Abstract: A boat hull or other marine structure is made by shaping a plastic foam core and covering it with a plastic outer skin glued in place by adhesive, mechanically fastened, or applied in liquid form. Minimal sawcuts to the foam core ease manufacture. Methods for anchoring fittings, masts, pipes and shade canopies are presented. No-sew sails for the boat have corners made of plastic sheet attached using both adhesive and mechanical fastening. Lateral resistance of the hull is provided by telescoping leeboards. A suite of these boats share the same modular masts and sails. Such boat hulls offer light weight, ease of transport, and unswampable buoyancy.