PURPOSE: To enhance adhesive power and prevent a bonded part from being broken by expansion or contraction due to temperature changes, by fuse-bonding the opposed surfaces of plastic-made protectors for a hull on each other.

CONSTITUTION: Fenders 7 are mounted on a gunwale 8 by bolts 9 so that the opposed bonded surfaces 7a of the fenders 7 can be thrusted on each other. The bonded surfaces 7 remain separated from the gunwale 8 before the surfaces 7a are fuse-bonded on each other. A high-temperature heating plate 10 is sandwiched between the surfaces 7a to heat them simultaneously. After it is confirmed that the bonded surfaces 7a are molten enough, the heating plate 10 is pulled out and the surfaces 7a are bonded on each other.