batten down the hatches, to

To get ready for trouble. A nautical term dating from the early nineteenth century, it signified preparing for bad weather by fastening down the battens, strips of wood nailed to various parts of masts and spars, and fastening tarpaulins over the ship’s hatchways (door- ways and other openings). The term began to be used figuratively as preparing for any emergency by the late nineteenth century. See also CLEAR THE DECKS.