Ships – Boats – boat component – or attachment – Hull construction
Reexamination Certificate
2001-07-13
2003-05-13
Avila, Stephen (Department: 3617)
Ships
Boats, boat component, or attachment
Hull construction
C441S074000
Reexamination Certificate
active
06561118
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 that meet at the perimeter and thereby delimit an internal cavity; the concave, female surface of the mold defines the board's exterior shape, and imparts a smooth surface to the exterior 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 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 blank molds for surfboard production, and frequently leaves insufficient foam in the nose and tail areas of the 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 molded-in rocker curvature produced by the more than sixty blank molds offered for surfboard production. Molding the density-gradient into the foam and providing the frequent lengthwise rocker modifications are expensive but essential, because the board's ability to withstand impact and bending loads 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 ad top and bottom spar caps (i.e. the top and bottom reinforcing flanges in an I-beam)—the lack of effective longitudinal reinforcement leaves thinner surfboards in particular susceptible to breakage. In custom-board production, a basic problem is the one-to-one weight ratio of skin material to interior core. Currently, enhancing the strength-to-weight ratio entails the high costs and lengthy mold cycle of a fiber-reinforced structural sandwich skin, in the more expensive of the two basic methods of molded manufacture outlined briefly below.
b. Molded Methods of Production
The rapid mold-cycle and inexpensive thermoplastic skin of a blow-molded, rotationally-molded, or vacuum-formed board generally offers lowest costs of production. The specifications of U.S. Pat. No. 5,094,607 to Masters and U.S. Pat. No. 4,065,337 to Alter et. al, which describe rotational and vacuum thermoforming methods applicable to surfboards, sailboards and other small watercraft, are incorporated herein. U.S. Pat. No. 4,713,032 to Frank, the specification of which is incorporated herein, is directed to low-cost methods in which a fiber-reinforced resin foams to fill the void between a pre-molded EPS core and the surface of the closed mold. Using quick-setting, foamed polyurethane resin in the skin, the cited invention achieves 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.
In the above methods, the strength of the fiber reinforcement is greatly reduced by the foaming of the resin matrix, or is absent altogether. Using a rotational mold, three separate charges of resin, the second of which foams, are often used to create a thicker, stronger skin “sandwich skin;” similarly, a thin sheet of PVC foam is often used as a sandwiched core between the layers of laminate to create a fiber-reinforced, foamed plastic sandwich skin.
Due to the inherent weakness of the above materials, strength-to-weight and skin-to-interior core ratios fall well below expensive, high-performance sailboards, that eliminate the blowing agent in the fiber-resin to create a much higher strength “structural sandwich” skin. The structural sandwich is expensive to fabricate because of the very long mold cycle—vacuum pressure is used to eliminate entrapped air and voids and causes the sandwich core/laminate to conform to the shape of the mold; to prevent the spring-back of the sandwich core the material remains in the mold under vacuum pressure for about two to three hours, until the resin has completely cured. The shape of the opened mold creates an additional problem—the sharp, concave edge contours tend to create a dam, and the sandwich core layer, by blunting the effectiveness of the squeegee in removing excess resin from the laminate, prevents the skin from attaining optimum strength and lighter weight.
In the interior core, EPS (expanded polystyrene) bead foam requires separate pre-molding in a steam chest, but is preferred over polyurethane foam due to its lighter weight-containing the expansion of liquid polyurethane pre-foam injected into the mold's interior generally requires an extremely strong mold, steel reinforcing jigs and a hydraulic press to prevent mold distortion or buckling under the high pressure. In prior art described in U.S. Pat. No. 5,023,042 to Efferding, the wet epoxy laminate/PVC sheet foam of the structural sandwich skin fits into molded-in recesses in the EPS core and the entire assembly is placed in the mold, the exterior of which 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) may be applied using the evenly flexing upper mold half disclosed in the invention to Efferding, which eliminates distortion problems by compressing the EPS interior core evenly, creating a permanent compression set of about three sixteenths of an inch in the finished board. Internal shear webs, spars, etc. become problematic, however, as they tend to cause distortion problems to reappear under vac
Avila Stephen
Hughes Michael J.
Intellectual Property Law Offices
LandOfFree
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