1.  Field of the Invention
The present invention relates to the construction of hulls for a catamaran and more particularly to a molding process for reinforcing the hulls so that they are not only lightweight, but are also strong by using a set of internal ribs. 
2.  Description of the Prior Art
U.S. Pat.  No.  3,971,837, entitled Process for Manufacturing a Composite Foamed Synthetic Resin Bowling Pin, issued to Tadashi Hasegawa on July 27, 1976, teaches a method of manufacturing a composite foamed synthetic resin bowling pin.  The use of foam material to provide structural strength to a plastic body is presently in common use in many sporting apparatus including its use in reinforcing the fiberglass hulls of a small catamaran. 
U.S. Pat.  No.  2,816,298, entitled Boat Construction, issued to Joseph F. Foster on Dec. 17, 1957, teaches a hull which includes an outer skin and an inner shell and which also includes a corrugated filler sheet positioned between the inner shell and the outer skin. 
U.S. Pat.  No.  4,021,874, entitled Boat Hull, issued to Hobart L. Alter and Peter L. V. Hutchinson on May 10, 1977, teaches a boat hull which is fabricated from synthetic plastic sheets.  The main deck of the hull is separately vacuum-formed.  Plastic foam is adhered onto the interior surfaces of the sheets.  The main body and hull are thereafter joined along the gunwale. 
U.S. Pat.  No.  3,811,141, entitled Boat Hull and Deck Assembly, issued to Helmut Stoeberl on May 21, 1974, teaches plastic boat hulls which are co-nected to the deck through nested inter-fitting tongue and groove joint configurations which are bonded together.  U.S. Pat.  No.  3,648,310, entitled Boat Structure, issued to Frank W. Butler on Mar. 14, 1972, teaches another boat structure which is useful in a dual hull boat arrangement and which has a pair of spaced hulls and a deck with a downwardly depending skirt which fits over the pair of spaced hulls. 
The hulls of a catamaran are presently constructed in two pieces, one piece forming the top portion thereof and the other piece forming the bottom porion thereof.  There is a mold for each piece.  The molding process of each piece includes the steps of waxing the inner surface of the mold and coating the waxed surface with a polyester paint.  The molding process also includes the steps of placing a layer of fiberglass and polyester resin onto the waxed and coated surface so that the layer will bond and cure to the coating of polyester paint, once the layer has bonded to the coating and has cured, placing a layer of foam material coated with a polyester resin on the layer of fiberglass and polyester resin, and pressing these two layer together by a vacuum technique.  A vacuum system pulls the foam material against the inner surface of the layer of fiberglass and polyester resin.  The molding process further includes the step of placing another layer of fiberglass and polyester resin onto the layer of foam material.  Once this layer has bonded to the layer of foam material and has cured, the mold is removed and one of the portions of the hull is ready for assembly. 
When both the top portion and the bottom portion of the hull have been formed they are joined together along their peripheral edges and secured by glue to each other.  The joint formed where these two portions join is structurally weaker than the sidewalls of the hull because there is no continuity in the layer of foam material and there is no interlocking between the edges of the two portions of the hull.  Furthermore the joint does not effect a smooth surface.  In addition to the problem of structural weakness, there is another problem in that the peripheral edges of the two portions of the hull must be aligned in order to effect a joint that is a smooth as possible.  This is a problem where the two portions of the hull are mass-produced each in one place and assemble in still another place.  Both of these problems are results of the method used to mold each portion of the hull which produces a relatively thick sidewall and the method of joining the two portions of the hull which necessitates an alignment thereof. 
The inventor has developed two methods for molding the portions of a hull for catamaran.  The methods in and of themselves are useful in that each solves one of the above-mentioned problems.