Wings, the Next Generation
by Kimball Livingston on 2 Dec 2011
Wanna have some fun? Set Paul Cayard loose on the subject of America's Cup 34, some re-imagined and surprising wing-control mechanisms, and the terrors of San Francisco Bay in full cry. The custom AC72 catamarans of 2013, he says, will be 30 percent more powerful but 'much less stable' than the AC45s that sailed three events this year on the America's Cup World Series circuit.
The slim lightweight design Cogito, the 1996 Little America’s Cup winner © Richard Gladwell http://www.richardgladwell.com
And occasionally failed to maintain verticality.
Cayard's home waters, where the Cup will be sailed, are known to be a windy spot, and when the ebb tide works against the seabreeze—one sixth of all the water in San Francisco Bay goes out, and in, twice a day—then she be lumpy, mon. Sea state, even more than wind strength, is something to fear once the breeze is up, funneling through the Golden Gate and peaking on many days at 18-22 knots. Unless it peaks at 30, and shucks, that's just home for the home folks. But what does it mean to racing an AC72 with 38 hydraulic cylinders in the wing?
Until the first AC72s are launched in July, 2012, it's all theory, but, 'If you're making 25 knots upwind and 40 knots downwind, tacking on someone and gassing them just isn't happening,' Cayard says. 'In seriously-overpowered boats, the match will be about who can actually get the boat around the course and figure out how to avoid that extra gybe that costs you maybe 20 seconds, maybe 250 meters.'
As CEO of the Swedish challenger, Artemis Racing, Cayard is not shy about telling you that his Challenger of Record team has gone its own course in engineering an AC72 wing. The box rule governing the AC72 is one big sandbox, so the engineers get to play.
Oracle Racing Team Coordinator Ian Burns explains: 'I was involved in writing the rule for the AC72s, and when we addressed the wing, we started with a complicated rule, to limit what a designer could do. We added more and more pieces as we thought of more and more outcomes, and we came to a point where it was so complicated—and it was still going to be hard to control, because the more rules you write the more loopholes you create – that we reverted to a simple principle. Limit the area very accurately, and make it a game of efficiency.'
The Artemis approach to efficiency, Cayard says, uses a three-element wing. No surprise. Any wing is much more efficient than a mast and soft sail—for many reasons, not the least of which is that mid-leech tension becomes a non-issue—and C Class catamarans long ago demonstrated that three elements, two slots, are faster than two elements, one slot. I expect every AC72 to have a three-element wing.
Unless, or until, someone develops a fully-warpable single-element wing, but that's for another day . . .
In C cats, the middle element has been narrow, which probably is a portent for AC72 wings, but what do I know? There's never before been as much money or as much research thrown at the problem as now.
But when you scale up to a wing 130 feet tall, how do you control the beast? The first Artemis wing is under construction in a special facility in Valencia, Spain, Cayard says, and to control the moving parts in that wing, 'We have 38 hydraulic cylinders. We want to avoid running hydraulic piping to each of them, because that would be heavy, so we have electrovalves embedded in the wing to actuate the hydraulics. But if you had two wires, positive and negative, running to each electrovalve, your wing would look like a PG&E substation, and that's heavy too, so we use a CAN-bus [controlled area network] with far fewer wires. Still, it's incredibly complex.
'We wind up with lot of hydraulics,' Cayard says, 'and the America's Cup rules don't allow stored power, so two of our eleven guys—we think, two—will be grinding a primary winch all the race long. Not to trim, but to maintain pressure in the hydraulic tank so that any time someone wants to open a hydraulic valve to trim the wing, there will be pressure to make that happen.'
Nathaniel Herreshoff (with Cayard, one of the first 15 people inducted into the National Sailing Hall of Fame) built a catamaran called Amaryllis in 1876, but it was too fast, too different, for its time. There is no way that Nathaniel Herreshoff could have foreseen an AC72, but he was the type of guy who would have been thoroughly intrigued.
I'm guessing the people who wrote the AC72 rule didn't foresee the Artemis configuration of wing controls, either, but I didn't get invited to that meeting so I really don't know. When I asked Cayard about the lineup, he allowed as how the competition's hydraulics are 'probably a bit different.'
The Wing, the Hull, the Hull, the Wing
Cayard figures the 'boat' is a four-month build at $4-5 million (the airfoil-shaped crossbeams themselves taking four months) and then 'The wing is about the same again, but it's a six-month endeavor.'
And how will this Artemis wing fit into the fleet to be?
The fleet of which we know almost nothing . . .
'Once you have a setup like ours you could easily autopilot the thing,' Cayard says, 'but that's not legal. You must manually control the wing, with no stored power. With our guys grinding to maintain hydraulic pressure, someone else on the boat can push a button and send an electric current to a switch that will open a valve to let hydraulic fluid flow to shape the wing.
'It's a fine line. They're still refining those rules.'
Footnote: The one-design AC45s now on hiatus until America's Cup World Series racing resumes in April in Naples, Italy, were purposely kept simple because the game needed boats on the water, and the engineers needed to get it right the first time. Thus the two-element wing. Thus the straight daggerboards. The design team got it right, and the boat is a winner.
But no one is going to bring that package, upsized, to the gunfight of 2013.
I'm just telling you.