Written by Rebecca Hayter
10 March 2021
Here’s a weird thing about the AC75: smaller is often better, even for sails.
That’s because an AC75 flies in apparent winds of up to 60 knots. The faster it goes, the more drag it incurs, so the best way to go faster is not to have bigger sails but to lose drag.
This was a major problem for Ineos Team UK. Being sticky in the water, it needed more sail power to get airborne, but that bigger headsail incurred greater aero drag as the boat accelerated, lowering its average top speed.
Luna Rossa proved in the Prada Cup Final they had another gear: the question is whether that would be enough against the Kiwis, who have set the standard from the very start.
There have been rumours Emirates Team New Zealand’s Te Rehutai hit 57 knots in solo training runs, which if true, would be the fastest any of the AC75s have flown so far.
Emirates Team New Zealand has purposely left a few things late to trial, particularly in the sails department. They evaluated a new batwing mainsail, a lightweight Code Zero, and a mini jib prior to the main event.
If ETNZ has found a way to get airborne on smaller foils through superior trimming of its double-skinned mainsail, that will be a technical advantage. Simply put, a double-skinned mainsail actually comprises two mainsails (with separate luffs) set on the straight edge of a rotating D-section mast. Each mainsail has its own controls such as halyards, outhauls, cunninghams and mainsheet, so each can be trimmed independently of the other. By trimming the leeward mainsail differently from the windward mainsail, the trimmer can create the powerful depth required to lift the AC75 quickly on to the foils and then instantly flatten the sails so the depth doesn’t become drag at high speed.
Sir Ben Ainslie alluded to the highly evolving sail technology on display when an issue with Britannia’s hydraulics made it impossible to adjust the AC75’s cunningham during the race, necessitating a one-setting-fits-all approach that worked upwind but forced the boat into an unfavourable, high mode downwind.
“The cunningham is your power trigger for the mainsail, especially on a day like today [at the top of the wind limit],” he said.
Emirates Team New Zealand has consistently been ahead of rivals in the foil department. Team NZ has been using noticeably smaller T-shaped foils that should give them an advantage in moderate to heavy conditions. Luna Rossa’s larger Y-shaped foils have been working effectively in the lighter airs. Squeezing what they can out of the other end of the spectrum, respectively, will be crucial.
Each team can build six foils that can be modified – up to 20 percent of their mass may be altered – and they are able to build a greater number of flaps on the foils, which controls how much lift can be generated.
There’s no doubt that racing in the Prada Cup Round Robins, Semi-Finals and Finals has allowed the Italians to hone their high mode upwind, which worked so well against the Brits – a combination of constant trimming of sails, foils and helm. Both teams have evolved considerably since they last met in a knife-edge victory to the Kiwis in the America’s Cup World Series.
The Italians – and, significantly, Jimmy Spithill – now face the Kiwis as the America’s Cup challengers for the second time. There are various threads connecting the 2021 team to the Prada (Luna Rossa) challenge of 2000, which went down 5–0 to Team New Zealand, but they did so in inimitable style, earning the affection of many locals.
New Zealand’s recent record of three Cup wins since 1995, including the dominant display in 2017 in Bermuda is a factor in the contest, though all other things being equal, you can never discount the power of self-belief and a couple of fortuitous wind shifts.