PURPOSE: To easily remove beams at disassembly from floats molded with each bag body, which holds a shape by filling air, by mounting the beam to holding members on the float through a recessed and protrusive fitting part to surely perform mounting while evacuating air in the bag body.

CONSTITUTION: A pair of floats 1 are connected to each other by beams 2, 3 longitudinally in two places, while the beams 2, 3 are mutually connected by a connection member, and a mast of a sail is supported to the beams 2, 3 or on the connection member, thus a small sailing catamaran is constituted. Each float 1 is constituted by a bag body holding its shape by filling air, and the beams 2, 3 are extended through penetrative holes 80 of holding members 8 provided onto the float 1 while connected through a recessed protrusive fitting part formed by a pin 70 of a supporting member 7 on the float 1. At assembly, the beams 2, 3 are surely mounted to the float by engagement between the recessed and protrusive parts, while at disassembly, the beams 2, 3 can be easily disconnected by evacuating air in the bag body 1.