Abstract: A catamaran has a collapsible frame and a pair of elongated pontoons spacedly secured in collapsible frame. The frame includes fore and aft cross bar sub-frame members and a pair of longitudinally extending sub-frame members and a support platform supported on the frame. Each said longitudinally extending sub-frame member being molded and including a pontoon embracing longitudinal cavity which is the length of the longitudinally extending sub-frame member, and a pair of parallel longitudinal edges, one longitudinal edge at each side of the longitudinal cavity, respectively. A first of the longitudinal edges has a slot therein and the other of the longitudinal edges has a shape complementary to the longitudinal slot whereby pairs of longitudinal edges of the pair of molded sub-frame members, respectively, can interfit such that the concavities face each other to form a storage space for the pontoons and the fore and aft tubular sub-frame member when not in use.