Square sail

Square rig is a generic type of sail and rigging arrangement in which a sailing vessel uses square sails which are carried on horizontal spars that, when at rest, are perpendicular (or square) to the centre line of the vessel. This is in contrast to fore and aft rig, where the sails are on the vessel's centre line when at rest. A consequence of this is that square sails have a front and a back surface, with the back always facing the wind when used to drive the ship forward, whilst fore and aft sails have a left and right surface, either of which may face the wind. The majority of square sails are symmetrical about an axis parallel to the mast, whilst most fore and aft sails are asymmetrical in shape.