Abstract: An ultralight yet extremely strong vessel without a circumferential support suitable for full-length, end-dumpable trailers, for railroad tank cars, highway tank trailer, refuse transportation vehicles and the like. High strength and minimum weight are achieved by arcuately stressing but light materials, by provision of longitudinal support members which may become an integral part of the vessel and, in open-top embodiments, by provision of a reinforcing member along an extended open edge of adequate horizontal moment of inertia and which may readily be pre-tensioned if desired. In the pre-tensioned embodiment, such to reinforcing member may cause the open-top vessel to bow inwardly before loading so as to compensate for the outward-tendency of such vessels constructed of elastic materials when loaded.