A rope or chain fastened to one or both the lower corners of a sail, to extend and retain the clue down to its place. When a ship sails with a side wind, the lower corners of the main and fore sails are fastened by a tack and a sheet, the former being to windward, and the latter to leeward; the tack is, however, only disused with a stern wind, whereas the sail is never spread without the assistance of one or both of the sheets; the staysails and studding-sails have only one tack and one sheet each; the staysail-tacks are fastened forward, and the sheets drawn aft; but the studding-sail tacks draw to the extremity of the boom, while the sheet is employed to extend the inner corner.