Matthew Sheahan

AMERICA’S CUP TEAMS ARE FINDING THEIR AC75S EVEN HARDER TO SAIL THAN EXPECTED... FOR A SURPRISING REASON

Anyone who has sailed a high performance boat with a large asymmetric kite will know how easy it is to look good when you can go where you want on the downwind leg. The problems start when someone else comes charging in and forces you to do something you were not ready for. So, when the America’s Cup World Series gets under way there will be plenty of people holding their breath, crossing their fingers – and possibly closing their eyes.

On the face of it, they have all learned how to get their boats to fly, but there is much more that the footage doesn’t show, at least that is what I’m being told.

From talk of bump starts, where boats have been towed up onto their foils and released, to rumours that some have yet to achieve a dry lap, it sounds like there is plenty still to master.

So being forced to tack or gybe when they don’t want to could cause a few issues. None has had to do it in anger yet because two-boat tuning is not allowed.

The first race could be a big moment on the road to the 36th America’s Cup and there’s a great deal of speculation about who will excel at what. The Italians are said to have the smallest foils and expectations are that they will be quick in the light. But there’s also talk that they’re not so hot through the corners.

Meanwhile, there’s confusion as to how the Kiwis are managing to go so fast in light conditions with the biggest foils in the fleet. Until they line up, no one really knows.

But among the fact, the fiction and the propaganda doing the rounds, my attention was focussed recently when talking to INEOS Team UK’S skipper Ben Ainslie about what it’s really like at the helm of these extraordinary beasts.

What has been clear from the start is that the axis these Cup boats heel around is aligned between the single T-foil rudder on the centreline and the main foil out to leeward. This means that when the boat heels it does so around a point that isn’t lined up fore and aft. So, when the boat heels to leeward the bow pitches up and when it rolls in to weather it pitches down.

Clearly this is going to play havoc with the angle of attack of the main foil and hence the amount of lift that it generates, especially when you are doing 35 knots upwind or 45 knots downwind.

The result is that crews need to perform the kind of balancing act that makes juggling flaming sticks on a unicycle look like child’s play. But according to Ainslie it’s even harder than that.

“The problem is that when the boat heels to leeward the righting moment reduces just at the time when you would normally expect it to increase on a conventional keel boat. Then, when the boat heels to windward the boat creates more righting moment just when you don’t want it, which pulls the masthead in further to windward.

“To recover, you have to spin around into the wind pretty quickly and re-set. It can be a violent manoeuvre to keep the boat upright, assuming, that is, you make it.

“The AC50 cats would cope with 20° of heel pretty easily when heading downwind and you could usually steer yourself back upright, but on the AC75S you’re sailing on a knife edge. It’s all about being precise on heel. If you’re slightly out you can wipe out really quickly.”

With such potential gains and losses it’s of little surprise to hear from others that the dialogue among the crew has changed as well. Apparently the talk is less of sail trim and far more about heel and balance.

But according to Ainslie, some things have got better for the helmsmen.

“On the F50s you did have quite a lot of turbulence on the rudder at times because it was in the flow of the main foil. On the AC75 the rudder is in a clear flow so it’s a lot smoother on the helm and much nicer to steer.”

For the crew providing the muscle power for these beasts, conditions have got tougher. Heads down and backsides up, they’re well below the level of the deck and have little, if any, view of the outside world. And while the crews see little of how their race is playing out, it sounds like we’ll see less of what is making their boat work, or not. So maybe it’s just as well the AC75S are twitchy, pitchy machines: it’ll give us something to judge them by. In fact, watching how much the mast heels or the bow pitches up and down when they have to avoid others may help make us all overnight experts.

‘On the AC75S you’re sailing on a knife edge’