Abstract:
A modified mast and keel system for a sailing vessel. The mast is gimbaled to the hull, so that it can move in a pitch roll. A downward extension of the mast pivotally connects to a winged keel. An aft strut also pivotally connects to the hull and pivotally connects to the winged keel. The hull, the mast extension, the winged keel, and the aft strut combine to form a traditional four bar linkage which is used to adjust the angle of attack of the winged keel with respect to the vessel. The winged keel moves with the mast in pitch and roll. It also includes a hydrofoil having an angle of attack which can be changeable in response to the pitching of the mast. This hydrofoil thereby generates downforce which counteracts the lifting forces created by the mast. It also creates lateral forces to counteract the sideslip of the vessel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of marine vessels. More specifically, the invention comprises a wind-powered vessel having a gimbaled mast and winged keel. 
     2. Description of the Related Art 
     Sail-powered surfboards, canoes, and similar watercraft have come into widespread use during recent years. Most of these devices employ a fairly rigid mast attached to a surfboard by a pivot joint. Some, however, employ a large “kite”-type sail in place of a fixed one. This kite type sail is attached to the end of a long tether and may be allowed to ascend many feet ahead of and above the vessel. FIG. 1 shows one example of such a sail, designated as sail  10 . FIG. 1 does not show a prior art device. In a prior art device, main sheet  14  would typically be attached to a harness worn by a person riding atop hull  18 . It would not be attached directly to the craft. 
     Those skilled in the art will know that sail  10  can be adjusted in elevation such that the angle between main sheet  14  and the vessel approaches and exceeds forty-five degrees. In such a case, main sheet  14  (which—being a rope—only transmits tensile force) can exert considerable lifting force on the vessel. The vessel is only maintained on the surface via the weight of itself and its rider. 
     Those skilled in the art will also know that sail  10  will be blown in the direction of wind travel. The rider may not wish to go in this direction. However, when attempting to steer the prior art “kite”-powered vessels off this course, the vessel tends to “skid” along the surface rather than maintaining the desired course. The experienced rider must “cut an edge” of the board into the water to provide a source of lateral resistance. 
     BRIEF SUMMARY OF THE PRESENT INVENTION 
     The present invention comprises a modified mast and keel system for a sailing vessel. The mast is gimbaled to the hull, so that it can move in pitch and roll. A downward extension of the mast pivotally connects to a winged keel. An aft strut also pivotally connects to the hull and pivotally connects to the winged keel. The hull, the mast extension, the winged keel, and the aft strut combine to form a traditional four bar linkage which can be used to adjust the angle of attack of the winged keel with respect to the vessel. The four bar linkage can be set so that the winged keel maintain a constant pitch with respect to the hull. It can also be set to vary the pitch of the winged keel as the mast pivots upward and downward. Thus, the amount of downward or upward force created by the winged keel can be varied. 
     As the mast rolls in one direction, the winged keel rolls in the same direction beneath the hull, in order to keep the downforce generated by the winged keel in axial alignment with the forces placed on the hull by the gimbaled mast. As the mast pitches in one direction, the winged keel pitches in the same direction, again to keep the downforce in axial alignment with the mast. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a perspective view, showing the present invention with a sail attached. 
     FIG. 2 is a perspective view, showing the present invention. 
     FIG. 3 is a hidden line view, showing the pitching characteristics of the winged keel. 
     FIG. 4 is a hidden line view, showing details of the pitch and roll gimbals. 
     FIG. 5 is a hidden line view, showing how the winged keel is attached to the hull. 
     FIG. 6 is an elevation view, showing the operation of the roll gimbal. 
     FIG. 7 is an elevation view, showing the operation of the roll gimbal. 
     FIG. 8 is a hidden line view, showing the operation of the pitch gimbal. 
     FIG. 9 is a hidden line view, showing the operation of the pitch gimbal. 
     FIG. 10 is a perspective view, showing the invention from underneath. 
     FIG. 11 is a perspective view, showing the invention from underneath. 
     FIG. 12 is a hidden line view, showing a version which maintains a fixed angle of attack on the winged keel. 
     FIG. 13 is a hidden line view, showing the operation of the pitch gimbal. 
     FIG. 14 is a hidden line view, showing the operation of the pitch gimbal. 
    
    
     REFERENCE NUMERALS IN THE DRAWINGS 
     
       
         
               
               
               
               
             
           
               
                   
               
             
             
               
                 10 
                 sail 
                 12 
                 leader 
               
               
                 14 
                 main sheet 
                 16 
                 mast 
               
               
                 18 
                 hull 
                 20 
                 sailboard 
               
               
                 22 
                 skeg 
                 24 
                 winged keel 
               
               
                 26 
                 hydrofoil 
                 28 
                 fore strut 
               
               
                 30 
                 aft strut 
                 32 
                 roll gimbal 
               
               
                 34 
                 fore bearing 
                 36 
                 aft bearing 
               
               
                 38 
                 mast foot 
                 40 
                 pitch gimbal 
               
               
                 42 
                 hull slot 
                 44 
                 fore slot 
               
               
                 46 
                 aft slot 
                 48 
                 aft strut gimbal 
               
               
                 50 
                 fore pivot 
                 52 
                 aft pivot 
               
               
                 54 
                 elevator 
               
               
                   
               
             
          
         
       
     
     DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a complete assembly denoted as sailboard  20 . Motive force is supplied by sail  10 , which is similar in operation to a kite. For the particular version shown, the large sail area is connected to four leaders  12  (Many other types are known in the art). The four leaders  12  are joined to a single main sheet  14 . The leaders and main sheet are typically made of flexible rope. Those skilled in the art will know that “kite”-type sails have numerous control features allowing a user to adjust their elevation, surface area facing the wind, and other features. These control features are well known in the art. As they are not significant to the present invention, they will not be illustrated nor described in detail. Throughout this disclosure, the reader should bear in mind that although a small vessel is used for purposes of illustration, the devices disclosed can be used on a vessel many times this size. 
     Main sheet  14  is attached to mast  16 . Mast  16  is attached to hull  18  via a pivot joint which allows it to roll and pitch with respect to hull  18 . Mast  16  is substantially rigid. Main sheet  14  transmits a tensile load to the upper extreme of mast  16 , which load is ultimately transmitted to hull  18 . 
     FIG. 2 is a closer view of hull  18 . Skeg  22  descends from the rear portion of hull  18 . It provides directional stability and can be made movable to assist in steering, like the rudder on a typical craft. Elevator  54  is preferably provided to add pitch stability. Mast  16  attaches to roll gimbal  32 . Winged keel  24  also attaches to roll gimbal  32 . The lower portion of winged keel  24  includes hydrofoil  26  (a “wing” shape), the purpose of which will be explained subsequently. 
     FIG. 3 shows the vessel with mast  16  pitched upward somewhat. Winged keel  24  has pivoted downward from hull  18 . This motion is caused by a pair of struts attaching winged keel  24  to roll gimbal  32 . Fore strut  28  is rigidly attached to mast  16 . It moves with the mast. The lower end of fore strut  28  is pivotally attached to winged keel  24  at fore pivot  50 . Aft strut  30  is pivotally attached to the aft end of winged keel  24  at aft pivot  52 . The upper end of aft strut  30  is pivotally attached to roll gimbal  32 . Those skilled in the art will realize that roll gimbal  32 , fore strut  28 , winged keel  24 , and aft strut  30  combine to form a classic four-bar linkage. 
     FIG. 4 shows these attachments in greater detail. Roll gimbal  32  is secured within fore bearing  34  and aft bearing  36 . These two bearings link roll gimbal  32  to hull  18  while still allowing it to freely roll with respect to hull  18 . Mast  16  is firmly attached within mast foot  38 . Mast foot  38  is pivotally attached to roll gimbal  32  by pitch gimbal  40 —which can be a bearing or simply a pin joint. Fore strut  28  descends from mast foot  38 . Mast  16 , mast foot  38 , and fore strut  28  are all locked together so that they move as one unit. The “jogged” shape shown is provided to allow component clearance when mast  16  pitches upward and downward. Fore slot  44  is provided in roll gimbal  32  to provide clearance for the components. 
     Roll gimbal  32  also includes aft slot  46 . This provides clearance for the upper end of aft strut  30 , which is pivotally attached to roll gimbal  32  via aft strut gimbal  48 . As explained previously, the lower ends of fore strut  28  and aft strut  30  are attached to winged keel  24 . 
     The reader can readily observe in this view the shape of hydrofoil  26 . Those skilled in the art will thus appreciate that the mechanisms described allow mast  16  to pitch upward and downward, and to roll side to side. Those skilled in the art will also realize that winged keel  24  will pitch and roll in response to the movements of mast  16 . 
     FIG. 5 shows the same area of the vessel from underneath. Hull slot  42  provides clearance for the two struts. It includes angled side walls to allow for the pitching and rolling motions of the two struts. 
     The operation of the invention will now be described in detail. FIG. 6 shows a view of the vessel from astern. Since mast  16  is free to move in pitch and roll, it can only transmit tensile forces to the hull (A small amount of yaw can be transmitted, but for “kite”-type sails, this is not significant). In the configuration shown, the sail is above and to the right of the vessel. It therefore tends to lift the hull and drag the hull to the right. The person controlling the vessel in this configuration is attempting to steer a course to the left of the wind&#39;s travel. The desire is to use winged keel  24  to counteract the lifting forces and the forces tending to drag the vessel off course. The reader will observe in the view that mast  16  has rolled 30 degrees in a clockwise direction (With respect to its “neutral” vertical position). The operation of roll gimbal  32  and the other devices descended has caused winged keel  24  to roll through 30 degrees as well. Winged keel  24  thereby tends to counteract the uplifting force and the force tending to drag the vessel to the right. The result is that the vessel is able to hold a steady course, with all the forces acting in axial alignment. 
     FIG. 7 shows a situation where the desired course is to the right of the wind&#39;s travel. The sail is now above the vessel and to the left. Mast  16  has rolled 30 degrees in a counterclockwise direction. Winged keel  24  has also rolled 30 degrees in a counterclockwise direction. The forces generated by winged keel  24  therefore tend to be aligned with the central axis of mast  16 . 
     The mechanisms disclosed perform a similar function with respect to pitch motions of mast  16 —but with one additional degree of freedom. FIG. 8 shows mast  16  pitched far downward. Fore strut  28  and aft strut  30  are rotated to a position which retracts winged keel  24  up against the bottom of hull  18 . The geometry of the four-bar linkage is defined so that the angle of attack of hydrofoil  26  is neutral at this point. In other words, hydrofoil  26  is not producing any downforce as the vessel moves through the water. The geometry in question is the position of the four pivot joints (pitch gimbal  40 , aft strut gimbal  48 , fore pivot  50 , and aft pivot  52 ) in order to define the length of each “link” in the four-bar. 
     In FIG. 9, mast  16  has pitched upward considerably. Fore strut  28  has pitched correspondingly downward, pulling winged keel  24  down and away from hull  18 . The reader will also observe that the operation of the four-bar linkage has caused hydrofoil  26  to pitch downward. It now has a negative angle of attack, meaning that hydrofoil  26  will produce substantial downforce as the vessel moves through the water. This downforce is needed to counteract the uplifting force generated by the sail&#39;s tension on mast  16 . Thus, by studying FIGS. 8 and 9, the reader will appreciate that as mast  16  pitches further upward, hydrofoil  26  is given a progressively more negative angle of attack. This, in turn, creates progressively more downforce. The result is that the uplifting forces tending to lift the vessel out of the water when the “kite”-type sail is in a relatively high position are counteracted. 
     FIG. 10 shows a perspective view of the vessel from underneath. The reader will observe how the orientation of winged keel  24  moves with mast  16 . Of course, these motions in the pitch and roll axes occur simultaneously. That is, winged keel  24  is moved to accommodate mast motions in both pitch and roll. FIG. 11 is another view of the vessel from underneath the water surface—this time with the vessel approaching the viewer. Mast  16  is pitched upward and rolled in a clockwise direction (from the perspective of a person on the boat—counterclockwise from the perspective of the viewer). The reader will observe that the winged keel has rolled correspondingly, and that hydrofoil  16  has been inclined downward to create more downforce. 
     Those skilled in the art will know that the four bar mechanism disclosed can be altered to create an infinite variety of pitch functions for the winged keel with respect to the hull. The alteration in pitch can be made much smaller than depicted in the views. The pitch function can even be reversed so that as the mast pitches upward the winged keel pitches upward. Another desired configuration would be to maintain a constant pitch on the winged keel with respect to the hull. FIG. 12 shows such a configuration. A “parallel” four bar is created by matching the distance between pitch gimbal  40  and aft strut gimbal  48  to the distance between fore pivot  50  and aft pivot  52 . Likewise, the length between the pivot joints on fore strut  28  and aft strut  30  are matched. 
     FIG. 13 shows this configuration when mast  16  is pitched downward. FIG. 14 shows the same configuration when mast  16  is pitched upward. The reader will observe that the angle of attack for hydrofoil  26  on winged keel  24  remains constant with respect to hull  18 . A constant pitch is maintained on the winged keel. Known mechanisms can be used to finely adjust the pitch of hydrofoil  26  with respect to winged keel  24 . A small negative angle of attack can be set to increase downforce. The parallel four bar then maintains this pitch irrespective of the position of mast  16 . The term “downforce” is understood to mean the a force generated by the hydrofoil. If the mast is rolled to one side, this force will obviously not act purely downward. 
     Although the preceding descriptions contain significant detail they should not be viewed as limiting the invention but rather as providing examples of the preferred embodiments of the invention. Many variations are possible. As one example, other types of “kite” sails can be substituted for the one shown. One other such type is disclosed in U.S. Pat. No. 4,610,212 to Petrovich (1986). The triangular sail shown in Petrovich could be attached to the end of mast  16  in the present invention, as could many other types. Accordingly, the scope of the invention should be determined by the following claims, rather than the examples given.