Abstract:
A surfboard having composite covered honeycomb deck and bottom surfaces. The surfboard has a hollow inner volume which contains a longitudinally oriented stringer. The stringer is spaced both from the nose of the surfboard and from the tail of the surfboard so that the nose and tail are more flexible than the length containing the stringer. The process of making the board is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     The field of the invention is broadly sporting goods and more particularly to water borne sporting goods, such as surfboards, wind surfers, wake boards and sailboats. 
     Typically, surfboards are made utilizing a urethane foam core. The foam core is shaped to the desired shape. The core is then covered with a composite material which is cured, smoothed and polished. 
     Various alternative designs have been proposed and used. A recreational board having a honeycomb core is shown in U.S. Pat. No 5,514,017. The honeycomb core is surrounded by a fiberglass scrim and with a second laminating layer. 
     Another recreational board is shown in U.S. Pat. No. 5,266,249. This board is formed by placing honeycomb core laminates in a mold and placing a vacuum bag inside the hollow structure. The vacuum bag pulls the honeycomb core laminate against the mold while it is cured. The vacuum bag is then removed through a hole in the hollow member. The hollow member has an inner support wall, which also has a honeycomb core surrounded by composite material layers. 
     An expanded polystyrene filled board is commercially available under the trademark “Tuflites.” The expanded polystyrene blank of this board is formed in a mold. The blank is then surrounded by a sandwiched laminate containing a PVC sheet foam. 
     While the present invention is useful for a number of recreational boards, such as wind surfers and wake surfing boards, it is known to be more challenging to make a surfboard, since a surfboard must flex a desired amount and in desired locations. In the present foam shaping process, the foam core is shaped to create the desired flexibility. To date, no other board forming process has resulted in the desired flexibility present in conventionally shaped boards. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to make a hollow surfboard which will flex in an amount and at locations desired by surfers. 
     The present invention is for a surf board having a deck and a bottom. In one aspect, an embodiment has a deck fabricated from a laminate having an outer composite layer, an intermediate core fabricated from a honeycomb material, and an inner composite layer under the honeycomb material. The deck portion is joined to a bottom portion also fabricated from a laminate having an outer composite layer, a honeycomb inner core, and a bottom composite layer. A stringer comprising an elongated member is adhered to the inner surfaces of the deck and bottom. The core does not extend either to a nose or a tail of the surfboard so that the nose and tail are more flexible than that portion of the surfboard containing the elongated stringer. In another aspect, the stringer has a layer of urethane foam between its lower surface and the inner surface of the bottom to provide a degree of flexibility. Preferably, the stringer is about half the length of the surfboard and is positioned longitudinally and closer to the tail than to the nose. 
     The present invention also is for the process of forming the above-described surfboard. The process includes the steps of forming a first layer of honeycomb core into the shape of a deck of a surfboard. The core is covered top and bottom with resin and fiber, which extends past the outer peripheral edge of the honeycomb core. This deck laminate is placed on a shaped concave deck mold and surrounded with a vacuum bag. The vacuum bag pulls the laminate against the mold after which it is heated and the laminate cured. The bottom is formed utilizing the same steps. After curing, a stringer is adhered longitudinally to the inner surface of the deck or bottom. Next, an adhesive composition is placed on the exposed side of the stringer and the deck and bottom pieces are joined around the outer flaps thereof and cured to form the assembly into a hollow surfboard having a longitudinal stringer. Preferably, the adhesive composition which is placed on the stringer after it has been adhered to one of the surfaces, is a urethane prefoam which rises and forms a bond between the stringer and the inner surface of the board half to which it is adhered. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing the underside of the surfboard of the present invention. 
     FIG. 2 is cross-sectional view taken along line  2 — 2  of FIG.  1 . 
     FIG. 3 is an exploded perspective view thereof. 
     FIG. 4 is an enlarged cross-sectional view of a portion of the deck of the surfboard of FIG.  1 . 
     FIG. 5 is a cross-sectional view taken along line  5 — 5  of FIG.  1 . 
     FIG. 6 is a cross-sectional view analogous to FIG. 2, except showing a pair of stringers. 
     FIG. 7 is a cross-sectional end view of a deck and a bottom mold used in the process of the present invention. 
     FIG. 8 is a cross-sectional view analogous to FIG. 7 showing the deck and bottom pieces in a cured state in their respective mold halves. 
     FIG. 9 is a cross-sectional view of the mold halves of FIG. 8 in a closed configuration. 
     FIG. 10 is a cross-sectional view showing the inner surface of the bottom and the stringer. 
     FIG. 11 is a cross-sectional view of an alternate embodiment of the stringer of FIG.  10 . 
     FIG. 12 is a cross-sectional view of an alternate embodiment of the stringer of FIG.  10 . 
     FIG. 13 is a cross-sectional view of an alternate embodiment of a stringer of the surfboard of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A surfboard of the present invention is shown in perspective view in FIG.  1  and indicated generally by reference character  10 . Surfboard  10  has a bottom  11 , a deck  12 , and a fin  13 . The fin itself is conventional and typically more than one fin is used. 
     A stringer  14  is shown in phantom view in FIG.  1  and has a forward end  15  and a rear end  16 . Stringer  14  is shown in cross-sectional view in FIG.  2  and is of a C-shape having an upper surface  17  and a lower surface  18 . Upper surface  17  is glued to the deck undersurface. The lower surface  18  is adhered to the bottom inner surface, preferably through a layer of urethane foam  19 . 
     As shown in FIG. 3, the deck and bottom are formed separately after which the stringer is adhered to either the inner surface of the deck or the inner surface of the bottom. After the deck and bottom are joined, the other surface of the stringer is adhered to the other inner surface by the extension of a prefoam. 
     Deck  12  has an outer composite layer  19 ′ having an outer upper surface  20  which is formed from a composite material utilizing a resin, such as an epoxy resin, and fibers such as carbon fibers, Kevlar, S-glass, aramid fibers, or fiberglass, or a combination thereof. In one embodiment, as shown in FIG. 4, a thin epoxy carbon layer  21  is adhered to the upper surface of the deck intermediate core  22 . Core  22  is a honeycomb material having a thickness of about ⅜″. Alternate thicknesses can be employed within the scope of the present invention. Honeycomb core  22  is formed so that its outer peripheral edges  23  and  24 , leaving an extending deck flap  25 . Honeycomb is one type of core structure, but other materials of light weight and high structural strength may be used. The deck before joining has a deck peripheral edge  26 . 
     Core  22  has an upper surface  27  and a lower surface  28 . The outer composite layer  19 ′ has an inwardly facing surface  29 , which as shown in FIG. 4, is the lower surface of a composite such as a thin epoxy carbon layer  21 . Under the lower surface  28  of the deck intermediate honeycomb core  22 , is adhered to deck inner composite layer  31 . Layer  31  has a lower inwardly facing surface  32  and an upper surface  33 . 
     The bottom  11  similarly has an inner composite layer  34 , having a lower surface  35  and an upper inwardly facing surface  36 . The bottom intermediate core  37  has an upper core surface  38  adhered to the lower surface  35  of inner composite layer  34 . Bottom intermediate core  37  has a lower core surface  39  which is adhered to an outer composite layer  40 . Outer composite layer  40  has an inwardly facing surface  41  and an outer bottom surface  42 . 
     The board is shown in cross-sectional side view in FIG.  5 . The length, placement, shape, and overall configuration of stringer  14  provides an immense potential for control of the finished board flexibility. For instance, the distance between forward end  15  of stringer  14  and nose  43  affects the flexibility of the nose portion of the board. The larger this space, the more the nose will flex. Similarly, the distance between rear end  16  and tail  44  affects the flexibility of the tail. 
     The thickness of the stringer  14  also affects the flexibility of the stringer, and thus, the finished board. The choice of fabric also affects the flexibility and carbon fibers provide a stiffer stringer than does E-glass or Kevlar. Those of skill in the art will readily adapt aa myriad of combinations of stringer length, thickness, or outer fabric within the scope of the present invention. 
     As also seen in FIG. 5, stringer  14  may be tapered to fit the inner shape of the hollow board  10 . 
     While a single stringer is shown in FIGS. 1-5, a pair of stringers  45  and  46  may be used to provide stiffer rails. The rails are indicated by reference characters  47  and  48 . More than two stringers may be used in alternate embodiments. 
     A process of forming the board of the present invention is illustrated in FIGS. 7,  8 , and  9 . A shaped concave bottom mold  49  has an inner mold surface  50 . An uncured bottom portion, including an aluminum honeycomb core and two uncured composite layers, is surrounded by a vacuum bag  51 . A vacuum is drawn on vacuum bag  51 , which pulls the sandwiched uncured bottom against the inner mold surface  50 . 
     Similarly, shaped concave deck mold  52  has an inner mold surface  53  upon which a sandwiched aluminum honeycomb core surrounded by upper and lower composite layers is placed. A vacuum bag  54  surrounds the uncured deck  55 . Both the uncured deck  55  and the uncured bottom  56  are formed with outer peripheral flaps  57  and  58 , respectively. Once a vacuum is placed on vacuum bag  54 , the deck portion can be cured and the vacuum bags removed. 
     As shown in FIG. 8, the cured bottom  59  and the cured deck  60  have their inner surfaces exposed. Stringer  14  can be adhered to the lower inwardly facing surface  32  of cured deck  60 . Just before joining the deck and bottom halves, a polyurethane pre-foam strip  61  is placed on the upper inwardly facing surface  36  of bottom  59 . Before it rises completely, the bottom mold and deck mold are joined as shown in FIG.  9 . After joining, the polyurethane pre-foam strip  61  completes rising and forms a bond between the lower surface  18  of stringer  14  and the upper inwardly facing surface  36 . This area between the stringer  14  and the surface  32  is referred to as a contact area where the stringer  14  is adhered to the deck piece. The outer peripheral flaps  57  and  58  are joined with an epoxy or other appropriate adhesive. The assembly of FIG. 9 is cured, the mold has separated and the finished product appropriately finished. In place of the urethane prefoam, other adhesives may be used. 
     A cross-sectional view showing the bottom of surfboard  10  is shown in FIG.  10 . Surfboard  10  has a longitudinal axis  62  along which stringer  14  is aligned. For a surfboard having a 9′1″ length, a stringer having a length of 4′ has been found to provide an appropriate amount of flexibility. In this embodiment, prototypes having a space of 3⅓′ between forward end  15  and nose  43  and a space of 1⅔′ between rear end  16  and tail  44 , utilizing a 4′ stringer has proved a very satisfactory board. Of course, it is to be understood that the length of stringer  14  is variable, depending upon the requirement of the end user. 
     While a C-shaped stringer has been shown in the drawings, other shapes of stringers are also contemplated. An I-beam shaped stringer is shown in FIG. 11 and a rectangular stringer  64  is shown in FIG.  12 . 
     The end product is a surfboard of far less weight than conventional urethane foam cored surfboards. For instance, while a conventional board 9′ long would weigh between 18-20 pounds, the same length of board made by the process of the present invention would weigh less than 10 pounds. The nature of the invention is that it yields a surfboard which can weigh less than half that of conventional surfboards which is many times stronger and more durable. The reduction in weight allows the surfer to maneuver the board with proportionally less effort. This provides far greater handling less inertia in movement on a wave. 
     As shown in FIG. 13, vibration dampening layers  65  and  66  have been added on the upper and lower surfaces of stringer  14  to deaden vibration. 
     While the construction of a surfboard has been emphasized above, it is, of course, to be understood that the construction can be used for any hollow water supported object, such as wind surfers, wake surfers, kite surfing, wake boards, or sail boats. In these applications, the same combination of light weight, strength, and variable flexibility are very useful. 
     The present embodiments of this invention are thus to be considered in all respects as illustrative and not restrictive; the scope of the invention being indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.