at sea, is a term used by the steer's-man, when the main-sail, foresail, or sprit-sail, hinders his seeing to steer by a land-mark; upon which he calls out, Duckup the clew-lines of these sails; that is, hale the sails out of the way. Also when a shot is made by a chance-piece, if the clew of the sprit-sail hinders the flight, they call out, Duckup, &c.