Abstract:
A sail track and sleeve assembly is provided to rotate about a round mast so as to provide an improved airflow to the leeward face of the sail. A teardrop shaped boom having an open interior is rotatable about the mast and freely rotates with the rotating sail track.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention concerns a design of a mast and boom for a sailboat where the boom is self-supporting and self-vanging and the sail is fastened to a round mast by a sleeve and track assembly that rotates about the mast.  
           [0002]    In the past sails have been fastened to the mast by either by a series of hoops as seen in U.S. Pat. No. 2,378,877, or in a groove in the mast as seen in U.S. Pat. No. 5,787,830, or a track and slider mounted on a face of the mast. In these configurations the mast in front of the sail causes turbulence or a back eddy over the leeward face of the sail. This turbulence can be extensive particularly on a reach and reduces the power of the sail. One of the prior art solutions is to use a wing spar that rotates. This is difficult and expensive to build and cannot be de-powered at rest (i.e. the boat will sail at anchor). It has also been customary to use conventional booms that are essentially straight tubes that run substantially parallel to the waterline of a boat and employ a topping lift or hydraulic vang to hold the boom in position. In the prior art there are also complete sailing rigs rotating about a step as in U.S. Pat. No. 3,968,765. In addition there is the “Aero Rig” by Carbospars wherein an unstayed mast and integral boom rotate in deck bearings and keel bearings.  
           [0003]    One of the dilemmas facing all modern sloop rigs is that to make the jib effect to windward there must be a backstay to tighten the jib stay. Usually the tensioned backstay is fastened at the stern that creates great loads on the hull. This arrangement prevents the use of a full roach, full length battened mainsail. One solution is to use running backstays.  
         SUMMARY OF THE INVENTION  
         [0004]    The principal object of this invention is to improve upon aerodynamic performance of a sailboat.  
           [0005]    Another object of the invention is to provide a lightweight boom structure and sail slide track that rotates about a round mast.  
           [0006]    The solution obtained is close to ideal as the turbulence is virtually eliminated at all angles of sail trim. The construction consists of a round mast and a sail attachment device comprising a plurality of cylinders surrounding the mast together with a sail track coextensive with the mast and fastened to the cylinders. Ideally a boom structure is provided that is made integral with the cylinder and sail track to rotate therewith. The boom structure serves as an attachment point for twin backstays that provide the rearward support for the jib stay. This arrangement allows the use of a full roach, fully battened sail plan. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a side elevational view of a sailboat with the rig of the invention;  
         [0008]    [0008]FIG. 2 is a more detailed partial perspective view of the tripod boom and sliders;  
         [0009]    [0009]FIG. 2A is a partial perspective of the forward portion of the boom of one version;  
         [0010]    [0010]FIG. 3 is a more detailed rear perspective view of the basic tripod boom and sliders;  
         [0011]    [0011]FIG. 4 is a basic boom structure with the sliders in accordance with the invention;  
         [0012]    [0012]FIG. 5 is a cross section of the sliders and cylinder taken on line  5 - 5  of FIG. 3;  
         [0013]    [0013]FIG. 5A is a similar cross section of a grooved track embodiment;  
         [0014]    [0014]FIG. 5B is a partial elevational view showing the mast, hoop and slider; and  
         [0015]    [0015]FIG. 6 is a side elevation view on a reduced scale illustrating a sail stowed in the boom of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    In recent yachts it is customary to use a teardrop shape for the mast. Unfortunately this shape becomes very inefficient when the wind is on the beam. The mast then becomes a spoiler actively interrupting the vital airflow to the first third of the mainsail. To reduce the turbulence at all angles of sailing a round mast is used as it creates only slightly more turbulence to windward and off wind it has considerably less turbulence that a tear drop shape. Referring first to FIG. 1 there is illustrated a sailboat  10  having a fixed cylindrical or round spar  12 . Ideally, the sail track should rotate with the sail. To achieve this a plurality of hoops or sleeves  40  surround the mast  12  at spaced intervals. On the inner surface of the sleeves or hoops antifriction means will be provided such as a fluorocarbon plastic (polytetrafluorochloroethylene for example). Fastened to and extending between the hoops is a sail track  42  illustrated as a “T” shape in cross section onto which conventional sail sliders  44  may be engaged. The luff of a sail  46  is fastened to the sliders such as illustrated in FIG. 5A. As seen in FIG. 5B, the track element  42   a  may be a groove into which a boltrope luff may readily slide. The track elements are preferably formed by extrusion or machining while the sliders are generally machined castings. The mainsail  46 , in either case, will be supported in a vertical position by a conventional halyard (not shown). The tack is fastened near the base of the mast and the clew to the end of the boom as at  36 . Since the mast is fixed, the structure allows the track to rotate as a unit about the mast as the trim of the sail is altered.  
         [0017]    In FIG. 1 the sailboat is fitted with a jib  50  that essentially forms a balanced rig. However the invention will work equally well with a catboat rig as seen in FIG. 4 where the teardrop framework  16 ,  17  of the boom extends only from the mast and is fastened to sleeves or hoops  20   a  and  24   a.  The sleeve  24  will rest on bearings (not shown) to absorb the axial forces. Regardless of the physical arrangement of the boom, the use of a round spar or mast is essential to the invention as it created little turbulence to windward and off the wind. The use of the rotating sail track achieves a clean airflow.  
         [0018]    As best seen in FIG. 2, there is provided a tripod boom generally indicated at  14  having a “tear drop” frame with side elements  16 ,  17 , and a transverse brace  18 ,  18 ′ that joins the side elements to a mast sleeve  20 . The sleeve  20  rotates freely about the mast  12 . Ideally the forward portion of the boom has a transverse frame element  19  that joins elements  16  and  17 . On element  19  is fitted a track  21  and a sliding car  21   a  onto which the jib stay  30  is fastened. Supporting the boom frame are a plurality of bracing members  22  that terminate in a base sleeve  24  that has bearings to absorb the axial loads. Shrouds or stays such as side stays  26 ,  26 ′ back stays  28 ,  28 ′ and a jib stay  30  may be provided and will permit the use of a full roach, fully battened sail. It should be noted that the backstays  28 ,  28 ′ are affixed to the boom  14  slightly aft of the mast and not to the hull as is customary. Indeed, this arrangement allows not only a tensioned jib stay  30 , but also will allow the leech of the sail to open up going off the wind. This is particularly helpful for a full-length battened sail. The generous width of the boom  14  structure permits this result. There is no necessity for running backstays that have to be carefully released and retensioned on each tack. The sail may be stowed in the boom as seen in FIG. 6. The boom is supported by the truss configuration affixed to the two sleeves  20 ,  24  in suitable bearings that permit the boom to rotate as needed for sail trim about the fixed mast. Ideally the elements  16 ,  17 ,  18 ,  19 ,  22  may be fabricated from carbon fiber or aluminum tubing.  
         [0019]    As illustrated in FIG. 2, the boom is arranged for a balanced rig, i.e. one with a mainsail and jib, and in some cases can be fitted with a bowsprit  32 . The retractable bowsprit provides an attachment for one corner of an off-wind sail that may conveniently be stowed in the forward portion of the boom frame. The version illustrated in FIG. 2 has a sliding car  21   a  that permits the tack of the jib to move to leeward. This is advantageous as there will be less backwind created on the mainsail.  
         [0020]    In FIG. 4, there is illustrated the tripod boom for an unbalanced rig as for a catboat. Like reference numerals in FIG. 4 have the suffix “a”. In this arrangement the nose of the teardrop shaped boom is affixed to the mast with a collar  20   a  and is further supported by element  22   a  affixed to a spaced collar  24   a.