PURPOSE: To obtain a ship body with rich buoyancy, by fully arranging a reinforced fiber cloth in a mold, locating a float of small specific gravity to a prescribed position, and the sucking air in the mold with a vacuum pump while injecting plastic thus preparing the ship body.

CONSTITUTION: A gel coat layer 2 is formed by a spray gun on internal surfaces of a ship body shaped internal mold 1, and a reinforced fiber cloth 3 is arranged on said layer along the internal surface of the mold. A float 4 with specific gravity not more than 0.06 and an embedded plate 44 are arranged on the cloth 3, covered with the reinforced fiber cloth 3 and capped with an external mold 5 from the above then fixed. Both injection resin from an injection port and sucking air from the air suction port 51, the resin is uniformly distributed in the mold to form a ship body.