Later Melin worked out a much more advanced design, also perhaps never built: a large flyingboat with a pair of biplane wings set on top of the hull at each end; a glassed-in cockpit was in front, and a row of circular windows along each side. A pair of contra-rotating propellers was mounted on a pylon above the hull amidships; wingtips floats were attached to the tips of both lower wings, all of which were designed to fold.