The International 10-Metre Class is a construction class, meaning that the boats are not identical but are all designed to meet specific measurement formula, in this case the International Rule. At their heyday, Metre Classes were the most important group of international yacht racing classes, and they are still actively raced around the world. “10” is a product of the formula; 10mR boats are, on average, 16.5 meters long.

The 10mR was used as an Olympic Class during the 1912 and 1920 Olympics. The International Rule was set up in 1907 to replace earlier, simpler handicap system which were often local or at best, national, and often also fairly simple, producing extreme boats which were fast but lightly constructed and impractical.

Rule development

1907 Rule – used from 1907–1920

where

• L = waterline length (LWL)
• B = beam
• G = chain girth
• d = difference between girth and chain
• S = sail area
• F = freeboard

 

1919 Rule – used from 1920–1933

where

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

Information courtesy of Wikipedia.