A buoyant structure having a hull, a planar keel defining a lower hull diameter, a lower cylindrical portion connected to the planar keel, a lower frustoconical portion disposed above the lower cylindrical portion with inwardly sloping wall at a first angle, an upper frustoconical portion directly connected to the lower frustoconical portion, and the upper frustoconical portion with outwardly sloping wall, the inwardly sloping wall abutting the outwardly sloping wall forming a hull neck with a hull neck diameter. The buoyant structure having a main deck, a moon pool, and propellers attached to the planar keel, which are operated by a motor or a generator. The buoyant structure connects over a chambered buoyant storage ring.