PURPOSE: To endure against a contamination due to adherence of an ocean organism and to be usable at an underwater surface by supplying a material layer to a mold to form a non-biocidal antifouling material layer on an outermost layer of a boat hull.

CONSTITUTION: A non-biocidal antifouling material layer is supplied to a mold to form a non-biocidal antifouling material layer on an outermost layer of a boat hull. In this case, before resin is completely cured, the material layer is supplied to an outermost layer of the resin on a dipping type mold. And, at least non-biocical antifouling material has fine grooves extending in a longitudinal direction of the hull in such a manner that a width of the groove is 10 to 500 microns and a width of the groove is 5 to 100 microns. A surface of the hull of non-biocical antifouling material maintains a reduction in a frictional drag given by the groove or riblet by using for a long period under water.