ETNZ Update: if I were Jimmy

On average, ETNZ is between 1 and 2 knots faster than OTUSA. At average speeds of about 22 knots, that’s an increase of roughly 5% – 10%. In the old days of slow, heavy keel boats, that would be unthinkable. But with the high speeds and volatility of foiling catamarans it doesn’t seem like such a big ask. OTUSA are already faster in some instances.


Williwaw was an early sailing hydrofoiler. Owner/designer David Keiper sailed her across the Pacific and as far south as New Zealand in 1971. Photo source unknown.

OTUSA can select from two broad categories of modification: stuff that ETNZ is already doing, and stuff they’re not doing. The main kit that ETNZ has that OTUSA might put on the shopping list includes

  • Grunty foils
  • Pedals
  • Push-button wing control
  • Greater role distribution across crew members
  • Tidier windage profile among the crew
  • Windward heel

ETNZ’s large, light air foils seem to have a wider wind range than OTUSA. The Americans won’t be able to build whole new foils in 5 days. But they can modify the ones they’ve got, and they should have the data and the build capacity to make some tweaks. They could conceivably make up the majority of average speed difference right there.

It’d be pretty wild if OTUSA rock up to the next round with a full kit of pedal power. Pedals bring numerous advantages. In addition to power, they also facilitate a better windage package and different (usually better) role allocations.

But it’s hard to see them cracking the installation, running the on-water tests and then getting the crew familiar with the new tricks. But – hey – who knows what lies within the reach of rich dudes? They may have a full pedal kit just waiting to go in.

More power must have at least three direct impacts on speed: better fine tuning of the rig and foils; greater ability for big manoeuvres; and better use of crew energy.

I can think of two easier ways of getting more power. One is to get bigger stronger grinders. Olympic rowers, whatever. Although you’d think they’d already have the best they can get. I don’t know what the current class rules say about performance enhancing drugs.

The other way would be to generate electricity, rather than hydraulic pressure. This is in fact permitted under the class rules: a team is allowed to generate and store up to 60v of electricity. Is anyone already doing this? Why have no journalists asked about it? Maybe the batteries are heavier than the hydraulic accumulators. Maybe I have no idea. But you’d think …

Push button wing control – such as what ETNZ skipper/trimmer Glen Ashby uses – should be easily doable. I have no idea how these guys control different sections of the wing. But presumably having one ace trimmer in control of the whole thing via a little touch screen must be cool. With less physical work required it might keep the trimmer’s head clear to feed tactical info to the helm. I’d be surprised if this didn’t turn up on OTUSA on Sunday NZT.

Does it make the boat go faster? Pretty incremental, but conceivably. Remember, they’re only looking for 2 knots around the track. In some cases not even that much.

Separating the tasks of steering from foil control looks like it’s working for ETNZ, mostly. It’s possible that the pre-start nosedive against the British BAR resulted from foil trimmer Blair Tuke not anticipating such a rapid bear-away from pilot Peter Burling. But 99% of the time it just looks faster. It looks like Burling can concentrate on where to put the boat and Tuke can work on the hydrodynamics to get the boat there ASAP.

It could be that the Burling/Tuke relationship is the irreplicable x-factor in ETNZ’s package. They’ve completely dominated the high performance 49er class for the last 4 years, not losing a single regatta including the worlds and the Olympics (beating out Artemis’s Nathan Outteridge and Ian Jensen). They must have a deeply intimate knowledge of each other’s sailing style, and it would be interesting to know how much of that they can transpose from the highly physical 49er dinghy to the rather more mechanised AC boats.

The cycling thing looks like it gives the ETNZ crew a slightly higher but much smoother windage profile from the hunched backs of the front 4 crew, nose-to-butt like a peloton. And with upwind apparent windspeed of – say – 40 knots in a blow, windage is a significant factor.

Can OTUSA improve its windage profile without reconfiguring its grinding kit? Maybe. Probably not.

While all the teams sail around with bows down, ETNZ might also be digging in their windward rudder foils harder than the others, which slows the boat slightly because it inverts lift, rather than generates it, and in turn screws the windward bow down further.  Is it faster? Who knows? Windward heel is very popular among the foiling International Moth, and Burling was recently the world champ in that class, so maybe it’s the same thing.

Of course it’s impossible to avoid comparisons to the great upset of San Francisco. One day off, and OTUSA transformed their boat from one which was about the same speed as ETNZ to one that was faster upwind. They modified their foil control mechanism and from that point on, OTUSA became the first AC boat to reliably foil upwind, with a speed advantage on upwind legs measurable in whole knots.

Upwind speed seems to be more critical. Because upwind is slower than downwind, the boats spend more time in that mode. I’ve also noticed that most of the passing tends to happen in the top half of the upwind legs. Meanwhile in some races OTUSA had a downwind speed advantage over ETNZ, but were unable to convert that to a lead.

Whatever OTUSA pull off this time round, it won’t be a single transformation. But they can put together faster foils, and they can easily modify their wing adjustment. They’re already out on the water, so significant changes to the kit seems increasingly unlikely. Interestingly, ETNZ – celebrated by everyone as being the faster boat – is still in the shed undergoing modifications.

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