A historic nuclear-powered ship that probably attracted more barnacles than tourists while serving as a floating museum off Mount Pleasant has completed the first leg of its rehabilitation. But the next phase of work won't take place in the Lowcountry, as federal officials had once considered. The NS Savannah, the world's first nuclear-powered cargo and passenger vessel, is being restored, possibly for its second stint as a floating museum, according to its owner, MarAd. Colonna's Shipyard in Norfolk, Va., recently completed an initial $995,000 cleanup and renovation of the 596-foot ship, which was declared a National Historic Landmark in 1991, when it was still part of the naval museum at state-owned Patriots Point in Mount Pleasant.