sails atop shorter and wider boats leading either to unwieldy, and ultimately unsafe, boats or craft that simply were not competitive. In order to account, in some ways, for the beam and the relationship of the length overall () to the load waterline length the universal rule was proposed, taking into account displacement and length, which itself was a result of a formula taking into account such things as "quarter beam length". As different boats were designed and built, the notion of classes was derived to maintain groupings of competitive class. Following Sir Thomas Lipton's near success in the 1920 America's Cup, he challenged again for the last time at age 79, in 1929. The challenge drew all the novelties developed in the previous decade on small boats to be ported onto large boats, and pitted British and American yacht design in a technological race. Between 1930 and 1937, the improvements brought to the design of sailboats were numerous and significant: The high-aspect bermuda rig replaces the gaff rig on large sailboats Solid-rod lenticular rigging for shrouds and stays Luff and foot grooved spars with rail and slides replacing wooden hoops Multiplication of spreader sets: one set previously (1914), two sets (1930), three sets (1934), four sets (1937) Multiplication of the number of winches: 23 winches, Enterprise (1930) Electrical navigational instruments borrowed from aeronautics with repeaters for windvane and anemometer, Whirlwind (1930) "Park Avenue" boom (Enterprise, 1930) and "North Circular" boom (Rainbow, 1934) developed to trim mainsail foot Riveted aluminium mast (, Duralumin), Enterprise (1930) Genoa Jib (Rainbow, 1934) and quadrangular jib (Endeavour, 1934) Development of nylon parachute (symmetric) spinnakers, including the World's largest at on Endeavour II (1936) Duralumin wing-mast, Ranger (1937) All these improvements may not have been possible without the context of the America's Cup and the stability offered by the Universal Rule. The competition was a bit unfair because the British challengers had to be constructed in the country of the Challenging Yacht Club (a criterion still in use today), and had to sail on their own hull to the venue of the America's Cup (a criterion no longer in use today): the design for such an undertaking required the challenging boat to be more seaworthy than the American boats, whose design was purely for speed in closed waters regattas. The yachts that remain in existence are all British, and probably log more nautical miles today