The 12 Metre Class - Third Version - America's Cup 1958-1987

Twelve Metre yachts are quite possibly the most fascinating racing sailboats ever built. They have beauty and size that, along with their America's Cup history, has attracted and intrigued yachtsmen since their debut. The horsepower used to drive there 65,000 pound racing beauties to speeds as high as twelve knots lies in their massive sail area. Their mainsails are usually about 1200 square feet in size and their jibs, which can only have a height that is serventy-five percent of the mast in height, range from 500 square feet to over 1200 square feet in size. Twelve Metre yachts were not raced in the America's Cup until 1958. However, the six, eight, and twelve metre rules were developed over five decades earlier. In 1906 William Froude and Royal Yachting Association in England helped develop the International Rules for metre class boats. Before their America's Cip debut metre boats had considerable racing success and were used in the 1908, 1912, and 1920 Olympic games.

In 1958, after a twenty-one year halt of America's Cup competition, racing continued with a new class of racers, the 12 Metre Class. These 60 to 70 foot sloops were smaller in size, easier to crew, and more manageable on a race course than the previous 135 foor America's Cup racing class, J boats. However, the 12 Metre class like the J boats, were designed based on a formula. This meant that 12 Metre Class yachts could vary in sail area, lenght, and other speed production aspects. The following is the mathematical formula by which all 12 Metre yachts are measured that have been contructed since 1958.

L + 2d + SQR(S) - F / 2,37 = 12 Metres

L = waterline legnht (LWL)
S = sail area
d = difference between girth and chain
F = freeboard

This formula inputs speed producing factors through a simple mathematical formula. In order for a yacht to be Twelve Metre the result of this formula must not exceed 12 Metres. To limit the likelihood that one 12 Metre design would be vastly superios that another and promote fair and competitive racing there are other restrictions on design measurements of 12 Metre racing yachts. Maximum and minimum parameters on mast height, draft, beam and headsail height are applied to 12 Metre racing yachts to ensure that there is not too much diversity among boats.