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The '''Universal Rule''' determined a [[yacht]]'s eligibility to race in the [[America's Cup]] from 1914 to 1937. Boats built according to the rule reached their peak in the large [[J-class yacht]]s. 
Before 1914, the [[Seawanhaka Corinthian Yacht Club|Seawanhaka Rule]] was used, and after 1937 smaller boats were desirable, and so the [[International Rule (sailing)|International Rule]] regained its popularity and became the standard. The 6, 8 and 12 Metre Classes were the most popular and the latter was used for the America's Cup until 1987, the last year the America's Cup was sailed in 12-meter yachts.

[[Naval architecture|Yacht designer]] [[Nathanael Herreshoff]] devised the rule in 1903. Herreshoff had designed winning America's Cup yachts which fully exploited the Seawanhaka rule, which was based only on a yacht's waterline length and sail area, to create narrow boats with long overhangs. This reached its peak with ''[[Reliance (yacht)|Reliance]]'', the defender of the 1903 America's Cup, which was described as a "racing freak", suitable only for certain conditions. This prompted Herreshoff to propose a rule which also took into account the displacement of the boat.<ref>[http://www.universalrule.com/index.php?page=3 universalrule.com ''History of the Universal Rule of Measurement'']</ref>

==Universal Rule formula==
Mathematically, the '''Universal Rule''' formula was: <math>R=\frac {0.2 \cdot L \cdot \sqrt{S}} {\sqrt[3]{D}}</math><ref>{{cite book|title=Elements of Yacht Design|author=Norman L. Skene|year=1904|publisher=The Rudder publishing company|url=http://books.google.com/books?id=V8TFHPwbgNgC&pg=PA146|page=146 | isbn=978-1-57409-134-2}}</ref>

Variables:
*'''L''' - Boat length
*'''S''' - Sail area
*'''D''' - Displacement
*'''R''' - Rating

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). Sailing craft are thus rated when their <math>R</math> rating falls within a certain range. J-Class boats, for example, are any single masted craft with an <math>R</math> between 65 and 76 feet. 

The listing for single mast boats, namely classes I through S.
*Class I: Rating = 76- 88 feet
*Class J: Rating = 65 - 76 feet
*Class K: Rating = 55 - 65 feet
*Class L: Rating = 46 - 55 feet
*Class M: Rating = 38 - 46 feet
*Class N: Rating = 31 - 38 feet
*Class P: Rating = 25 - 31 feet
*Class Q: Rating = 20 - 25 feet
*Class R: Rating = 17- 20 feet
*Class S: Rating = 0 - 17 feet

There were multi-mast classes too, running Class A to Class H.

<references/>

{{Yacht handicapping rules}}

[[Category:Sailing rules and handicapping]]