Abstract:
A sailboat mast including a straight lower portion and an arcuate upper portion. The arcuate upper portion has an aerodynamically efficient cross section designed to reduce drag. At least the arcuate upper portion is free to rotate with respect to the boat&#39;s hull in order to position the mast in line with the airflow for windward sailing, perpendicular to the airflow for downwind sailing, and at other appropriate angles for other conditions. The arcuate upper portion of the mast facilitates storage of the mast along a curved gunwale. The mast preferably incorporates a curved mast extension allowing an increase in the sail area beyond what is possible for a one-piece mast that is storable within the length of a boat.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This is a non-provisional application claiming the benefit of an earlier-filed provisional application pursuant to 37 C.F.R. §1.53(c). The provisional application was assigned Ser. No. 60/853,053. It listed the same inventor and was filed on Oct. 19, 2006. 
     
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable. 
       MICROFICHE APPENDIX 
       [0003]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    This invention relates to the field of watercraft. More specifically, the invention comprises a curved mast assembly for a sailing vessel. 
         [0006]    2. Description of the Related Art 
         [0007]    Masts have been used on sailing vessels for many centuries. They typically have a straight central axis, though they often taper from the base to the tip.  FIG. 1  shows a prior art sailing boat  10  equipped with a conventional straight mast  14 . Straight mast  14  is placed within mast step  22 , thereby attaching it to hull  12 . 
         [0008]    Cables are typically used to reinforce the mast. These run between the top of the mast and various attachment points on the hull. These reinforcing cables are collectively referred to as the “standing rigging.” 
         [0009]    Other conventional components are shown in  FIG. 1  as well. Boom  16  is attached to the mast near its base. Main sail  18  bridges the space defined by the mast and the boom. Jib  20  is rigged forward of the mast. Many other well-known components are shown in  FIG. 1 . These include a tiller, several thwarts, a transom, and an adjustable main sheet. 
         [0010]    Those skilled in the art will realize that the craft shown in  FIG. 1  is fairly small. It is of a type well-suited to fishing, in that it has a significant amount of useable space. However, that space is encumbered by the presence of the mast, boom, sails, and associated rigging. In order to use the vessel for fishing, it is desirable to take down and stow these components. 
         [0011]      FIG. 2  shows the same boat after the sails, mast, and rigging have been taken down. Base  28  of mast  14  has been removed from mast step  22  and the mast laid down in the boat. Furled sails and associated rigging have been omitted for purposes of visual clarity. 
         [0012]    The reader will observe that the mast does not fit within the boat&#39;s curved gunwales  36 . If base  28  is placed in the vicinity of stern  62 , then tip  26  extends well out the sides of bow  24 . Of course, the mast could be placed along the boat&#39;s centerline, but this would make movement within the boat difficult. The prior art mast cannot be efficiently stored along the gunwale, since the protruding tip interferes with fishing activity. 
         [0013]    Aerodynamic drag is another issue with prior art masts. The mast of a moving sailboat must “slice” through the relative wind moving over the boat. The straight mast shown in  FIG. 1  is akin to the straight wing airfoils used on older aircraft. A “swept” airfoil will reduce the aerodynamic drag. Thus, a mast design which improves upon the drag created by a straight mast is desirable. 
         [0014]    The ability to vary the sail area over a broad range is likewise desirable. The main sail can be raised and lowered to present larger and smaller surface areas respectively. However, the upper limit of surface area is conventionally reached when the top of the main sail is raised to the top of the mast. For days having relatively light wind, it is desirable to further increase the sail area. This is ideally done via providing an extendable mast top. 
       BRIEF SUMMARY OF THE INVENTION 
       [0015]    The present invention comprises a sailboat mast having a pivoting lower section and a curved upper section. The curved upper section facilitates stowage of the mast along a curved gunwale in a boat. The curved upper section also reduces wind drag when compared to a conventional straight mast. The pivoting lower section allows the entire mast to rotate so that the plane in which the curve of the upper section lies can be approximately aligned with the air flow over the boat. 
         [0016]    The invention preferably includes an extendable upper mast. This feature allows the total mast height to be increased, thereby allowing a greater sail area under appropriate conditions. The extendable portion preferably includes a radius of curvature which is about the same as the curvature of the main mast, so that the extendable portion can be extended over a variable distance. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view, showing a prior art sailing vessel having a straight mast. 
           [0018]      FIG. 2  is a perspective view, showing the vessel of  FIG. 1  with its mast removed and stowed: 
           [0019]      FIG. 3  is a perspective view, showing a curved mast made according to the present invention. 
           [0020]      FIG. 4  is a perspective view, showing the vessel of  FIG. 3  with its mast removed and stowed. 
           [0021]      FIG. 5  is a perspective view, showing the rotation of the curved mast in order to accommodate varying relative wind direction. 
           [0022]      FIG. 6  is an elevation view, comparing a prior art mast to the present invention. 
           [0023]      FIG. 7  is an elevation view, showing the use of a constant-radius arc for the curved mast and an arcuate mast extender. 
           [0024]      FIG. 8  is an elevation view, showing the operation of the arcuate mast extender. 
           [0025]      FIG. 9  is a sectional view, showing internal details of the mast&#39;s construction. 
       
    
    
     REFERENCE NUMERALS IN THE DRAWINGS 
       [0026]      
         [0000]    
       
         
               
               
               
               
             
           
               
                   
               
             
             
               
                 10 
                 boat 
                 12 
                 hull 
               
               
                 14 
                 straight mast 
                 16 
                 boom 
               
               
                 18 
                 main sail 
                 20 
                 jib 
               
               
                 22 
                 mast step 
                 24 
                 bow 
               
               
                 26 
                 tip 
                 28 
                 base 
               
               
                 30 
                 curved mast 
                 32 
                 pivoting base 
               
               
                 34 
                 arcuate portion 
                 36 
                 curved gunwale 
               
               
                 38 
                 constant radius arc 
                 40 
                 mast extender 
               
               
                 42 
                 mast cross section 
                 44 
                 main halyard tunnel 
               
               
                 46 
                 jib halyard tunnel 
                 48 
                 mast half 
               
               
                 50 
                 split line 
                 52 
                 luff tube 
               
               
                 54 
                 reinforced fiber jacket 
                 56 
                 slug 
               
               
                 58 
                 web 
                 60 
                 luff channel 
               
               
                 62 
                 stern 
                 64 
                 web anchor 
               
               
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION OF THE INVENTION 
       [0027]      FIG. 3  shows a mast made according to the present invention. Curved mast  30  includes arcuate portion  34  joined to pivoting base  32 . Pivoting base  32  is pivotally attached to mast step  22  so that the mast can rotate with respect to the hull. The other components—such as the sails—are modified to conform to the mast&#39;s curvature. The reader will observe how the modified main sale has an arcuate leading edge, whereas prior art sails have a straight leading edge. 
         [0028]    As for the prior art, curved mast  30  is preferably removable so that it can be stored within the boat.  FIG. 4  shows the mast removed. The reader will observe how arcuate portion  34  lies along curved gunwale  36 . While the curved mast still consumes some volume within the boat, it does not protrude significantly beyond the boat. Thus, it does not interfere with fishing and other activities. 
         [0029]    Prior art masts do not typically rotate with respect to the hull. Instead, the boom and main sail pivot around the fixed mast. The pivot may actually be a pinned joint or—in more traditional designs—a pair of boom jaws may rotate around the cylindrical external surface of the mast. The curved mast used in the present invention, however, is preferably constructed so that it is free to rotate as a whole. 
         [0030]      FIG. 5  graphically illustrates the need for this feature. A sailboat underway encounters wind flowing from many different directions.  FIG. 5  shows a boat sailing on a “close reach.” Its course is about 40 degrees off sailing directly into the wind. The curved mast has rotated so that the plane in which arcuate portion  34  lies is approximately parallel to the wind direction. This rotation allows even tension on the mainsail. 
         [0031]    Returning briefly to  FIG. 3 , those skilled in the art will realize that if the curved mast is not allowed to rotate, the boom must rotate about the mast in order to set the main sail&#39;s angle of attack (as for the prior art). However, if the boom rotates without the mast rotating, even tension cannot be maintained on the main sail due to the mast&#39;s curvature. Thus, the curved mast is preferably designed to rotate in unison with the boom. This is a substantial departure from prior art designs, where the boom is generally free to rotate with respect to the mast. In the present invention, the boom end nearest the mast is preferably locked to the mast so that when the wind pressure rotates the sail and the attached boom, the boom will rotate the curved portion of the mast into a favorable orientation (so that the curve is “slicing” into the wind). 
         [0032]    It may be desirable in some instances to allow the boom to move with respect to the mast in the pitch axis. Thus, a pivoting joint may be provided which allows the boom to be adjusted in pitch with respect to the mast. It may also be desirable to provide a small angular offset between the boom and the plane in which the curvature of the mast lies. This is preferable because the boom will rarely be aligned perfectly with the wind direction. The boom will more likely be offset 15 to 20 degrees from the wind direction. Thus, a comparable 15 to 20 degree offset between the boom and the plane in which the curvature of the mast lies can be provided. This would allow the boom to assume the optimum orientation while the curvature of the mast is pointed directly into the wind. 
         [0033]    Of course, differing wind conditions may mean that a differing angular offset between the mast and the boom is preferable. The angular offset can be made adjustable by any mechanism which allows the angular offset to be set, and then locks the boom to the mast so that they rotate in unison. A simple rope and pulley with a locking mechanism on the rope can be used for this purpose. 
         [0034]    Those skilled in the art will realize that only the curved portion of the mast gains an advantage by being free to rotate. Returning to  FIG. 5 , the reader will appreciate that only arcuate portion  34  needs to rotate. However, if the straight lower portion of the mast rotates as well, it will not alter the performance of the device (since a rotating vertical cylinder presents the same external surface no matter what the degree of rotation). Thus, the rotational joint can be provided in many different locations. It can be as low as the coupling between the bottom of the straight lower portion and the boat. On the other hand, the rotational joint can be as high as the lower extreme of the mast&#39;s arcuate portion. 
         [0035]    The storage efficiency is one advantage of the curved design. Other advantages exist as well.  FIG. 6  is an elevation view showing a comparison of a prior art straight mast to curved mast  30 . The wind flow is indicated by the arrow (Those skilled in the art will realize that the flow shown corresponds to a vessel sailing on a “close reach”). It is intuitively obvious that curved mast  30  produces less overall drag than straight mast  14 . The curved mast acts like a bird&#39;s wing slicing through the air. It thereby reduces overall drag and increases the sail&#39;s efficiency. 
         [0036]    The embodiments illustrated in  FIGS. 3 through 5  show arcuate masts having a constant radius of curvature. In this disclosure, the word “arcuate” should be understood to encompass a variety of curved shapes. Other embodiments are possible in which the radius of curvature is not constant. These embodiments might use a parabolic arc, an elliptical arc, or other second or higher order functions. However, the use of a simple constant radius arcuate portion has advantages. 
         [0037]      FIGS. 7 and 8  show an embodiment of the curved mast in which the arcuate portion has a constant radius of curvature (designated as constant radius arc  38 ). A channel can be provided within the mast&#39;s aft portion. The sail can be attached using this channel, such as by sliding slugs attached to the sail&#39;s forward edge into the channel (typical in the prior art). These slugs allow the sail&#39;s leading portion to slide up and down with respect to the mast. The sail is typically pulled upward using a tensile line that passes over a pulley near the top of the mast and is then attached to the top of the sail—the tensile line being commonly known as a “halyard.” 
         [0038]    The channel can also be used to slidably attach a mast extension. In  FIG. 7 , mast extender  40  is slidably attached to curved mast  30 . The mast extender is preferably given the same radius of curvature as the mast itself. The top of the main sail is attached to the top of the mast extender. The mast extender is then hauled up the mast—typically using a halyard assembly in which the free end of the halyard is attached near the middle of the mast extender. The halyard preferably passes over a pulley located near the top of curved mast  30 . The other end of the halyard terminates down near the bottom of the mast, where it can be grasped and pulled by a sailor. When the sailor pulls downward on the halyard, the mast extender is advanced upward. 
         [0039]    In most embodiments the mast extender would be attached to the top of the main sail itself. It would remain in this position even when the sail is lowered. As an example, it would be possible to lower the mast extender halfway down the height of the curved mast and eventually all the way to the bottom of the curved mast. In a lowered position, the user could grasp and adjust the mast extender. 
         [0040]      FIG. 7  shows mast extender  40  just as its tip has started to extend beyond the tip of the mast.  FIG. 8  shows mast extender  40  after it has been fully extended. A stop locks it into position. The mast extender allows the mast to be shorter while still retaining the same sail area. A shorter mast is, of course, easier to stow. 
         [0041]    Many types of sliding joints can be used to connect the mast extender to the curved mast. One approach is to construct the mast extender as a curved tube which slides within a curved cylindrical luff channel in the trailing edge of the curved mast. One could also pass the curved tube through a series of C-shaped brackets on the mast&#39;s trailing edge. Many other possibilities exist. 
         [0042]    Having now received an explanation of the curved mast&#39;s general shape and operation, the reader may wish to know possible internal details of the mast&#39;s construction. The mast can actually be constructed using a variety of known techniques. Thus, the example given should be viewed as only one embodiment among many possibilities. 
         [0043]    The mounting base portion can be conventional (excepting the necessity of the pivot joint).  FIG. 9  shows a cross section through the arcuate portion. The mast preferably includes several internal cavities. It therefore makes sense to build the mast in two halves which are then bonded together.  FIG. 9  shows mast cross section  42  comprised of two mast halves  48  bonded together. Each mast half includes voids which join to form tubular cavities running from a point above the mast step at the beginning of the arcuate portion of the mast to the top of the mast. The example shown accommodates a rigging for a main sail and a jib. Jib halyard tunnel  46  allows the passage of the jib halyard while main halyard tunnel  44  allows the passage of the main halyard. 
         [0044]    Luff tube  52  preferably runs for most of the mast&#39;s height. Its aft portion is left open to form luff channel  60 . The lower portion of the luff tube is left open on the bottom so that slugs  56  can be placed in the tube and then advanced upward by placing tension on the halyard. A series of such slugs  56  are used to attach the sail to the mast. Each slug is preferably a hollow “C” shape as illustrated. A series of web anchors  64  are placed in the hollow lugs. Each web is joined to the sail cloth itself. The web anchor can be formed by a variety of means, such as melting a portion of the web so that it deforms and fills the hollow center of the slug. 
         [0045]    As explained previously, mast extender  40  is also slidably engaged with the luff tube. Additional slugs can be used to attach the mast extender. Since these must carry a significant load, they are typically made as a close sliding fit with the interior of the luff tube. 
         [0046]    The hollow tubes running within the mast may be reinforced, such as by adding a reinforced fiber jacket embedded into epoxy resin. Since the material surrounding the luff tube must withstand substantial mechanical forces, reinforced fiber jacket  54  is preferably provided around luff tube  52 . 
         [0047]    The internal tubes can be simple voids in the mast material itself. However, they may also include metal or plastic liners in order to reduce friction. Likewise, the construction of the mast components could be altered while still practicing the fundamental aspects of the proposed invention. Accordingly, the scope of the invention should be defined by the following claims rather than any particular embodiment disclosed.