Abstract: A rotatable pontoon includes a floating cylinder provided with watertight compartments and having a hollow interior for receiving one or more vessels adapted to be overturned by rotation of the pontoon. Rotation is achieved by either external power or by successively displacing water from one compartment to another. An external platform attached to the pontoon maintains a normal upright position during rotation of the pontoon and serves to contain accessory equipment. Alternatively, this equipment is attached to a belt surrounding the pontoon and fastened to stationary flotation tanks. Floating roofs are included to allow operation during rainy days and for removing load fractions remaining after a vessel is overturned, pushing panels and helicoidal hatch-feeders are provided.