PURPOSE: To improve the joining workability and strength of long members by forming a stepped support surface at one end of any of first and second members which are joined together, joining another end thereof on the support surface, and applying strips across the surfaces of both ends.

CONSTITUTION: A small-sized ship A comprises a first member 1a forming the half part of the stern side and a second member 1b forming the half part at the bow side, both members being formed by an FRP material and joined 10 at the substantially central part of the hull. Upon this occasion, the first member 1a forms at its joined end a stripping allowance 12 recessed through a stage 12' from the main body surface 11 and a support surface 13 recessed further through a stage 13' from the stipping lug 12. On one hand, the second member 1b forms integrally a stripping allowance 16 recessed through a stage 13' from the main body surface 15, and the stripping allowance 16 is placed on the support surface 13. Upon joining, both members are joined through a FRP mat 17 in which a mischmash or the like is impregnated thereby to seal both members by applying strips 18.