Opposite: it is September 1993 and the then Whitbread RTW race is taking its first big leap into the future after 20 years of evolving IOR design, race winner Ross Field’s Whitbread 60 Yamaha 2 leading the last ever IOR maxis out of the Solent at the start of Leg 1. Yamaha would return to the Solent only 10 hours behind Grant Dalton’s winning maxi… overall. The team that should have (easily) won that race before being dismasted was Chris Dickson’s W60 Tokio (above), seen making the most of the final blast to the finish
good for safety – AC72 daggerboard tips all point inboard. This configuration was further tightened
with the ‘box’ rule for the AC50 dagger- boards, although this permits boards to exceed BMax to a limited degree above deck. The flying cats of the America’s Cup in San Francisco spawned a number of smaller new one-designs or retrofitted boats, from the GC32 and Flying Phantom to the new flying Nacra 17 Olympic catamaran, all featuring AC72/50-style daggerboards. A tour of the boatpark at Weymouth
Speed Week or Foiling Week in Garda shows that there are plenty of other configurations that will readily get a boat flying, for exam- ple L-foils with the tips pointing outboard, only they aren’t the fashion. But, in particu- lar, they haven’t benefited from the gazillions spent on R&D covering every aspect that the foils created in Cup-land have been given. Similarly in the monohull world foil
development has been driven by the Imoca 60s, but also by Dynamic Stability Systems. DSS foils, when they were first unveiled more than a decade ago, were designed principally to provide lift to leeward in a pleasing Newtonian kind of way: on a DSS-equipped boat an increase in wind is translated more efficiently into extra speed as the faster the boat goes the more lift and righting moment the DSS foil generate (hence the ‘D’ in DSS). So, unlike a conven- tional keelboat, a DSS yacht, thanks to its foil, gains stability the faster it goes.
DSS foils have since evolved and are
now capable of getting boats fully airborne or at least airborne to a much greater degree than witnessed to date in the Imoca 60 fleet. They are used on the award-win- ning Hugh Welbourn-designed Quant 23 scow and the 747 SEAir Mini (issue 448). While DSS foils were born without
consideration of rules (although they have since caused the RORC rating office much head-scratching), this was not the case for Imoca 60 foils. Imoca foils aren’t limited by beam
restrictions (in fact, BMax of 5.85m for the hull was only introduced prior to the last race), but Imoca 60s are limited to a maxi- mum of ‘only’ five appendages. Imoca 60s have twin rudders to reduce
drag and provide neutral helm to reduce autopilot power consumption; with a cant- ing keel it is then necessary to have some- thing in the water to prevent leeway and while a few early boats had a single central daggerboard more usually twin asymmetric daggerboards are fitted. Early daggerboards on canting-keel
Imoca 60s were typically toed out, like the twin rudders, with the aim of being vertical when heeled. The 2004 Farr-designed Virbac-Paprec was fitted with boards that were vertical in the boat and inclined when heeled, providing some vertical lift. By the 2012 Vendée Globe this had developed on Banque Populaire and François Gabart’s race winner Macif to boards that were
‘toed in’ and mounted well outboard, penetrating the deck close to the gunwale and developing even more vertical lift. But the foils fitted to the last-generation
Imoca 60s represented a quantum leap in vertical lift, causing a dramatic reduction in wetted surface area and, occasionally in stronger winds, boats to get airborne. However, a downside of the new foils
(apart from mooring them side-to) is that the prevention of leeway has become sec- ondary. According to skipper Séb Josse, the area of Edmond de Rothschild’s Dali foils used to counter leeway is 1.8m2
, compared to around 4m2 for a conventional dagger-
board. Not surprisingly, last-generation Imoca 60s are not weapons upwind. The Imoca 60 five-appendage limit also
hasn’t helped. While going for a one-design keel and mast package improved reliability, it didn’t reduce costs; for the larger teams building new boats budgets increased this time by around 30 per cent (a foiling Imoca 60 will leave you little or no change out of 5 million euros). A suggested solution was to change the
Imoca 60 rule to permit seven boards, including two pairs of daggerboards. This would solve upwind performance as one set of boards could be dedicated to prevent- ing leeway leaving the other to provide vertical lift. This would also reduce costs as two pairs of straight (or straighter) dagger- boards will cost less than constructing a single pair of Dali boards with a giant,
SEAHORSE 49
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PPL
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