Patent Publication Number: US-6213044-B1

Title: Water craft with adjustable fin

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to water craft, and more particularly to a water board craft having a fin that is adjustable to a plurality of angular positions with respect to the direction of travel of the water craft. This invention is particularly useful when applied to a surfboard or sailboard to allow the rider to adjust the performance of the board to adapt to changing surf conditions and to variations in the weight and skill level of the rider. 
     Water board craft are well known in the art, taking the form of surfboards, sailboards, boogie boards, and other similar water craft that are maneuvered by the shifting of the weight of the rider. Such water craft typically include a board, formed of a strong yet buoyant material or combination of materials, and one or more fins attached to the bottom of the board. The fins provide stability to the board as it moves through or is propelled through the water. It has been long recognized that an adjustably mounted fin may provide improved performance by allowing the rider to adapt the board to varying conditions. 
     U.S. Pat. No. 5,493,989 issued to Anderson on Feb. 27, 1986, teaches an adjustable fin box system wherein the fin may be adjusted in the vertical, horizontal and angular directions. However, the angular freedom of movement provided by the Anderson device is about a horizontal axis, providing adjustment of the fin angle along the longitudinal axis of the board. The device of Anderson provides no freedom of movement for the fin about a vertical axis to adjust the fin angle with respect to the direction of movement of the board through the water. 
     U.S. Pat. No. 4,854,904 issued to Wahl on Aug. 8, 1989, teaches a sailboard with an adjustable keel mechanism. The Wahl device is designed to allow the keel to pivot about a vertical axis during the use of the board in response to loads imposed against the keel by the water, thereby eliminating crabbing and improving the speed of the board. The Wahl device does not provide the desired security of position of a fin in a variety of predetermined angular position. 
     U.S. Pat. No. 5,567,190 issued to Oates on Oct. 22, 1996, teaches another fin box assembly for a surfboard that permits the fin to be adjusted within an elongated fin box attached to a board. While the Oates device does provide for adjustment of the fin about a vertical axis, the range of adjustment is limited by the width of the fin box. Furthermore, the security of the fin position depends upon a friction interference between parts. These features may limit the usefulness of the Oats device and reduce its dependability in real world conditions. 
     BRIEF SUMMARY OF THE INVENTION 
     Thus there is a particular need for a water board craft having a fin that can be securely adjusted to a wide variety of angular positions with respect to the direction of travel of the board through the water. The mechanism used to adjust the fin should be easy to manufacture, simple to operate, and able to resist the large forces imposed on the fin during the use of the board craft. 
     A water craft is described herein including: a board; a fin box attached to the board, the fin box comprising a recess having a circular cross-section in a plane perpendicular to an axis of rotation; a fin having a base with a circular cross-section inserted within the recess, the fin being rotatable within the recess about the axis of rotation; and a means for securing the fin at any of a plurality of angles of rotation about the axis of rotation. The means for securing the fin may be as simple as a set screw in contact with a groove in the base, or as robust as a plurality of splines and slots formed in the base and fin box respectively along with a pinned connection between the board and the base. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawings in which: 
     FIG. 1 is a bottom view of a water craft incorporating a plurality of adjustable fins. 
     FIG. 2A is a top view of a fin box. 
     FIG. 2B is a side view of the fin box of FIG.  2 A. 
     FIG. 2C is a bottom view of the fin box of FIG.  2 A. 
     FIG. 3A is a side view of a fin. 
     FIG. 3B is a top view of the fin of FIG.  3 A. 
     FIG. 4 is a side view of a second embodiment of a fin. 
     FIG. 5 is a top view of a second embodiment of a fin box having an associated pin and gear fastening mechanism. 
     FIG. 6 is a side view of the gear of FIG. 5 showing its operative relationship with a key. 
     FIG. 7 is a partial sectional view of a fin installed in a fin box. 
     FIG. 8 is a partial sectional view of a fin installed in a fin box and secured by a fastener. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates one embodiment of a water craft incorporating the present invention. Surfboard  10  is shown from a bottom view to review three adjustable fin assemblies  12  protruding from a bottom surface of board  14 . Each adjustable fin assembly  12  includes a fin box  16  attached to the board  14  and a fin  18  having a base  20 . The surfboard  10  moved through the water along its longitudinal axis L, and each fin assembly  12  is independently adjustable to vary the angle of attack of the respective fin  18  with respect to the longitudinal axis L, as illustrated by angles A and B. 
     FIGS. 2A,  2 B and  2 C are top, side and bottom views respectively of one embodiment of a fin box  24  as may be used as fin box  16  in FIG.  1 . Fin box  24  includes an upper flange  26  that is preferably installed to be flush with the bottom surface of board  14 . A tubular shaped side portion  28  and a generally flat bottom  30  define a recess  32  having a circular cross-section in a plane perpendicular to an axis of rotation R. Reinforcing ribs  34  are formed between the upper flange  26  and the side portion  28  in two locations, although it may be appreciated that any number of such reinforcing ribs  34  may be used. The fin box  24  may be formed of plastic, fiberglass, metal or other material selected for its formability, strength and cost, and may be formed as a single integral piece or as individual sections joined with an adhesive or other fastening technique as may be known in the art. The fin box  24  is installed into the board  14  and secured with adhesive or fasteners. In one embodiment, a cap (not shown) is attached to the top of upper flange  26  to cover recess  32  during the process of glassing the board  14 . In the glassing process, resin is spread over the surface of the board  14  and at least partially over the cap and proximate upper flange  26 . The resin is then allowed to cure and is subsequently sanded smooth. During the sanding step, the cap is sanded off, thereby exposing recess  32  and forming a smooth glassed surface along the top of the board  14  and the top surface of the upper flange  26 . 
     FIGS. 3A and 3B are side and top views respectively of a fin  36  as may be used as fin  18  in FIG.  1 . Fin  36  has a base  38  with a circular cross-section that is operable to be inserted into recess  32  of fin box  24 . The mating dimensions of the fin  36  and recess  32  may be controlled to assure a snug fit while allowing the rotation of fin  36  about the vertical axis of rotation R after the base  38  is installed into recess  32 . In one embodiment the mating dimensions may be held to provide a gap of only about 0.005-0.020 inch between the parts, thereby assuring that friction alone will secure the fin base  38  within the recess  32 . Preferably, some form of releasable fastener is used to secure the fin  36  at any of a plurality of angles of rotation about the axis of rotation R. FIGS. 2A and 3A illustrate one embodiment of such a means for securing the fin. One or more threaded holes  40  are formed in the reinforcing web  34  to open on the top of upper flange  26  and into recess  32 . A set screw  42  is disposed in each hole  40  in threaded engagement with the fin box  24  and, when fully inserted, extending into the recess  32  to be in contact with the base  38 . One or more grooves  44  may be formed in base  38  to provide better contact with the screw  42 . If additional security is needed for maintaining fin  36  in a predetermined angular position relative to the axis of rotation R, a plurality of slots  46  may be formed in fin box  24  for receiving a plurality of projections  48  extending from the circular cross-section of base  38 . This arrangement permits the fin base  38  to be inserted into the recess  32  at any one of a predetermined plurality of angles of rotation about the axis of rotation R by alignment of the projections  48  with predetermined respective ones of the slots  46 . The angular extent of the slots  46  around the perimeter of recess  32  can be varied depending upon the desired range of adjustment of fin  36 . 
     FIG. 4 illustrates a side view of another embodiment of a fin  50 . In this embodiment, a plurality of holes  52  are formed in base  54 . As can be seen by viewing FIGS. 4 and 5 together, these holes are operative to receive a pin  56  moveable attached to the board  14  and passing through a side portion  58  of fin box  60 . With pin  50  withdrawn from recess  62 , fin  50  may be inserted into recess  62  in any predetermined one of a plurality of angles about axis of rotation R so that pin  56  is in alignment with a corresponding one of holes  52 . Pin  56  is then inserted through the selected hole  52  into recess  58 , thereby providing preventing both vertical and rotational relative movement between fin  50  and fin base  60 . Pin  56  may be moved between the engaged and disengaged positions by any variety of mechanisms, for example, by the rotation of gear  64  interfacing with corresponding threads or teeth  66  formed on pin  56 . 
     FIG. 6 is a side view of gear  64  showing its mating relationship with a key  68  used to manually rotate gear  64 . Gear  64  has a shaft portion  70  rotatably affixed to board  14 , and threads or teeth  72  for mating with corresponding threads or teeth  66  on pin  56 . A shank portion  74  is formed to mate with a correspondingly shaped recess  76  formed in key  68 . The use of a key  68  allows the top of gear  64  to be maintained flush with or below the surface of board  14 , thereby ensuring the safety of the rider and a clean aerodynamic shape for the board surface. It may be appreciated that other means for moving and securing the pin  56  may be used, such as a latch mechanism having a handle that lays flat with the surface of the board  14  when not in use. It may be further appreciated that in lieu of the use of holes  52  in fin  50 , pin  56  may be allowed to simply apply compressive force against base  54 , or to interface with a groove, such as groove  44 , formed in base  54 . Once in the engaged position, pin  56  may be restrained from movement simply by the friction fit between the pin and nearby structures, by a spring device (not shown) interfacing with the teeth  72 , 66 , or by a cap that snaps over shank portion  74  and fits securely into a recess in board  14 . 
     FIG. 7 illustrates a partial cross-sectional view of another embodiment of a water craft built in accordance with this invention. A fin  80  having a base  82  is secured into a fin box  84  glued or otherwise secured in a bottom portion of a board  78 . The fin base  82  may be splined with a plurality of projections  86  that interface with corresponding slots (not shown) formed in fin box  84 . Alternatively, the mating surfaces of the base  82  and fin box  84  may be smooth. Fin  80  may be inserted into fin box  84  at any of a predetermined angular positions about axis of rotation R. The interaction of the projections  86  and slots precludes angular movement of the fin  80  relative to the fin box  84 . Relative vertical movement of these parts along axis of rotation R is precluded by the insertion of retainer  88  into groove  90  formed by matching grooves  92 , 94  formed in fin base  82  and fin box  84  respectively. Retainer  88  is in threaded engagement with fin box  84  for insertion through passageway  96 . Once fin  80  is inserted into fin box  84 , retainer  88  is inserted into passageway  96  and tightened into position by mating threads  98 , 100 . Retainer  88  is formed of a flexible material, such as plastic or hard rubber, to allow it to be inserted along the curved path of groove  90 . In one embodiment, retainer  88  extends along about 30 degrees of the circumference of base  82 . The contact between retainer  88  and groove  92  restrains the relative movement of fin  80  and fin box  84  along axis of rotation R. If no projections and slots are provide on the mating surfaces of the base  82  and fin box  84 , the friction generated between the retainer  88  and the base  82  and fin box  84  may also serve to restrain relative motion between these parts around axis of rotation R. 
     FIG. 8 illustrates an embodiment similar to that of FIG. 7 except that fin  102  is secured vertically in fin box  104  by a fastener such as screw  106 . Fin  102  is formed to include a threaded opening  108  for engagement with respective threads  110  formed on screw  106 . Screw  106  also includes a head  112  that is in contact with the top surface of water board  114  within recess  116 . Screw  106  resists the vertical relative movement between the fin  102  and fin box  104 , and it may also provide all or a portion of the restraint against relative angular movement between these parts. 
     Fin boxes  24 , 60  define a recess  32 , 62  in the bottom surface of board  14 . Other embodiments of this invention may forgo the use of a separate fin box, but rather make use of a recess having a circular cross-section formed directly into board  14 . Such a recess may be formed by drilling a hole in the board  14  or by forming a side wall directly in the board shape during fabrication of the board  14 . If a set screw  42  or pin  56  is used as a fastener for such an embodiment, a hole would be formed directly into the board  14  and extending into the recess for passage of the screw or pin. 
     The adjustable fin of the present invention may be installed on an existing water craft as an upgrade. Existing fins may be removed, as appropriate, and an adjustable fin assembly  12  installed by known board repair/fabrication steps including drilling, gluing, and sanding. A kit for such an upgrade operation may include a fin box  24 , one or more screws  42 , and a fin  36 . Kits may be packaged for installing any of the described embodiments of the invention, including appropriate tools such as key  68  or an appropriate Allen wrench for moving the screw  42  from the engaged position to the disengaged position. 
     While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.