During the 1930s J-class yachts were built to race in the America's Cup. Only 10 were ever built as they were extremely expensive to build and maintain, especially in the post war years. They succeeded the 1883 Seawanhaka Rules 75-footers of 1920 and were replaced by the 12 - metre class yachts when the Cup was challenged again in 1958.
The J designation refers to the class of yacht defined by its sail area, displacement, length, and mast height, formally defined in the Universal Rule. When designing a J-class yacht builders would have to decide which characteristics to maximize to build the ideal yacht.
All three America's Cup races featuring J-class boats were won by the New York Yacht Club. In 1930 Enterprise defeated Shamrock V of the Royal Ulster Yacht Club. In 1934 Rainbow defeated Endeavour of the Royal Yacht Squadron. In 1937, at the peak of J-class racing, the "Super J," Ranger defeated Britain's Endeavour II.
Only three of the original yachts are still sailing today; Shamrock V, Velsheda and Endeavour. They have all undergone extensive restoration and rebuilding.
A replica of Ranger was launched in 2004. As of April 2008 another three yachts are being built or planned. These are Endeavour II, Lionheart and Svea. According to J-class regulations, any new yacht built must use existing designs from the 1930s.