# 9 Metre (keelboat)

Current Specifications
LOA 18 m (59 ft)
Infobox last updated: 19-APR-2010
Former Olympic Class

The International Nine 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 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. "Nine" in class name does not, somewhat confusingly, refer to length of the boat, but product of the formula; 9mR boats are, on average, 18 meters long.

## History

The 9mR was used as an Olympic Class during the 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. The rule changes several times in history. About 50 boats were ever build.

## Rule development

### 1907 Rule

Used from 1907–1920

$9.000 \mbox{ metres} = \frac{L + B + 1/3G +3d + 1/3\sqrt{S} - F}{2}$ where

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

## Olympic results

No competitors did enter the Olympics in the 9 Metre.