Square rig
Square rig is a generic type of sail and rigging arrangement in which the primary driving sails are carried on horizontal spars which are perpendicular, or square, to the keel of the vessel and to the masts. These spars are called yards and their tips, beyond the last stay, are called the yardarms. A ship mainly so rigged is called a square-rigger.
The square rig is aerodynamically the most efficient running rig (i.e., sailing downwind), and stayed popular on ocean-going sailing ships until the end of the Age of Sail. The last commercial sailing ships, windjammers, were usually square-rigged four-masted barques.
Terminology
Square-rigged masts may also have triangular staysails that are deployed fore-and-aft between masts.
The term "square-rigged" can also describe individual, four-cornered sails suspended from the horizontal yards, and carried on either a square-rigged or a mainly fore-and-aft rigged vessel, such as one with a bermuda rigged or gaff rigged mainsail.
"Square-rigged" is also used for the uniform of a rating in the Royal Navy since 1857. It is slang and refers to anyone wearing the famous blue square collar on the shoulders and bell-bottomed trousers. The name perhaps reflects the fact that it was these men who managed the square-rigged sails. The peaked cap uniform worn by Senior Ratings (Petty Officers, Chief Petty Officers and Warrant Officers) and Officers is known colloquially as 'fore-and-aft rig'.
