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