Here’s the second part of the interview Sailing World editor Dave Reed had with Emirates Team New Zealand technical director Nich Holroyd (pictureed right). The interview was first published in the October issue of sailing World magazine.
There’s a lot of boat to cross for the manoeuvres; how does everyone get up on that hull quickly?
One guy leaves the weather side early to load up a sheet winch and set up the boards. Then the majority of the crew crosses the boat as it’s going head to wind. You leave a couple guys behind to get the board down and then bring them across. We’re looking more to have weight on the high side out of the tack—you need that full power to sheet on the wing and get the acceleration going because your boat speed deltas between the bottom of the tack and getting going again are vast. Getting the guys up to the high side early to have stability is very important.
How about the helmsman getting from wheel to wheel?
There’s a triple act between Ray [Davies], Dean [Barker], and Glen [Ashby]. Someone’s taking the wheel off Dean, and he’s set up to take the wheel out of the tack. The boats are actually pretty efficient through the tack, unlike most multihulls, because the wing drag is low compared to soft-sail cats.
It appears your rig is farther aft than that of Oracle’s. What’s the tradeoff?
Again, it comes down to structure, and in this case, how much forestay tension you can achieve within the structure. A lot of forestay tension means a lot of stretch in the forestays, backstays, and under-rigging, which means a lot of work in terms of grinder input. The boards are highly loaded, and going through those manoeuvres is about keeping wing controls relatively simple. If you have too many controls to get the wing shape to where you want it to be, you’re likely never going to get there.
Is it possible to make the boats simple?
With the AC45s, the courses are pretty small. If you speed it up by 25 per cent, it gets really, really small. It will take about 2 minutes to cross the box from one side to the other, so the manoeuvres come thick and fast, and then you add extra manoeuvres as you interact with the competition. That’s where the huge amount of resources will go in the next few months. The hydraulic systems are a big step up, and getting those tuned so the right controls fall into hand during each manoeuvre will take a lot of time. The final thing is reliability. Everything is built at such tight weight constraints, so you can’t throw weight at things to make them reliable. It will come from using them and measuring the loads and carefully paring back anything you overdesigned. It’s all about measuring everything that goes on and off the boat: how long the running rigging has been on the boat, how many tacks and jibes a given piece of rigging has been through, and taking it and breaking it on a bench to understand if it’s degrading over time.
How do you effectively alter the wing shape from top to bottom without overcomplicating it?
We need hydraulics in the wing, no doubt about it. The question is how to distribute things around the wing—whether you do that by introducing more hydraulic cylinders farther up, or taking a cable off a cylinder at the bottom and distributing the forces around the wing that way. Quadrants and cables control all the upper control surfaces, so we can do some clever stuff at the bottom. It’ll be interesting to see if anyone else thinks they can get finer control of individual panels and surfaces by going more heavily hydraulic. I read that Artemis has 30-something hydraulic rams in their wing, which implies they’re controlling individual surfaces with rams all over the wing. That’s a complicated system for sure.
What about the foils, and the concept of foiling?
The game is about generating vertical lift off the foils, which is reasonably quick, but it does lead to serious control issues when you get it wrong. It’s quick because it reduces wetted surface area, but the challenge is achieving controllable levels of lift. It’s easy to wheel stand these boats, or fall off the foils with a severe crash. You might survive that crash, but the average speed won’t be good. It’s all about finding and maintaining a high average speed. The boats need a certain amount of foil lift to even be able to bear away, and that ability also comes down to hull volume and freeboard decisions. It’s a complicated part of the puzzle. It will be an interesting part of this competition.
How do you monitor everything that’s happening with the boat, structurally?
We use fibre-optic sensors that are embedded into the composite structure to measure loads. There are about 50 in the platform, another 25 in the wing, six in each daggerboard, and a couple in each rudder. In every hydraulic function, you’re monitoring pressure, and in the winches you’re measuring loads. You’re measuring very accurately the pitch, roll, and heel, and all the various attitudes and speeds of the boat. Boat speed measurement is a tough one because sometimes there’s not a lot of boat in the water, and it’s hard to find anywhere on the hull that has good, clean, consistent flow. Wind direction, too, is actually very difficult on these boats because the apparent wind angles are so fine downwind that downwind prediction is very tough. There are a lot of technical issues to solve in that area alone.
What realistic speeds can we expect?
You’re going to see VMGs over 30 knots at the top end downwind. What will surprise people is that the performance delta upwind is bigger than the deltas downwind. The pace upwind will certainly be in the 18- to 20-knot range a lot of the time. The guys are already saying there’s no sensation of speed on the boat because everything feels smooth and controlled.