In describing the luff shape of Doyle Sails’ new cable-less Code Zero, the designers use a lens analogy – which neatly illustrates the smooth curve that projects forward but gives no hint what it actually achieves. That subtle bulge represents a significant performance gain and an elegant solution to an issue that has troubled these asymmetrical sails ever since increasing boat speeds started dragging apparent wind further and further forward to the point where offwind progress was achieved with upwind trim.
Pictured: the Maxi72 Momo on the way to becoming 2017 world champion at the Maxi Worlds in Porto Cervo. The three individual luff ‘lens’ groups are visible on this Code Zero – the combined effect being to allow the luff profile to project significantly to weather with no blowback of surplus material.
As is often the case, class and rating rules often lagged behind the pace of technical development, leaving sailmakers and competitors to adopt clumsy work-arounds to extract the available performance within outdated regulations.
Almost from the time that asymmetrical spinnakers became mainstream, the name of the game has been to design flatter and flatter sails – until they came up hard against limits imposed by the rating rules.
Under IRC, for example, the definition of a spinnaker demands that the mid-girth measurement is at least 75 per cent of the foot length. Other offshore racing classes have similar constraints. The challenge was to achieve a sail with the area of a spinnaker and able to be used for heavy-air running, yet flat enough to operate like a masthead genoa at relatively tight angles in lighter airs.