International Rule - changes from 1895-1933

Yacht racing - rating and design

[Note, The following was valid as of 1935. All measurments use the imperial (ft., lbs.) system. Ed.]

1895

The conditions in Great Britain following the advent of the bulb-fins Niagara and Isolde, and the construction of similar yachts to meet them, led to earlier action than in America, and on June 17, 1895, the Yacht Racing Association adopted the following formula, proposed by R. E. Froude, to take effect on January 1, 1896,

L + B + 0.75G + 0.5√SA             = Rating.
                    2                  

The new factor G represented the skin girth, from waterline to waterline, the resulting unit being termed "Linear Rating". In the meantime one of the many attempts at an association in the United States and Canada had been launched in 1897 under the name of the Yacht Racing Association of North America. After an investigation and a visit abroad by two of its representatives it adopted this "Girth Rule," which was used by some of the smaller clubs, but the larger American clubs would not accept it.

1901

As the "Girth Rule" in its original form failed to effect the desired end, the promotion of a larger area of midship section, it was amended in 1901 by the addition of "chain girth" to "skin girth" and the further addition of d, the difference in feet between the two girths. This new rule, proposed by Alfred Benson, a Danish yachtsman, was adopted for seven years from January 1, 1901, the formula being

L + B + 0.75G +4d + 0.5√SA             = Rating.
                      2.1                    

1906

In 1906 an international conference of European nations was assembled in London at which was adopted what is now known as the "International Rule", a new factor F representing the mean of the freeboard amidships and at the ends of the waterline, being added:

L + B + 0.5G +3d + ⅓√SA             = Rating.
                     2                    

1919

This formula was amended in 1919, after the Great War when yacht racing resumed, the new form being

L + 0.25G + 2d + √SA -F             = Rating.
                  2.5                  

In 1934 a change was made in the measurement of the freeboard at the ends of the waterline, but apart from this detail the formula is as above in 1935.