Evolutions and revolutions
The advances in the Imoca fleet in the current Vendée Globe cycle have been extraordinary – from breathtakingly (at the time) fast foiled designs with a mix of Dali and DSS appendages in 2016 to designs capable of long bursts of full flight even without any rudder elevators. Then talk to the designers and teams and it is clear we have barely touched the surface in terms of foil development. Come the race and of course the result will be down to reliability and the experience of the skipper as much as outright speed; however, by two months before the race start there were clear signs that one boat may well have the legs on the 2020 fleet in pure performance terms – and while probably incidental to the race outcome such a distinct step-up in potential has flagged up another gapping upwards in speed when the next-generation designs hit the water. François Chevalier looks at how performance has advanced so far in the relatively short period since the Imoca class came of age
40 SEAHORSE
The shapes of sailboats have very different origins. They are most often driven by navigation conditions, their purpose or ultimate destination and the construction techniques of the time. However, the main factor in the design of racing yachts remains a rule defining time allowance, in other words, the prevailing handicap rule. Between 1860 and 1890 the American
school favouring flat underwater lines – derived from east coast fishing boats – was pitched against the British tradition of narrow hulls, which later spawned width being taxed. What ensued was a compro- mise, which can be described as an open V-shape, and this approach dominated the three America’s Cups that took place between 1885 and 1887. However, a few years later, beginning in
1891, there was effectively a mini design revolution with wetted surface area sud- denly given a higher billing, prompting a new generation of hulls with less wetted area leading to the low-drag, rounded canoe shapes that would become the norm for the next 10 years or so. In fact, at the turn of the century many racing yachts were still being designed with speed as the primary goal, with little or no thought given to the handicaps of the day. But then in 1903 a new rating rule – the
Universal Gauge – entered the frame in the US. This would ultimately turn everything
on its head. First in the US and later on a much wider scale when this rule evolved into the International Gauge, brought into operation in 1906, suddenly slippery canoe shapes were no longer competitive in handicap competitions and designers and customers ignored the rating cost of speed-related design factors at their peril. The more familiar post-war offshore
rules, first the RORC rule in the 1950s and then the IOR, in turn continued the same philosophy of rating sharing at least equal (sometimes higher) status with outright speed in racing yacht design. With the RORC/IOR system the new culprit was stability and a great deal of design effort went into seeking ways to minimise mea- sured stability for rating purposes; the result was that for its length a competitive racing yacht of the time was significantly slower through the water than would have been possible without such constraints. The effect was that within the frame-
work of RORC/IOR radical progress in yacht design all but ceased. It is not until the appearance of the solo races, devoid of any rating rules, that hull forms were freed once again from 60 years of restrictions. The Transat (1960), Transpac (1969),
Mini Transat (1977), Route du Rhum (1978), BOC Challenge (1982) and then the Vendée Globe (1989) will be the cradle for the renewal of naval architecture.
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