(or "spanker") is a gaff-rigged, fore-and-aft sail, mounted on the after side of the mizzenmast. It was used to help tack the vessel. For square sails (from bottom to top): (fore, main, mizzen) ...sail, lower topsail, upper topsail, topgallant, royal, skysail. Choice of rig In the late 19th and early 20th centuries, choosing a sail plan for a displacement watercraft stemmed from the size and tonnage of the vessel, its purpose (working vessel, cargo vessel or yacht) and the anticipated winds in the region where it was expected to sail. In that period, sail plans might start from smallest to largest boat or ship in a hierarchy of sailing rigs: Yachts Catboat with a single sail Sloop with mainsail and jib Yawl with a small mast behind the steering post Ketch with a mizzenmast ahead of the steering post Working boats and coastal freighters Cutter with a single mast and multiple headsails Schooner with two or more masts Ocean-going merchant vessels Brig with two square-rigged masts Brigantine with square-rigged foremast and fore-and aft mizzen Barque with two square-rigged masts and a fore-and-aft mizzen Barquentine with one square-rigged mast and two fore-and-aft masts behind Full-rigged ship with three or more masts with square sails on each Gallery The following sail plans are at various scales. See also Sailing rigs References