<P> A mast is considered square - rigged if its lowest sail or course is square - rigged, but normally if this is the case it will have a complete set of square - rigged sails . If the course is fore - and - aft, square topsails can still be carried in front of the mast . </P> <P> In their heyday, square - rigged vessels ranged in size from small boats to full rigged ships . But this rig fell from favour to fore - and - aft gaff rigs and bermuda rigs after the development of steam power and new materials . Ocean - going sailing ships stayed mostly square - rigged . </P> <P> Square rigs allowed the fitting of many small sails to create a large total sail area to drive large ships . Fore - and - aft could be sailed with fewer crew and were efficient working to windward or reaching, but creating a large total sail area required large sails, which could cause the sails and cordage to break more easily under the wind . 18th century warships would often achieve tops speeds of 12--13 knots (22--24 km / h), although average speeds over long distances were as little as half that . Some clipper ships that had square rigs and for whom speed was critical could be much faster; for example Cutty Sark could make 17 knots (31 km / h). The late windjammers were as fast as the clippers, being much bigger . </P> <P> Not only could a smaller sail be managed by a smaller crew but also these smaller sails constrained the impact of weapons on them . A hole from a cannonball affected only one sail's area, whilst a hole in a large sail would eventually tear the whole larger area and reduce more of the vessel's motive power . </P>

Horizontal part of square rigged vessel mast crossword clue