Abstract: A method of forming a liner for a passage such as a sewer includes forming panels composing the liner using a neat resin of a first density and a polymer concrete of a second, higher density. The neat resin is inserted into a mold cavity before the polymer concrete and is displaced upwardly by the polymer concrete pour to impregnate a fiber layer disposed along the periphery of the mold cavity. Resulting panels preferably have an offset joint to increase the joint strength between upper and lower panels forming the liner.

Abstract: A mandrel-assisted resin transfer molding process and apparatus therefor provides a generally continuous, narrow annular channel between the perimeter of an inner male mold element and an outer female mold element. This channel allows air, heat and vapor to evenly escape and resin to outflow from the mold cavity everywhere around the edge of the part being molded. A very thin resin band forms in the channel is easily trimmed away, leaving the article completely finished on both sides and having a well defined edge that does not require shaping.

Abstract: A boat hull is provided with a unique V-shaped bottom surface to increase lift, to reduce drag, and to maximize speed. The deadrise angle of the V-shaped bottom increases progressively from the stern to a point forward of the stern at a rate of 2.degree. to 6.degree. for each four feet of keel length, i.e., at the rate of about 1/2.degree. to 11/2.degree. per foot of keel length. The bottom surface between the stern and the forward point has a generally convex transverse cross section. The keel is substantially straight from the stern to the forward point and then curves upwardly to the bow.