ISMA News - Association Suisse 6mJI

ISMA News International 6mJI Association Bulletin 1/2004
The metric rule
We have the chance to reprint a very interesting report about the metric rule development, which has been edited by our
Chief Measurer, Guy-Roland Perrin, and published in French and UK Magazines before.
The metric rule
To write about the meter class measurement rule makes me feel a little pretentious. Of course these formulas, these
measurement instructions are familiar to me, but before starting these lines I felt necessary to go back to the basic, to go
back to the rule and the literature left back by several historians, naval architects from the beginning of the century or
even specialist of the meter rule such as the former IYRU technical chief, Tony Watts. The all story is almost a story of
mad, a continuous dispute between Great-Britain, France and USA.
Everything started at the end of the last century. Great Britain was still mastering … and ruling the sailing as a sport. In
the middle of the IX X century winning a yacht race was essentially due to the size of the yacht and the amount of sail she
was able to carry… this was not really what one could name “fair competition”. Several Yacht Clubs, you know what I
mean, these nice places on the see shore populated only by gentlemen, decided to discuss the feasibility of a rating rule
allowing yacht of different size to compete together in a fair competition. This was the beginning of the trouble.
At that period there was only one rule, a single denominator, across the different nations: the rule used by the custom to
evaluate the volume of goods arriving by sea in a country.
Tonnage =
L x B x H
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L= Longueur de coque
B= Bau maximum
H= Profondeur de coque
The willingness to compete together for the yachtsmen (the gentlemen from the club!), as well as for the architects and
the engineers grows, and step by step the key elements characterising a sailing yacht have been included in the various
formulas. The length, the beam, the draught were the first components of the rule, ignoring totally the sail area. If the
desire to reach a single formula was shared across the oceans, the rules, even (specially!) across the Channel were
different, each of them giving advantages to the local architects. Great Britain was well known for narrow and deep yacht
(the beam , stability of hull shape, was heavily penalised), when USA was in favour of the sandbaggers, with large beam,
almost no draught and including moving ballast (that often was not anymore on the boat at the arrival of the race!)
Huge bowsprit and boom, not to mention the mast, fit these yachts, allowing them to carry impressive and free (from a
rule perspective) sail area.
That “error” led the gentlemen of the yachting of the end of the past century to think again to their respective rules, and
between 1886 and 1890 to include a factor proportional to the sail area.
In no time the architects react, and the displacement being absent of these formulas, they designed boats as light as
possible (life expectancy was about a season).
With these several experiences the ground was ready for the future linear meter rule, but the consensus among the
international yachtsmen was far to be reached, and competing (and great) classes such as the “sonderklasse” and the
6.5m were trying desperately to impose themselves. Still today one may ask itself what has allowed the meter rule to
impose itself and last so long.
Jauge linéaire =
L + B + 0.75 G + 0.5 SQR(SA)
L = Longueur de flottaison "dynamique"
B = Bau maximum
G = Périmètre de la carêne à "mid-ship"
SQR (SA) = racine carrée de la surface vélique
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