includes a plurality of spreaders  30  that in this embodiment are each of a triangular shape and extend between respective rails  24 . Each of the spreaders  30  is held between the respective rails  24  by means of loops  32 . The cross-sectional view of  FIG. 7  illustrates one of the loops  32  secured to a spreader  30  by means of fasteners  35 . In accordance with the present invention various types of fasteners may be used. Each of the loops  32  functions as a sliding member that enables limited sliding of the spreaders  30  along rails  24 . As illustrated in  FIG. 6 , the sail cloth  12  is preferably provided with tabs  15  between each spreader so as to limit the extent that the spreader can transition along the rails. Because each of the spreaders in this embodiment is illustrated as a triangular shape, there is one loop  32  on one side thereof and a pair of loops  32  on the opposite side thereof. These triangular members alternate in the manner illustrated in, for example,  FIG. 3 .  FIG. 7  shows each of the tabs  15  as stitched at  17  to the sail cloth  12 . 
   Reference is now made to  FIGS. 3-5  which may be considered as plan views of the foil  20  in the various positions. These positions are depicted with relationship to a center line  40 .  FIG. 3  depicts the foil  20  in what may be termed a neutral position. In that position it is noted that the center line  40  is basically a straight line extending between the end members  25  and  26 . The purpose of the illustrations in  FIGS. 3-5  is to indicate the manner in which the foil reverses depending upon the wind direction, from one asymmetric shape to a reversed asymmetric shape. 
     FIGS. 4 and 5  depict the manner in which the foil is deflected depending upon the wind direction. In  FIG. 4  the wind direction is indicated by the arrows  42  from above. Alternatively,  FIG. 5  depicts the opposite wind direction by the arrows  44  from below. It can be seen from the view of  FIG. 4  that with the wind direction indicated by the arrows  42 , that the top rail  24  becomes more linear or flattened and the bottom rail  24  becomes more bowed than that shown in  FIG. 3 . This causes the center line  40  to dip. Similarly, in the view of  FIG. 5  the bottom rail  24  becomes more linear or flattened and the top rail  24  becomes more bowed with the center line  40  being now arced upwardly. 
   Thus, the foil of the present invention has the ability to deflect in opposite directions depending upon the wind direction that the sail faces. There is actually a deformation of the foil between the possible positions shown in respective  FIGS. 4 and 5 . This greatly enhances the ability to be able to “tack” with the sail apparatus of the present invention. During the movement such as between the positions shown in  FIGS. 4 and 5 , it is noted that the spreaders  30  have the capability of moving slightly along the rail at the support loops  32  so as to readjust to the different positions illustrated. Again, as illustrated in  FIGS. 6 and 7 , the sail cloth  12  is attached by means of tabs  15  to the rails  24 . Of course, there is a sail cloth on either side of the rails  24 , only one of which is depicted in  FIG. 6 . With the use of these tabs, this assists in maintaining a space relationship between the spreaders while at the same time allowing some limited sliding of the spreaders as may be necessary in deflecting or deforming between positions. It is also to be noted that this action between these positions occurs virtually automatically depending upon the wind direction. The foil is not re-shaped manually but simply re-shapes itself, again depending upon the wind direction. 
   Reference is now made to a second embodiment of the present invention illustrated in  FIGS. 8-10 .  FIGS. 8 and 9  show only fragmentary portions of the foil, it being understood that a series of spreaders are used in a similar manner to that shown in  FIG. 2 . The embodiment shown in  FIGS. 8-10  includes rails  54 . Each of these rails may have a substantially rectangular cross-section and may be constructed of a lightweight plastic material. In the embodiment shown in  FIGS. 8-10  there is illustrated a series of spreaders  60 . Each of the spreaders  60  includes a rod-like member supporting at each end thereof a loop  62  that extends about each respective rail  54 . 
     FIG. 9  also illustrates the manner in which the sail cloth  12  is attached with its associated tabs  15  for somewhat controlling the movement of the spreaders  60  along the rails. Each of the loops  62  is sufficiently loose on the rails so as to permit at least limited sliding thereof along the rail. The cross-sectional view of  FIG. 10  illustrates further details of the spreader  60  with its end post  61  through which the loop  62  extends. The loop  62  may be secured in an appropriate manner within the end post  61  and is shown extending through the post  61  and about the rail  54 . 
   In this second embodiment each of the spreaders  60  may be of different lengths depending upon their closeness to the end members. The closer to the end members the shorter the spreaders may be. The number of spreaders used is usually a function of the length of the foil which can vary from vessel to vessel. The spreaders  60  are preferably constructed of a plastic material and the illustrated ones have a circular cross-section. In both embodiments described herein the spreaders are preferably somewhat loosely attached at the rails so that it is possible to provide the deformation, as illustrated in  FIGS. 3-5 . This free attachment is also characterized by the ability of the spreaders to have some limited linear movement relative to the supporting rails. 
   It will be understood that various modifications may be made to the embodiments disclosed herein. For example, it should be understood that a variety of materials may be utilized for both the rails and the spreaders. Also, other forms and shapes of spreaders may be used between the rails. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications within the scope, spirit and intent of the invention.