Racing different boats together
Sailors' passion for regattas is nothing new. Even before the advent of yachting and competitive sailing, fishermen, pilots and merchant sailors were striving to be the fastest, to earn a better living by selling their wares or services as effectively as possible. But in the interests of fairness, sailors were quick to set the rules of the game. This led to the emergence of the rules of measurement. Setting limits to certain dimensions, whether length, beam, weight or sail area, each country created its own restricted rule.
An international formula
But these rules were still often national, which posed a problem at the end of the 19th century, when regattas were opening up and bringing together sailors and boats from all over the world, notably during the Olympic Games or the great regattas of Cowes, Kiel and other yachting strongholds. To facilitate this task, the major yachting nations of the early 20th century got together in London in 1906 to form the International Measurement System, with Germany, the United States, Scandinavia, the United Kingdom and France.
A clever calculation of naval architecture
This time around, the gauge artisans don't just limit the parameters. They create a kind of magic formula based on 6 parameters:
- L:corrected length
- B: maximum beam
- G: the length of chain passing under the keel, corresponding to the length of a chain stretched from the live-edge to the bottom of the keel (2 on the diagram)
- d: the circumference difference, corresponding to the difference between the chain length and the actual planking length on a given cross-section. (1-2 on diagram)
- F: measured freeboard
- SA: measured sail area
The first formula from 1907 is
R = (L + B + 1/2G + 3d + 1/3âSA âeuros F) / 2
G and d allow us to take into account the differences in hull volume distributions between the very deep British ballasted corridors and the very wide American bearded flats of the time.
Arbitrarily, the committee has created 8 classes corresponding to R rating values, expressed in meters. There will thus be 5m JI, 6m JI, 7m JI, 8m JI, 10m JI, 12m JI, 15m JI, 19m J, and even the very rare 23 mJI.
Dimensionally, the calculation does indeed give meters, but this is not in fact a real parameter. Thus, an 8 mJI generally measures around 14 meters in hull length and between 9.50 and 9.75 meters at the waterline. Similarly, a 15 mJI approaches 28 meters in overall length.
A few revisions and some superb charts
The international gauge is far from perfect. It has evolved over time, with several versions, the latest dating from 1960 for the 2.4 mJI, 6 m JI, 8 mJI and 12 m JI, with only 4 parameters: R = (L + 2d - F + ?S) / 2.37 .
Meanwhile, the 8 mJI became an Olympic class, while the 12 mJI were the stars of the America's Cup for many years. Classic architectural jewels, many of these "metric" boats are the delight of enthusiasts at regattas in both the Mediterranean and the Atlantic.
