“The International Rule” ( Metre Rule )

© K. Urtz 2010

chain girth skin girth
L = waterline length (LWL)
d = difference between skin girth and chain girth
S = sail area
F = freeboard ( area between the waterline and a
specified deck edge )
2,37 = a mathematical constant

The International Rule differs between classes, the smallest called 5-m and the biggest has a 23-m
rating. Best known is probably the 12-Metre Class sailing in 8 America’s Cups from 1958 to 1987.
They followed as far less expensive yachts the impressing and costly J-Class of the 30’s . Their
construction has been stopped by the Second World War. 12-m does not mean the length of a yacht
in metres. The “m” is the term for a mathematical equitation only (a recommendation to use metric
units.). The 12 Metres of the AC have a LWL of about 14 m, a total length of about 20 m and
displacements of around 20 tons. The formula keeps a balance between the below parameters. A
change of one of the figures requires the change of the others - in order not to exceed the number
12. The rule has been changed three times, the last version has following rule

Freeboard

“The International Rule” ( Metre Rule )
Around 1900 the European Yacht Clubs were looking for an
international rating rule to assure that a yacht can race in the
same class and under the same specifications in every
country. Initiated by the British YRA (Yacht Racing
Association ) and created in several international conferences
( final ones 1906 in London and Berlin ) the International
Rule (Metre Rule ) has been ratified 1907 in Paris. On this
occasion the international delegates formed the IYRU (
International Yacht Racing Union ) now replaced by the ISAF (
International Sailing Federation). As rating bodies the Lloyd’s
Register (GB) the German Lloyd (D) and the Bureau Veritas
(F) have been applied. At that time the USA has sent
observers but continued with the Universal Rule based on a
formula of N.Herreshoff.

AMERICA’S CUP HISTORY 1983 - 2013