A buoyant structure with a hull, a main deck, a lower inwardly-tapering frustoconical side section; a lower generally rounded section extending from the lower inwardly-tapering frustoconical side section; a generally rounded keel; a fin-shaped appendage secured to a lower and an outer portion of the hull proximate the generally rounded keel. In embodiments, the keel has a first frame extending from the keel and a first keel extension connected to the first frame.