Patent Publication Number: US-7591229-B2

Title: Forespar for a sailing vessel

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to mechanisms and structures employed in sailing yachts. More particularly, this invention relates to mechanisms and structures for attachment of a jib. 
   In conventional sailing vessels a forestay is employed for attachment of the jib. The forestay is typically attached at one end to the head or part way up the head of the mast and attached at an opposite end to a location proximate the bow of the vessel. 
   SUMMARY 
   Briefly stated, a spar, herein also called a forespar, for a sailing vessel comprises an elongated member having opposite first and second ends and defining a longitudinal axis of rotation. The elongated member has a longitudinal slot. The elongated member further has a longitudinally extending aerodynamic surface defined by a quasi-elliptical shape with identical starboard tack and port tack leading edges symmetric about a plane through the rotational axis and the slot. 
   A mechanism, which may be a spool and a line engaged with the spool for selectively producing a rotation of the spool, is employed to rotate the spar about the axis of rotation. The quasi-elliptical shape has a minor axis which intersects the plane. The elongated member may taper from the first end to the second end. 
   The elongated member may be manufactured from carbon fiber material. The elongated member has a surface portion opposite the slot which is substantially planar in one embodiment. In a second embodiment the elongated member has a second portion opposite the slot which is concave. 
   The spar projects upwardly at an oblique angle from a centerline of the deck. A jib is attached to the spar via one or more sliders disposed in the slot. 
   A wire or rod may be disposed along the axis of rotation for rotatably mounting the spar. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a representative illustration of a sailing vessel incorporating a forespar; 
       FIG. 2  is an enlarged fragmentary sectional view, partially in schematic, of the forespar and a mechanism for rotating the forespar; 
       FIG. 3  is an enlarged sectional view, partly in diagrammatic form, of the forespar and further illustrating the attachment to a jib, partially illustrated; 
       FIG. 4  is a schematic view, partly in broken lines, of the forespar in cross section relative to the vessel and the jib and further illustrating the positions of leading edge surfaces at different rotational positions of the forespar; and 
       FIGS. 5A ,  5 B and  5 C are schematic and diagrammatic views of the forespar in section illustrating various possible cross sectional shapes for the forespar and the attachment to a jib, partially illustrated. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to the drawings wherein like numerals represent like parts throughout the several figures, a forespar for a sailing vessel is generally designated by the numeral  10 . The forespar  10  comprises an elongated member which has a surface configuration adapted to improve the performance of sailing vessels by incorporating an airfoil technology to the structure which is provided for the attachment of the jib. 
   As further illustrated in  FIG. 1 , a representative sailing vessel  20  has a mast  22  which projects vertically along the centerline C between the bow  24  and the stern  26  of the vessel. The forespar  10  is preferably attached to the mast  22  by a swivel connector  30  and to a location proximate the bow by a second swivel connector  32 . Other connector hardware and mechanisms may also be suitable. The forespar is rotatable about a longitudinal axis which is oblique to the deck and mast. The forespar  10  can be designed to replace the conventional forestay to which the jib  40  is attached or can be mounted on the forestay. It should be appreciated that the forespar  10  need not be attached to the top of the mast  22 , but may be attached at various locations along the vertical extant of the mast. 
   The forespar  10  is preferably manufactured from carbon fiber, fiberglass or other suitable material. The forespar structure is best appreciated by reference to various representative cross sections as illustrated in  FIGS. 2 through 5 . The longitudinally extruding surface shapes  50  may be described as quasi-elliptical in cross-section and symmetric about the minor axis M. Opposed first and second surfaces  52  and  54  continuously taper to form identical leading edges  56  and  58 . The leading edges  56  and  58  of the forespar function in a manner analogous to the leading edge of an airfoil, such as NASA 4412 or similar airfoil configurations. The leading edge radius R ( FIG. 2 ) is preferably one to two percent of the chord of an airfoil, although a larger radius may also be used. For a chord length of 15 feet, at the foot of the jib the radius accordingly would range from 2-4 inches. 
   The forespar is provided with a longitudinal groove or slot  60  which retains the conventional slides  42  (only one illustrated) employed to attach a jib. The slot  60  is located at one end of the minor axis M of the ellipse so that the forespar is symmetrical about this location and will have the same surface shape for the leading edges  56  and  58  on the port tack and on the starboard tack. The port tack and starboard tack positions are respectively designated PT and ST in  FIG. 4 . 
   The cross section of the forespar  10  may be tapered from the root to the tip to conform to the change in chord of the jib.  40 . The forespar can retain the same shape as the size is tapered. Alternatively, the shape of the forespar may be changed as the forespar is tapered. However, the forespar must retain a cross sectional surface shape which is symmetrical about the minor axis M. 
     FIG. 5  shows several typical shapes  50 A,  50 B,  50 C which might be chosen to be compatible with different jib designs or to compensate for differences in the inflow air angles at different heights above the deck. With reference to  FIG. 5 , and as viewed along the longitudinal extent surfaces  54 A and  54 B respectively opposite surfaces  52 A and  52 B are substantially planar surfaces  54 C opposite surface  52 C is concave. The forespar cannot be twisted nor have a twisted structure from root to tip, since this would not maintain the required symmetry relative to the minor axis M. 
   With reference to  FIG. 4 , it should be noted that the forespar presents the same shaped leading edge contour on the port tack PT and the starboard tack ST. This is accomplished by making the aft surface contour of the spar a mirror image of the forward surface, and then reversing the forespar end as the vessel tacks so that the opposite end is presented to the wind. The mainsail, in coming about, forms a mirror image relative to the centerline C of the vessel. Thus, the jib and mainsail will have the same performance on either tack. 
   The forespar  10  presents a smooth aerodynamic surface at the top or suction side of the jib, but also presents a blunt end at the low or pressure side of the jib. This blunt end does not cause a significant loss in performance as the low pressure side has a negative pressure gradient and the flow will not separate or cause a stall. 
   The forespar  10  is designed to rotate about a fixed axis A as shown in  FIG. 2 . A rod or wire  34  may extend from the root to the tip, to provide an axle for rotation. Alternately, a suitable attachment fitting can also be provided at the ends of the basic mold of the forespar structure. Anti friction bearings (not illustrated) may be provided at the root tip of the forespar in a manner similar to the conventional roller furling rig. It is generally desirable to locate the axis of rotation A relatively close to the sail attaching slot  60  since this will reduce the torque transmitted to the forespar by the sail. 
   With reference to  FIGS. 1 and 2 , a spool  70  may be attached at the root of the forespar as illustrated. Control line  72  permits the vessel skipper to rotate the spool at any desired angle. 
   When the vessel tack comes about, the skipper must rotate the spar through an angle of approximately 220 degrees as illustrated in  FIG. 4 . This angle is adjustable to accommodate the wind and sea conditions. Such flexibility is useful to the racing skipper. 
   For smaller vessels the forespar  10  can be attached to a conventional rod or wire forestay. A simple drum lever (not illustrated) can be attached to base to accomplish the rotation. Since the forespar  10  is a rigid structure, it will not lose its shape as the jib luffs when coming about. The sail will luff later and fill sooner than with a conventional rig and the upwind performance will improve. 
   It is believed that the forespar  10 , as illustrated, will provide an increase of 10% or more in the force or lift generated by the jib and also a comparable increase in the efficiency or lift to drag ratio of the sail plane. Consequently, an increase in the speed of the boat and in the upward sailing angle would result.