PURPOSE: To fold a catamaran not in its use to be transported and stored, by connecting a pair of floats, which are constituted by filling air in a bag body and holding its shape, with front and rear beams, connecting the beams to each other with a connection member and supporting a mast to an upper part of said member.

CONSTITUTION: A pair of floats 1 are connected to each other by front and rear beams 2, 3, and central parts of the beams 2, 3 are connected by a connected by a connection member 4, while the bottom end of a mast 6 of a sail 5 is connected and supported onto this connection member 4. The float 1 is constituted by rubber, plastic and other waterproof cloth material into a bag body, and air is filled to the inside of the float to hold it to a fixed shape. In this way, a whole unit can be folded, reassembled and formed to compact size when not in use to be convenient for transportation and storage.