A buoyant structure contains a hull having a main deck, a lower inwardly-tapering frustoconical side section that extends from the main deck, a lower ellipsoidal section extending from the lower inwardly-tapering frustroconical side section, a keel having an n-polytope shape, a fin-shaped appendage secured to a lower and an outer portion of the exterior of the keel having the n-polytope shape, and a plurality of columns connected between the keel having the n-polytope shape and the main deck forming one or more tunnels between the plurality of columns.