A buoyant structure has a hull having a main deck. The hull further contains a lower inwardly-tapering frustoconical side section that extends from the main deck, a lower generally rounded section extending from the lower inwardly-tapering frustoconical side section, a generally rounded keel, and a fin-shaped appendage secured to a lower and an outer portion of the exterior of the hull proximate the generally rounded keel, the fin shaped appendage having a shape selected from the group consisting of: a triangular shape, a hump shape and a pair of connected triangular projections shape.