Abstract: A structure consists of an intermediate platform surmounted by at least one chamber of spherical or partially spherical form occupying a relatively major portion of the platform upper surface, and a plurality of smaller chambers on the underside of the platform. The preferred construction of the chamber walls is single panel monocoque. When used as a boat, the lower chambers may be buoyancy chambers. A string of such boats are well adapted for ocean-going transportation. The structure may be insulated and reinforced by the application of an interior layer of polycarbonate foam. Three or more underside chambers in mutually spaced apart relation constitute flotation chambers on which the vessel is supported. The chambers provides efficient, stable buoyancy, and promote effective streamlining for ease of movement over the water. Smaller versions may form play houses; miniature versions may serve as play toys.