Abstract:
A recreational watercraft device consisting of a light hull in the shape of a sail board hull and on the bottom a strut hydrofoil assembly. The hydrofoil has a bilateral symmetric plan-form with a pivot connection at the center of the hydrofoil span. The pivot connection joins the hydrofoil to the strut. The strut has a streamline cross-section. The plane of symmetry of the strut is positioned in the plane of symmetry perpendicular to the span of the hydrofoil. In operation the rider stands on the hull and reciprocates the hydrofoil up and down via a strut having a T handle. The elements of the strut hydrofoil assembly comprise a foil, a pivot, a strut, a T handle, and extension.

Description:
“NON PROVISIONAL” APPLICATION  
       [0001]     This is a complete “Non-Provisional” patent application which is filed less than 12 months from the filing date of a “Provisional” application, Application No. 60/605,645 which was filed Aug. 30, 2004  
       BACKGROUND OF THE INVENTION  
       [0002]     Watercraft sports have become increasingly popular particularly in the areas of wind surfing, sculling and more recently sea kayaking. Wind Surfing requires good balance, upper body strength as well as appropriate wind conditions. In particular, wind surfing typically may require several sizes of sails as well as boards, each of which are costly and require ample storage and transport facilities. Sculling and sea kayaking involve operating from a seated position in watercraft having a narrow beam. Each require a good sense of balance and accordingly appeal to a limited clientele, specifically those having requisite physical skill and physical conditioning. Furthermore, an active person who engages in each of these related watercraft sports, would need a substantial array of equipment to participate, including multiple hulls, masts, oars, paddles, rigging and sails.  
         [0003]     Accordingly, it is desirable to provide for a new and improved Recreational Watercraft with Hydrofoil to provide for hand propulsion, which is simple to operate and overcomes at least some of the disadvantages of prior art.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention is a recreational watercraft comprising a lightweight slender hull driven by a strut hydrofoil assembly including a hydrofoil pivot mounted on a strut extending through a penetration in the hull. An operator of this recreational watercraft stands on the hull and, grasping a T handle, reciprocates the foil up and down below the hull by means of the strut. The operator ordinarily stands in a cockpit located in the central portion of the hull. A brace is fixed above and athwart the aft end of the cockpit to aid the balance of the operator. Except for certain special features hull shape can similar to some popular kayak designs.  
         [0000]     Foil Strut Assembly:  
         [0005]     In the present invention the foil strut assembly comprises a hydrofoil, a pivot, a strut, a T handle, and an extension to the T handle. The hydrofoil has a bilaterally symmetric plan-form. A pivot connection joins the foil to the strut. The axis of the pivot is parallel to the span of the foil and perpendicular to the long axis of the strut. The strut has a streamline cross-section. The long axis of the strut cross-section is perpendicular to the axis of the pivot.  
         [0006]     The pivot axis is positioned closer to the leading edge of the foil than is the center of hydrodynamic lift on the foil. In the case of a symmetrical uniform section foil, the lift center is approximately ¼ of the cord length from the leading edge. The preferred embodiments of the present invention include foils with span-wise taper with varying amounts of sweep. It is preferred that the pivot axis be more than 6% of the mean cord length forward of the lift center.  
         [0007]     The geometry of the strut foil pivot assembly is such that the cord plane of the foil is free to tilt upward or downward through limited angles. These angles are preferably in the range +/−15° to +/−25°.  
         [0008]     Because the pivot axis is forward of the lift center, upward thrust of the strut on the foil tilts the leading edge of the foil upward in the direction of motion. Conversely, a downward thrust tilts the leading edge of the foil downward.  
         [0009]     A T handle is mounted at the upper end of the strut, and preferably includes a tubular extension. The extension telescopes with the strut and includes a locking feature so that the strut-extension assembly can be adjusted to various lengths.  
         [0000]     Hull  
         [0010]     The slender, lightweight hull includes a penetration or well located forward from the hull center. The well is located on the center plane roughly an arms length or about two feet forward of the normal standing position of the operator on the hull. The well is a tapered tube having an elliptical cross section. The small end of the tube intersects the bottom of the hull. The large end of the tube is directly above the bottom end and significantly above the waterline. The well tapers outward to a much broader elliptical opening at the upper end. The longer axis of the elliptical section are parallel to the long axis of the hull. The taper allows the strut to pitch fore and aft and side to side with respect to the hull.  
         [0011]     The hull has a skeg or fin at the stern. The skeg is preferably fixed to the stern as a separate fin, but may be molded into and blended with the aft end of the hull.  
         [0000]     Foil  
         [0012]     The hydrofoil shapes referred to in this discussion is not fundamentally different from airfoil lifting shapes used in aircraft. The customary term hydrofoil is used because the foil is immersed in water. The hydrofoils or foils of this discussion are shapes used to generate lift normal to the direction of motion through a fluid with minimum drag. They are similar to airfoil structures used in aircraft and to dagger-boards used in sailing craft. In the case of a dagger-board, a symmetrical cross-section is employed to provide lift normal to the cross-section with equal efficiency in either direction. In the case of an aircraft wing, the section is asymmetrical (cambered) with the mean-line of the cross-section concaved downward. This asymmetry provides the aircraft with a greater maximum upward lift before stall. In the case of the present invention, the up and down loads imposed on the foil are of similar magnitude, so a symmetrical section is appropriate. A wide range of published airfoil cross-sections may be chosen for use in the present invention, for example, “Theory of Airfoil Sections” by Abbot and Von Doenhoff. The present invention is not limited to a particular foil cross-section. However; the family of foil cross-sections more suited to the present invention will have symmetrical or nearly symmetrical cross sections with ratios of maximum thickness over cord length in the range 0.8 to 0.14, and with the maximum section thickness less than 40% of the cord length from the leading edge.  
         [0013]     The invention will be described for the purposes of illustration only in connection with certain embodiments; however, it is recognized that those persons skilled in the art may make various changes, modifications, improvements and additions on the illustrated embodiments all without departing from the spirit and scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a side view of the recreational watercraft of the present invention with the hull in partial longitudinal section and shown with a strut hydrofoil assembly extending through a well, and with the operator standing and operating the foil assembly.  
         [0015]      FIG. 2  is an oblique view of the strut hydrofoil assembly of the present invention of  FIG. 1 .  
         [0016]      FIG. 3  is an enlarged fragmentary sectional view of the strut hydrofoil assembly of  FIG. 1  showing the strut extending down through the well in the hull.  
         [0017]      FIG. 4  is a side view in section of the strut hydrofoil assembly with the foil leading edge angled downward, and showing forces acting on the hydrofoil during the down stroke.  
         [0018]      FIG. 5  is a side view of the strut hydrofoil assembly with the foil leading edge angled upward, and showing forces acting on the hydrofoil during the up stroke.  
         [0019]      FIG. 6  is a view from above of the recreational watercraft of  FIG. 1 .  
         [0020]      FIG. 7  is a transverse section view of the watercraft of  FIG. 6 , the section is just aft of the brace looking forward.  
         [0021]      FIG. 8  is a transverse section view of the watercraft of  FIG. 6 , the section is taken through the center of the well looking forward.  
         [0022]      FIG. 9  is a view from above of conventional sit-on kayak hull with the brace removed and with the operator seated and paddling as with a conventional kayak.  
         [0023]      FIG. 10  represents a center plane longitudinal section through the cockpit of a conventional sit-on kayak hull converted for use as part of the present invention by installation of the well, and the brace.  
         [0024]      FIG. 11  is a view from above of the T handle, and extension.  
         [0025]      FIG. 12  is a side view of the T handle, and extension.  
         [0026]      FIG. 13  is a front view of the T handle extension. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]     Referring to  FIGS. 1-8 , there is shown a recreational watercraft  10  comprising a lightweight slender hull  12  and a strut hydrofoil assembly  14  including a hydrofoil  16  pivotally connected to strut  17 . An operator  18  stands in cockpit  19  and reciprocates hydrofoil  16  up and down below hull  12  by means of strut  17  with a T handle  20 . Preferably, T handle  20  is about shoulder width.  
         [0028]     As is shown in  FIG. 1 , strut  17  extends through well  21  penetrating hull  12  near the forward end of cockpit  19 . Operator  18  ordinarily stands in  19  immediately forward of brace  22 . Brace  22  extends across the after end of cockpit  19  roughly 18″ above the bottom of said cockpit  19 . Operator  18  is greatly aided in maintaining balance by applying pressure against brace  22  with the back of the leg. Brace  22  is easily removed so the operator  18  can sit and paddle, as in a conventional kayak shown in  FIG. 9 . The brace  22  may have more than one mounting position to accommodate operators of different sizes.  
         [0029]     As is shown in  FIGS. 2-4 , hydrofoil assembly  14  comprises hydrofoil  16 , pivot  23 , strut  17 , T handle  20 , and handle extension  26 . Hydrofoil  16  has a bilaterally symmetric plan-form with a pivot connection  28  at the center of the span of hydrofoil  16 . The pivot connection  28  joins hydrofoil  16  to strut  17 . The plane of symmetry of strut  17  is positioned in the plane of symmetry perpendicular to the span of hydrofoil  16 . The strut  17  has a streamline cross-section. An opening on the bottom side of hydrofoil  16  below the pivot helps the pivot assembly clear its debris.  
         [0030]     As is shown in  FIG. 3 , pivot axis  23  of the foil strut connection  28  is parallel to the span of the hydrofoil  16 . The pivot axis  23  is positioned on or near cord line  29 , and closer to the leading edge of the hydrofoil  16  than the center of hydrodynamic lift  30  as shown in  FIG. 3 . In the case of a symmetrical section foil  16 , as shown in  FIG. 3 , lift center  30  is approximately ¼ of the cord length from the leading edge. Embodiments of the present invention may include hydrofoil span-wise taper with varying amounts of sweep. It is preferred that the pivot axis is more than 6% of the mean cord length forward of lift center  30 .  
         [0031]     In the above discussion the foil geometry shown in the figures was chosen in part for simplicity and ease of illustration. All cord lines fall in a common plane and the sweep of the leading edge  44  is such that the ¼ cord position of each cord line along the span is on the same straight line. Other hydrofoil geometries within the scope of this invention with different sweep angles will have lift centers at positions other than the ¼ cord position of the center section. Also, hydrofoils within the scope of the invention may have dihedral and angles, which elevate the hydrodynamic lift center of the hydrofoil to a point near and above the top of the cross section at the center span. In this last case the best position for the pivot axis moves toward the top of the section.  
         [0032]     Because pivot axis  23  is forward of lift center  30 , upward thrust of the strut  17  on the hydrofoil  16  tilts the hydrofoil  16  upward in the direction of motion. Conversely, a downward thrust tilts the hydrofoil  16  downward. See  FIGS. 4 and 5 .  
         [0033]     As is shown in  FIG. 2 , a T handle  20  is mounted at the upper end of the strut  17 . The T handle  20  preferably includes tubular extension  26 , which telescopes with strut  17 . Tubular extension  26  includes a locking means  31  so that strut  17  plus extension  26  can be adjusted to various lengths.  FIGS. 11, 12  &amp;  13  shows an embodiment of strut  17  plus extension  26  in three fragmentary views, top, side and front. Locking means  31  shown in  FIG. 111  is a threaded fastener which clamps a split lower position of extension  26  tightly onto an upper portion of strut  17 .  
         [0034]     As is shown in  FIG. 3 , pivot connection  28  of hydrofoil assembly  14  limits upward or downward tilt angles of foil  16  with respect to the strut axis. These angles are in the range +/−10 to +/−30°, defining zero angle as having the cord lines of the foil perpendicular to the long axis of  17 .  
         [0035]     As is shown in  FIG. 1 , hull  12  has a skeg  32  mounted on the stern portion of hull  12  as a separate unit. As an alternative embodiment, Skeg  32  may be molded in as an integral part of hull  12 .  
         [0036]     A preferred embodiment of cockpit  19  is shown in  FIG. 6  provides leg-room  33  for the operator to sit and paddle as with a kayak. Cockpit  19  of  FIGS. 1, 6 ,  7 , and  8  is similar to the cockpit of a sit-on type kayak. The sit-on kayak is characterized by a completely open cockpit with minimal volume, with the hull forming a water-tight shell. In  FIGS. 6, 7 , and  8  the cross hatched section areas  24  are water tight regions of the hull. The hull portion of the present invention may be constructed by modifying a kayak. In this case, well  21  and brace  22  are added to a conventional kayak hull.  
         [0037]      FIG. 6  shows cockpit  19  extends behind the normal center of buoyancy  34  and far enough forward from the center of buoyancy to provide leg-room  33  for a seated paddler. We define the normal center of buoyancy as the center of buoyancy under the combined weight of the hull plus operator  18  when the hull is trimmed properly in the water. The weight of the operator  18  is generally far greater than the weight of the hull. Therefore; operator  18  generally stands and maneuvers close to normal center of buoyancy  34 .  
         [0038]     The hull includes a removable brace  22  athwart the aft end of the cockpit close behind the normal center of buoyancy  34  and roughly 18″ above the bottom of the cockpit. The best standing position for the operator can be defined only approximately. The center of buoyancy is always located under the combined center of gravity of the hull and operator. The best position of operator  18 , standing or seated, is located to give the hull proper trim in the water. The weight of the operator will vary and the optimum trim for the hull cannot be defined precisely.  
         [0039]     Well  21  is located roughly 2 feet (about one arms length) forward from the normal standing position of operator  18 . Well  21  is a tapered tube having an elliptical cross section. The small end of the tube intersects the bottom of hull  12  on the hull centerline. The large end of the tube is directly above the bottom end, and is significantly above the waterline. Normally the top of  21  intersects the deck. However in some embodiments (See  FIG. 10 ) the top end of  21  does not intersect the deck because the deck may be absent at its location. Well  21  tapers outward to a much broader elliptical section opening at the upper end. The long axes of the elliptical sections are parallel the long axis of hull  12 . Use of the term elliptical here is descriptive, not mathematical, the cross sections of  21  may vary widely from a mathematical ellipse.  
         [0040]     Preferably, the taper of well  21  is at least +/−30° fore and aft, and at least +/−15° to the sides. The taper of  21  allows strut  17  to tilt forward, back and to the sides. Operator  18  is also able to rotate strut  17  on its axis through 360° by means of T handle  26 . The smaller end of  21  at the bottom of the hull is preferably just large enough to provide clearance on strut  17  when said strut is tilted to maximum angles.  
         [0041]      FIG. 9  shows a top view of the hull  12  with the operator seated and paddling. Brace  22 , and skeg  32 , and assembly  14  have been removed.  
         [0042]     The design of the hull, as is well known in the design of kayaks and other small watercraft, is always a trade-off between the need for stability and the desire for a low drag shape.  FIGS. 7 and 8  show sections through hull  12  of  FIG. 6 . These figures show a desirable feature combining low drag with needed stability. Lateral lobes or sponsons  41  extend hull  12  laterally above the waterline. Sponsons  41  provide what is normally termed secondary stability (righting moments that increase significantly when the hull tips to the side). The sponson  41  is a well known design feature that is especially advantageous to the present invention.  
         [0000]     Operating Configuration  
         [0043]      FIGS. 3, 4 , and  5  illustrate the operation of foil  16  when driven by strut  17 . In operation, strut  17  extends upward through well  21  to extension  26  of T handle  20 . Operator  18  stands aft of strut  17  and well  21 . In operation (see  FIG. 1 ), the operator  18  grasps the T handle  20 , and reciprocates foil strut assembly  14  forcefully up and down. Because pivot  23  is forward of the lift center  30 , leading edge  44  inclines downward when foil  16  is forced downward. As a result, the lift force on  16  has a forward component-driving watercraft  10  forward. Conversely, when the foil  16  is forced upward, leading edge  44  inclines upward. The lift force on the foil  16  again has a forward component driving watercraft  10  forward. The most comfortable efficient movement for operator  18  inclines the strut forward on the down stroke and backward on the upstroke. This inclination of the strut during the normal operating cycle adds to the inclination of the foil on both up and down strokes as illustrated in  FIGS. 4 and 5 . The taper well  21  permits the axis of the strut  17  to tilt substantially relative to hull  12 .  
         [0044]     This freedom of motion is important for the following reasons: 
        1. The comfortable natural reciprocation of  14  by operator  18  includes cyclic for and aft tilting motion of strut  17 .     2. A skilled operator will discover that controlled forward tilting of the strut  17  on the down stroke and backward tilting on the up stroke produces more effective propulsion, and that the motion of strut  17  relative to hull  12  is complicated by steering requirements and wind and sea conditions.     3. Hull  12  must be allowed to roll and pitch without forcing this motion on assembly  14 .     4. If there is a collision of foil  16  with bottom or with a submerged object, foil  16  can move rearward relative to  12  as the strut  17  tilts forward, allowing deceleration of  12  and operator  18  over a reasonable distance. 
 
 The combined length of strut  17  plus T handle  24  is adjusted to the preference and height of the operator. For example, a 6′ tall operator may comfortably reciprocate T handle  20  from 6.7° above deck level to less than 1.5° above deck. This 5.2° range of motion requires a water depth of more than 5.5°. The operator can accommodate shallower water depth by limiting the range of motion. This may be done more comfortably by grasping extension  26  below T handle  20 . The operator steers the watercraft by turning the T handle  20 , and can also reverse thrust and backup by rotating the T handle  24  through 180°. Turning said T handle provides a lateral thrust component for steering. Skeg  3  contributes to the steering moment by concentrating lateral resistance toward the stern. The lateral thrust of foil  16 , in addition to steering, generates an overturning moment, which is used as a source of dynamic stability by the skilled operator. The overturning moment is generated since the side thrust operates some distance below hull  12 . This moment tends to throw the inexperienced operator off the side. However; with experience, the operator exploits this moment to create dynamic stability. The skilled operator learns to instinctively use the lateral thrust of the foil for lateral stability. This instinct is similar to that employed when riding a bicycle. 
 
 Self Bailing Feature 
       
 
         [0049]     The aft end of cockpit  19  preferably has a sloping back wall as shown in  FIG. 1 . This surface aids the ejection of water from the cockpits when  10  is accelerated forward by a vigorous down stroke. Water will on occasion spill into the cockpit due to wave action or accidental tipping of the hull  12 . The cockpit ramps up to the rear deck, providing a fair flow path for water ejection from the cockpit to the rear deck.