PURPOSE: To form an attaching part without the strength of an FRP hull being reduced, by piercing a coupling member comprising a shank part and a head part through the bottom of the hull from the outside of the hull, and by forming, in the shank part, a coupling part for an inboard side component part while the head part is made abut against the bottom surface of the hull.

CONSTITUTION: A coupling member 8 is made pierce through the bottom of a hull which is formed by covering a core material made of foamed plastic material 2 with FRP outer skins 5, 6 from the outboard side of the hull, and therefore is secured to the bottom of the hull. The coupling member 8 is composed of a shank part 50 and a head part 81. The head part 81 is projected in the direction perpendicular to the axis of the coupling member 8, and is made into contact, at its back surface 83, with the hull outer skin 6. A nut 82 is fitted onto the front end part of the shank part 80, and is engaged with the front end thread section of a shaft 70 for attaching a locking band 3 for passengers. Thereby, the attaching part may be formed without the strength of the hull is reduced.