Buoys – rafts – and aquatic devices – Water skimming or walking device – Surfboard
Reexamination Certificate
2001-01-12
2003-09-23
Avila, Stephen (Department: 3617)
Buoys, rafts, and aquatic devices
Water skimming or walking device
Surfboard
C114S357000
Reexamination Certificate
active
06623323
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods and apparatus used in the design and manufacture of surfboards, sailboards or similar aquatic boards, referred to generically herein as “board” or “boards.”
2. Description of the Related Art
Surfboards and sailboards are of similar shape, however the sailboard is generally manufactured in a mold, while the surfboard is fabricated using a labor-intensive moldless or custom method of construction. The conventional molds used in surfboard and sailboard construction comprise top and bottom halves, with a part line at the point of greatest breadth along the board's perimeter edge or rail, and utilize the mold's concave, female surface to define the shape of the board, and impart a smooth surface to the fiber-reinforced plastic skin. Currently available molded production techniques restrict the shape of the board to an exact duplicate; which generally limits molded production to the less demanding design of the sailboard. For molded surfboard production, the very wide variation in size and shape requires the manufacturer to invest in a large and prohibitively expensive inventory of molds, and eliminates the many custom design modifications that are made in the prior art as a matter of routine.
a. Moldless, or Custom Board Production
The surfboard is typically constructed without a mold. The board is individually hand-shaped from a polyurethane foam blank, and the fiberglass and resin are applied by hand over the shaped foam core. The process is labor-intensive, requires considerable skill, and involves structural problems that dictate dividing the production process into two separate steps, with the foam blank supplied by a separate manufacturer.
To enhance the strength of the foam, the blank is molded in an extremely strong, heavy mold made of reinforced concrete. This allows an excess of liquid pre-foam to be poured in the mold; as the foam expands, the excess compresses under high pressure against the surface of the mold and produces a density-gradient in the blank—the foam is soft and weak in the center and becomes progressively harder and denser towards the surface. To avoid removing too much of the harder, denser surface foam during shaping, the blank is molded close-to-shape, or as thin as possible. This close-to-shape molding has the drawback of increasing the requisite number of molds for surfboard production, and frequently leaves insufficient foam in the nose and tail areas of blank for the shaper to produce the desired lengthwise bottom curvature or rocker in the board.
The molded in rocker of the blank must therefore be modified by the blank manufacturer by gluing the blank to a wooden center spar or stringer cut to dimensions specified by the customer, and usually selected from a list of stock lengthwise rocker modifications. Clark Foam of Laguna Niguel, Calif., (www.clarkfoam.com) lists in its Rocker Catalog the dimensions of over two thousand different templates available to modify the lengthwise curvature of the more than sixty blank molds offered for surfboard production. Producing density gradient in the foam and producing the frequent lengthwise rocker modifications are necessary to maintain an adequate level of strength on the board significantly increase the costs of production but are essential, because the board's impact resistance is very low.
The single fiberglass ply used on the bottom of the board will usually dent or fracture with moderate finger/thumbnail pressure, while the double or triple layer used to reinforce the deck (or top surface of the board) in the tail area where the rider stands often fatigues, becomes permeable to water, then fails and completely delaminates under the repeated high pressure of the rider turning the board. Shaping also limits the effectiveness of the longitudinal reinforcement—it makes wood the material of choice for the center spar and also makes it impractical to add top and bottom spar caps—the lack of effective longitudinal reinforcement leaves thinner in particular susceptible to breakage.
The fundamental problem is the one-to-one weight ratio of skin material to interior core. With current methods of production, the only practical method of improving this ratio and enhancing the overall strength-to-weight ratio of the board is to use the second and more expensive of the two basic methods of molded sailboard construction outlined briefly below.
b. Molded Methods of Production
The methods of molding that offer very low overall costs of production typically employ a blow-molded or thermoformed skin of pure plastic, or lightly foamed, fiber-reinforced plastic, and generally produce boards with excessive weight or an inadequate level of strength. An illustration of low production costs, however, is provided by the U.S. Pat No. 4,713,032 to Frank, the specification of which is incorporated herein, which uses quick-setting foamed polyurethane resin in the skin to achieve a rapid mold-cycle of about twenty minutes per board and high production from the molding tool of as many as twenty-four boards per day. The light foaming of the resin matrix greatly reduces the tensile strength of the reinforcing fiber, however, which leaves strength-to-weight and skin-to-interior core ratios well below expensive high performance sailboards that employ a “cored composite” or “structural sandwich” skin.
The core in the structural sandwich—usually a thin layer of high-density plastic foam—spaces apart the two layers of high-strength laminate on either side so that the skin delivers the strength and stiffness of much thicker material, but at a fraction of the weight. The sandwich skin is expensive to fabricate because of the very long mold cycle—vacuum pressure is used to cause the skin material to conform to the shape of the mold, to prevent any spring-back of the skin core the material must remain in the mold under vacuum pressure for about two to three hours, until the resin has completely cured. The added drawback is that the difficulty removing excess resin from the laminate usually prevents the skin structure from attaining even higher strength and a further reduction in weight.
For example, when the laminate is saturated in the shallow, concave interior of the opened mold, the mold's shape is a problem because the sharp edge contours create a dam, and the addition of the sheet foam skin core layer creates a buffer that significantly reduces the effectiveness of the squeegee on the interior layers of laminate. When the skin is fabricated first, the core of the board is formed by injecting liquid polyurethane pre-foam into the interior of the closed mold, the drawback being that this requires an extremely strong mold; the halves are typically attached to steel reinforcing jigs and held in a hydraulic press to prevent the mold from distorting, buckling or separating under the high pressure.
A more common method of sandwich skin fabrication is to use a lighter weight, pre-molded core of EPS (expanded polystyrene bead) foam. In this method the wet epoxy laminate/PVC sheet foam of the sandwich skin fits into molded-in recesses in the EPS core and the entire assembly is placed in the mold, the exterior of which then precludes resin removal by hand. Vacuum is applied to press the components tightly together and squeeze excess resin out in the process, but the pressure is limited to about 12-15 inches of Hg to prevent the mold from distorting and the foam core collapsing. Full vacuum (27 in. Hg) can be applied using the mold disclosed in the U.S. Pat. No. 5,023,042 to Efferding, the specification of which is incorporated herein, which provides an evenly flexing upper mold half that eliminates distortion problems by creating a completely even, permanent compression set of about three sixteenths of an inch in the finished board. This requires an interior core of uniform density, however; internal shear webs, compression inserts in the tail area, or hollow, weight-reducing chambers in the interior are problematic, as they tend to exacerbate
Avila Stephen
Hughes Michael J.
IPLO -Intellectual Property Law Offices
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