PURPOSE: To complete the sealing of a piercing section by providing such an arrangement that a hull inner surface member is positioned close to a hull outer surface member in a scupper attaching position with an opening being formed in the close section, the peripheral edge section of the opening is sealed with a weather strip, and a scupper is attached to the hull outer surface member.

CONSTITUTION: A hull outer surface member 11 having a hull bottom 2 and a hull side 3, and a hull inner surface member 4 having a deck floor 5 and a gunwale 6 are made of FRP such that their outer surfaces are opposed to the surface of a mold. In the attaching position of a hull outer-shell piercing member for a scupper 8, the inner surface member 4 is positioned close to the outer surface member 1, and an opening is formed in the close section. The peripheral edge of the opening 7 is sealed with a weather strip 70, and as well the scupper 8 is attached to the outer surface member 1 opposing the opening 7. The sealing of the piercing section is ensured to prevent water from entering into between the hull inner and outer members 1, 4.