Patent Publication Number: US-2006016377-A1

Title: Sail corner attachment finishing system and method of attachment

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a new way to terminate sails at the corners (head, tack, and clew) or other termination points such as Cunninghams or reefs. This innovation replaces the current arrangement of stitched together reinforcing patches, webbing, and rings with a pre-formed composite structure. More specifically, the new system consists of a corner spar, enfolded within a layer of high tensile fibers, which in turn are laminated to the base sail. A flexible, self-adjusting, bridle engages the corner spar and serves as an attachment point for control lines, sheets, or halyards.  
     PRIOR ART  
      Today, a number of components must be sewn to the body of a sail in order to provide a proper anchorage for control lines, sheets, halyards and other attachments. The corners of the sail are of particular concern since these areas see the highest loads and contribute significantly to the overall shape of the sail in flight.  
      Current practice is to apply large cloth “patches” to help distribute the concentrated load at each corner, into the body of the sail. All fabrics have a tendency to stretch more along the bias then along the primary (warp) axis. Because of this, if a single piece of cloth were used for the patch, then the reinforcement would distort under load, upsetting the aerodynamics designed into the sail. In order to control problems of bias stretch, most patches are designed as multiple triangular gores, all with the lowest stretch axis, radiating outward from a common apex. This problem and others are discussed in Fracker U.S. Pat. No. 3,954,076.  
      In addition to patches, other layers of cloth, known as wadding, may be added. The wadding provides body and lateral stiffness to the sail. Without it, the sail would tend to fold and wrinkle from the point load at the corner. Finally, a piece of attachment hardware, such as a ring, must be secured to the sail using straps, webs, or ropes. All these individual pieces must then be sewn down to the base sail.  
      The use of fabric patches and wads was consistent with the materials and construction of traditional cloth sails. These sails required extensive use of cutting and sewing for their construction; the corner reinforcements were simply one more time consuming step in the process.  
      The advent of molded sails as described in Baudet U.S. Pat. No. 5,097,782 eliminated the fabrics, and the need to cut and sew large panels that were conventionally used in the body of the sail. Even though these molded sails are constructed as a monolithic composite membrane of films, polymers, and high tensile fibers, the corners were still constructed and finished using customary materials and techniques.  
     SUMMARY OF THE INVENTION  
      Instead of using layers of fabric plies to reinforce the corner of a sail, and instead of using a sewn and strapped on metal ring as an anchoring point, a composite assembly is used. The assembly consists of a corner relatively rigid member or spar held to the base or body of the sail by a net of high tensile fibers. These fibers wrap around the spar and are bonded to each side of the sail. A flexible bridle connects across or around the corner spar and provides a means to attach control lines, sheets or halyards to the sail.  
      This design solves a number of problems when compared to using a fixed ring. The assembly can be pre-manufactured, reducing or eliminating the extensive amount of hand labor currently needed to finish sails. It reduces the accuracy needed for placement since the bridle length can be adjusted.  
      The bridle can be made to be openable, eliminating the need for heavy shackles. The bridle can be somewhat flexible and also creates an inherent self-adjusting tension angle, desirable for proper sail trim. And finally, the bridle is easily replaceable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of an exemplary embodiment of the sail corner attachment of the present invention.  
       FIG. 2  is a plan view of a high tensile fiber web and carrier membrane shown in a flattened position.  
       FIG. 3  is an enlarged detailed perspective of the corner bar assembly from  FIG. 1 , without the fiber web, sail or sheets attached.  
       FIG. 4  is an alternate version of the corner bar assembled out of multiple pieces.  
       FIG. 5  is an alternate, monolithic, version of the corner bar, formed with an integral strain relief and a non-openable bridle.  
    
    
     DESCRIPTION OF THE INVENTION  
      All sails for sailing vessels, regardless of the method of making the sail (whether molded or made from panels), require finishing operations after the body of the sail is constructed. One of these operations is to provide some way of attaching lines or attachment hardware to the sail. Traditionally, this is done by sewing reinforcement patches into the corners of the sail, then attaching loops, rings, or other hardware through the use of straps and additional stitching.  
      The reinforcement is necessary since primary loads are transmitted through the corners into the body of the sail. The corners are of particular concern, since this is where the forces generated by wind and water are concentrated. More important the corners are the anchor points where those loads are transferred to halyards, sheets, shackles, or other control lines.  
      Customarily, various configurations of reinforcing panels have been employed to overcome the strains at the corners of a sail. Such thickening patches effectively add more plies of sailcloth, as the panel approaches the apex of the corner. To be effective, the weave of each patch must be properly oriented to avoid bias stretch and distortion, often requiring a patch to be made up of many triangular sections. By sewing the edges of the plies to each other, and to the sail panel, the corner is reinforced in increments intended to distribute the strain over a larger area of the sail.  
      The construction of such traditional patches and anchor points is extremely labor intensive. Additionally, even when a patch is made of multiple segments, current material limitations can only approximate ideal stress distributions.  
      This invention relates to hardware, finishing system, and method of uniformly reinforcing the corners of a sail. This invention also relates to the method of building such improved reinforcing attachments into the sails at a substantial saving of labor and material. This device is designed to replace the traditional system of cut and sewn cloth patches, wads, straps, and rings.  
      With this invention, a flexible composite structure is built up that more efficiently transfers loads from the body of the sail into an anchor point.  FIG. 1  shows this invention as attached to the body of a sail ( 1 ). An array of high tensile fibers ( 2 ) radiates from a corner spar assembly ( 3 ). The fibers are bonded to the body of the sail ( 1 ) along with a protective cover film ( 4 ). These fibers run from one side of the sail to the other and serve to retain the corner spar ( 3 ). A bridle ( 5 ) of rope or cable connects the corner spar ( 3 ) to a conventional control line, sheet, or halyard ( 6 ).  
      The spar bridle arrangement solves a number of design problems when compared to using the traditional closed ring. It reduces the accuracy required for corner placement since the length of the bridle can easily be changed. It provides a self-adjusting tension angle, and the bridle is easily replaceable. Additionally, the bridle can be made so that it can be opened or disconnected, allowing control lines or sheets to be attached without the use of heavy shackles.  
      Note that even though this invention was developed for use on boat sails, it could be equally well employed for other applications. Particularly in those cases where an anchor point must be attached to a flexible base. For example, tie downs for tarps or tents, awing reinforcements, connections to large fabric buildings and structures, etc.  
      The web is made by stretching individual fibers from one side of the sail, around the corner spar, then returning them to the opposite side of the sail. Adhesives are used to bond the fibers to each side of the sail and to the corner spar. For clarity,  FIG. 2  shows the pattern of high tensile fibers and cover carrier film, as they would look if spread open. In use, this web of yarns would be wrapped around the corner spar assembly and bonded to both sides of the base sail.  
      In practice, the entire network of fibers would likely be preformed upon a film or fabric substrate, and then used to attach the spar to the sail in a secondary operation, as shown in  FIG. 2 . By inverting construction of the web assembly (so that the substrate film is the outermost layer), the film could double as a shielding cover, to protect the filaments underneath. The use or omission of a substrate or cover film should not be construed as limiting in regards to this patent.  
      To expedite the construction process, more than one filament could be applied in a single pass. This would give the web the look of groups of parallel yarns, each group radiating outward from the apex of the corner. The overlapping fibers, closer to the corner, would serve to build up the thickness and provide some lateral support to the base sail. Conversely, as the yarns radiate outward, they will naturally thin out and transfer the loads into a large area of the base sail.  
      It should be noted that typically a small portion of the corner of the sail body is removed before the corner construction is applied. The corner spar is the only rigid, structural, element within the invention. Its purpose is to tie all the fibers together and thus collect the loads that each filament carries. This structural bar would then transfer that load to a bridle or some other connecting device.  
       FIG. 3  shows a concept of the corner bar assembly before being attached to the sail. This assembly consists of the main corner spar ( 7 ). A tapered, flexible, strain relief element ( 8 ) is bonded to the spar. The strain relief will help ease the transition of the fibers as they wrap around the spar and lead into the sail. The strain relief will also prevent excess flexure along the interface between the end of the sail and the spar.  
      To conserve weight, crucial in sailing applications, the bar would be a hollow tube with a teardrop cross-section. The teardrop shape would provide the largest radius for the fibers to be bent around, and still taper easily back to the narrow thickness of the sail. The hollow design would also provide a way to loop a connecting line, the bridle, through the spar. A generous radius would be provided on the inside of the tube to minimize chaffing on the bridle.  
      Where the sail contacts the length of the spar, a flexible strain relief is added. This strain relief is necessary to prevent excessive flexing between the sail and spar. Particularly in situations where the control lines are unloaded, and flogging of the sails occurs. If this side-to-side bending, along a concentrated line, were allowed to go unchecked, then the fibers would prematurely fail due to fatigue.  
      The strain relief continues the taper created by the teardrop shape and would allow the fibers to smoothly blend onto the surface of the sail. The strain relief and the corner spar could be interlocked with a keyway shaped profile. This would provide additional strength and control of the joint. The spar extends approximately to the central axis of the corner.  
      In its simplest form the bridle is a single loop of rope fed through the length of the spar and knotted together, and for permanent applications this may be adequate. However, in most sailing applications it is desirable to be able to open the loop so that the sails and control lines can be easily changed.  
      One easy way to accomplish this is to double over a sort length of line and knot the ends together. A ball ( 9 ) or disk with a hole through it could then be strung over this double line, the knot preventing it from sliding off the opposite end. In this manor a loop of rope can be produced with a knob or handle on one end. Not only is this design easy to build but also the overall length can be easily adjusted by repositioning the knot.  
      This doubled length of line would now be fed through the length of the spar, the ball preventing it from passing entirely through. The loop that is now naturally formed in the free end of rope, can be fed through an eye in the control line, and hooked over the ball. This has proven to be effective for small sails and light loads.  
      For larger sails and loads, the bridle needs to be more sophisticated. For this application, the bridle would be a continuous loop of line spliced end-to-end. A small cross bar would be lashed into one end of the loop. An annular groove in the center of the cross bar would prevent it from slipping sideways. In use, it would be fed through the spar and control line just as before, but now hooked over a cross bar rather than a ball.  
      In certain circumstances, there could be advantages to variations of this basic design. From a strength standpoint, forming the spar into a bow or even into a C shape might help reduce weight. A shape like this might then require the fibers to be arrayed into a purely radial pattern. Perhaps additional yarns would then be added to provide overlap and cross fiber bonding. Further fiber patterns could solve other problems.  
      For unique sizes, the spar could be a multiple piece construction.  FIG. 4  shows an alternate concept of the corner bar assembly. This assembly consists of a simple piece of tubing cut at an angle at both ends. End bushings are fitted into each end of the spar and allow the bridle to be threaded through, protected from sharp edges. A strain relief element is bonded to the tube. The bridle in this figure is the basic loop of rope knotted together at one end with the knot embedded into a small ball handle.  
      In application where extreme flogging is not present, the strain relief might be eliminated. In other cases, it could be possible to mold a strain-relieving feature directly into the spar. An example of this would be to simply taper the spar cross-section to a narrow enough point that the material would flex.  
      Rather than feeding the bridle through the spar, hooks or cleats could be formed on the end of the spar. A continuous loop bridle could then be spread from hook to hook.  
      Another option would be to build a mechanical clamp into the spar that would anchor one, or both, ends of the bridle line. This clamp could take the form of a hold down strap, a tapered collet, retaining screws, or other physical restraint. In low wear situations, the bridle could even be bonded to the spar.  
      The bridle need not even be rope. Where weight is not an issue, the bridle could be made of cable or chain. These materials would provide even more variety of ways to anchor the ends. Finally, if the application is such that the pull direction is consistent, a non-flexible bridle could be used. This would include using solid bars, connecting plates, formed rods, and the like.  
      Optional enhancements and features can also be added. Attachment points for leech and foot lines could be incorporated into the corner spar. The outer edges of the center base layer or corner anchor panel could be scalloped to ease transition from film to sail. A further loop could be spliced into the bridle if necessary for additional sail control. A double bridle and panel incorporating both tack and Cunningham attachments could be used. The finished corner could be encapsulated with an elastomeric material using injection molding or high pressure laminating processes.  
      Thus, the teachings disclosed herein should not be construed as being limited, except for the content of the accompanying claims.