Fantail: the overhanging part of a ship's stern, a term used particularly in the case of large yachts and passenger liners. Although the correct word for the stern overhang of all ships, it is not often used in this connection except in the U.S.A. It has not quite the same meaning as counter, but comes very close to it. [The Oxford Companion to Ships and the Sea, Kemp, editor, 1976, Oxford University Press]
Fantail: The aftermost part of a ship, usually of the main deck; at the extreme stern. This word is believed to be purely American, from the early days of elliptical (fan-shaped) sterns, the mid XIX. [Origins of Sea Terms, John G. Rogers, Mystic Seaport Museum, Inc., 1985 (2nd ed.)]
These definitions don't do justice to the grand image of the classic fantail motoryacht. A very popular style for yachts built in the Roaring Twenties, the fantail stern evoked images of the grand trans-Atlantic liners and provided a perfect platform for elegant parties or breakfast at anchor on a quiet summer morning.
Of course, it's not just the stern shape that is important. Coupled with a plumb bow, stately cabins and a purposeful wheelhouse, the result was an efficient and comfortable cruiser at home in any marine setting.