J Class yacht

A J-Class yacht is a single masted racing sailboat built to the specifications of Nathanael Herreshoff's Universal Rule, The J-Class are considered the peak racers of the era when the Universal Rule determined eligibility in the Americas Cup.

The J-Class is one of several classes deriving from the Universal Rule for racing boats. The rule was established in 1903 and rates double-masted racers (classes A through H) and single-masted racers (classes I through S). From 1914 to 1937, the rule was used to determine eligibility for the Americas Cup. In the late 1920s, the trend was towards smaller boats and so agreement among American yacht clubs led to rule changes such that after 1937 the International Rule would be used for 12-metre class boats.

The Universal Rule formula is: ${\displaystyle R={\frac {0.18\cdot L\cdot {\sqrt {S}}}{\sqrt[{3}]{D}}}}$

Where:

The numerator contains a yacht's speed-giving elements, length and sail area, while the retarding quantity of displacement is in the denominator. Also the result will be dimensionally correct; R will be a linear unit of length (such as feet or meters). J-Class boats will have a rating of between 65 and 76 feet. This is not the overall length of the boat but a limiting factor for the variables in the equation. Designers are free to change any of the variables such as length or displacement but must reduce the other variables if the changes derive a different rating (or they must designate the craft as belonging to another class).

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