Abstract: A boat, especially a catamaran, having a rectangular collapsible frame with a one-man mast stepping structure. The tubular frame is comprised of fore, aft and central sub-frame assemblies which can be collapsed so as to be easily car topable and serve as a rack for containing other components of the catamaran. Inflatable hulls are secured in bracket arches on the undersides of the sub-frame assemblies. A rudder frame or cage is pivotally mounted on an aft sub-frame assembly and is adapted to receive a rudder, which is identical to and interchangeable with daggerboards. A system of adjustable rope stays is provided for adjusting the mast.