a brace on a square-rigged ship is a rope ("line") used to rotate a yard around the mast, to allow the ship to sail at different angles to the wind. braces are always used in pairs, one at each end of a yard ("yardarm"), termed port brace and starboard brace of a given yard or sail (e.g., the starboard main-brace is the brace fixed to the right end of the yard of the main sail).