PURPOSE: To obtain a hull which has excellent toughness and lightness by forming an middle layer out of plastics in which reinforcing materials are incorporated, and forming an inner layer and an outer layer between which the middle layer is put, using modified plastics in which additives and reinforcing materials are incorporated.

CONSTITUTION: This hull is comprised of an outer layer 1, a middle layer 2, and an inner layer 3, and the outer layer 1 and the inner layer 3 are formed out of plastics in which a basic material, polyethylene with additives and fillers are incorporated. The middle layer 2 is formed out of plastics in which a basic material, polyethylene with additives such as an antioxidant and reinforcing materials such as glass fibers are incorporated. A plastic foam rubber material is charged into the bottom 4 of the hull, a bow, a stern, and a buoyancy tank and so on. It is thus possible to increase, as a whole, performance such as lightness, toughness, impact resistance, and so on because the hull is comprised of three-layer structure which is all constituted of plastics.