America's Cup Racing Yachts
Evolution of a Design - The Magnificent J-Class
W. Starling Burgess & Owlin Stephens' J-Class Ranger
Although they became recognized the most beautiful yacht design in the World, only 10 J-Class yachts were ever built - 6 in the USA and 4 in the UK. Most of
these competed in trials for the America's Cup, or competed in the Cup itself. Other yachts (pre J-Class) were converted to meet the rule requirements.
Name              Built            Designer                       AC Role               LWL          LOA            Beam        Draught      Displacement      Sail Area
Enterprise       US 1930   W. Starling Burgess     1930  Defender      80ft            120ft 9in       23ft          14ft 6in       128 tons               7583 sq-ft
Whirlwind      US 1930    L. Francis Herreshoff                                  86ft            130ft             21ft 9in    15ft 6in       158 tons               7335 sq-ft
Yankee            US 1930   Frank Paine                                                   83ft            126ft             22ft 6in     14ft 6in      148 tons               7288 sq-ft
Weetamoe       US 1930   Clinton Crane                                                83ft            125ft 9in       20ft           15ft            143 tons               7550 sq-ft
Shamrock V    UK 1930  Charles Nicholson         1930 Challenger    81ft 1in      119ft 1in       20ft           14ft 9in       134 tons              7540 sq-ft
       UK 1932  Charles Nicholson                                        83ft             127ft 6in       21ft 6in     15ft            160 tons             7541 sq-ft
Endeavour     UK 1934  Charles Nicholson         1934 Challenger    83ft 6in      129ft 6in        22ft           14ft 9in      143 tons             7561 sq-ft
Rainbow         US 1934   W. Starling Burgess      1934  Defender      82ft            127ft 6in        21ft          15ft            141 tons              7535 sq-ft
Ranger            US 1937   Burgess & Stephens     1937  Defender      87ft            135ft              21ft          15ft            166 tons              7546 sq-ft
Endeavour II  UK 1936  Charles Nicholson         1937 Challenger    87ft            135ft 6in       21ft 6in     15ft            162 tons              7543 sq-ft
where R = rule length (76 ft), L = LWL (ft), S = Sail area (sq-ft), D = Displacement (tons)

The J-Class had a maximum rating of 76 feet and a maximum allowable waterline length of 87 feet. During the 1930s, it was found that the longest-waterline
boats were the fastest. Both
Ranger and Endeavour II were built to the maximum waterline length of 87 feet. Owlin Stephens undertook a model-testing
program during the development of
Ranger. The models were given design numbers 77-A through 77-F, and 77CE. While the models all had 87-foot
waterlines, they had different beams, displacements, longitudinal centers of buoyancy, prismatic coefficients and wetted areas. As with modern America's Cup
Class yachts, the J-Class designs were optimized for the conditions they were expected to sail under. The final lines for
Ranger were derived from model 77-C
which was believed to be the best suited for racing off Newport, RI (where the America's Cup  races were held from 1920 through 1983) where summer winds
are light and seas relatively small.
Ranger's final lines were modified from the model 77-C lines most noticeably in the 'hooked bow' that can be found on the
1937 America's Cup winner.
The J-Class was based on the American Universal Rule which took into account length, sail area and displacement. Roughly,
R = 0.18 L square-root(S)/cube-root(35D)
Ranger J5 in 1937