To narrow width between catamaran bodies without disassembly and to ensure easy transportation on the roof of a car, not a truck, by rotatably axially connecting the rear ends of respective crossing links of an X-shaped crossing link-type connector to the catamaran bodies and by back and forth movably and fixedly connecting to the cataraman bodies.

Relaxation is made to fastening by the fastening members of pivot parts at the frond ends of respective link members 4, 4 in an X-shaped crosslinking type connector 3. Moving bodies 8 are moved along guide members 2. Forwardly moving the moving members 8, 8 and narrowing the X-shaped crosslinking type connector 3 approach the width between catamaran bodies 1, 1. Thus, loading on a car is possible under this state, and travelling like a monohull type yacht is possible. In addition, use for board sailing in available. Especially, in this state, narrowing the opening of the X-shaped crosslinking type connector 3 enables automatic forward movement instead of forwardly displacing the position of a mast compared with the use as a yacht.