America’s Cup 2021: AUT’s sailing professor Mark Orams on Team New Zealand’s Te Rehutai

Professor Mark Orams has been taking a close look at all the America’s Cup boats on the water. Here’s his verdict on Team NZ’s Te Rehutai – and a challenger which is struggling to keep up.

Very impressive. That’s my verdict after seeing Te Rehutai sailing… or make that flying.

I also believe Team New Zealand have come up with a breakthrough design feature which leaves the challengers in their wake. And one challenger in particular is in very big design trouble.

TNZ have clearly come up with very smart design features. It is the integration of the ideas that is most striking. It’s a complete package beyond anything the challengers have come up with.

The flared concave bow shape of Te Rehutai made immediate sense to me, as did the keel/bustle running the length of the hull.

What was less clear (to me anyway) was the wisdom of having an extremely wide stern and box-like form in the back third of the hull.

Such a large surface area can be “sticky” in the water, and increased surface area usually leads to more drag in the air when flying. However, when you watch Te Rehutai in and above the water, you can see how the wide, flat and deep design works.

The volume creates buoyancy and as soon as the sails fill and start to generate some power, the hull leans with the wide stern section exiting the water. As she lifts onto the foils, there is synergy between the aerodynamics and mainsail.

And you only just see the top of the sailors’ helmets poking out of the cockpit trenches. Everything else is out of the wind. Sweet.

Speculation around TNZ using a helmsman on each side, like Luna Rossa, appears to be incorrect.

The choreography on Te Rehutai looks similar to Bermuda in 2017 where Glenn Ashby, Blair Tuke and Peter Burling change sides before and after turning the boat. However, the poor “grunt-machine” grinders stay put as the soldiers in the trenches and keep on turning the pedestals.

A key difference between the teams is the main foil designs. TNZ have very high aspect (long, slim and straight) foils with small winglets at the tips. The other teams appear to have much wider foils set at a downward angle towards the tip. These configurations are more stable but slower due to the extra drag they create.

Furthermore, TNZ have made a significant breakthrough by putting the weight needed for stability into especially designed extensions at the end of their foil arms. This allows them to have their slim-line foil wings which make all the other teams’ foils look quite basic in comparison.

The team struggling most in this area is INEOS Team UK. Despite their radical hull design, they look in trouble to me. Their foils are wide, angular and draggy. Foils take two to three months to design and build meaning they are stuck with ones that are off the pace, unless they already have something special in the shed.

I also love the way Burling and the team are sailing Te Rehutai. Straight out of the box they revealed a new technique when flying on the foils upwind.

This involves immediately canting (leaning) their foil wings so the leeward wing tip just pierces the water surface. This helps reduce sideways slipping and provides lateral resistance. In simple terms it allows Burling and co. to keep the accelerator pedal down thus increasing straight-line speed.

It’s also noticeable that TNZ are turning their boat more quickly and through a tighter arc than the challengers. This is reminiscent of their impressive manoeuvres in Bermuda, which were a major advantage. Straight-line speed is important, but the ability to turn quickly and stay flying will be critical, especially in the pre-start.

Practice racing starts next week. All the teams will be amped.

Don’t expect a lot of pre-start fireworks – it’s too dangerous. The most powerful move will be one that forces an opponent into a corner of the start box requiring them to make a turn which drops them off their foils.

The bottom left “corner of death”, where the boats will have no runway to take off again, must be avoided.

Hitting the start line as close to the start gun as possible, on the foils and at full speed, will be vital. Getting it wrong will concede hundreds of metres.

This America’s Cup will involve a different style of racing minus the old school pre-start drama. It will be all about minimising risks and ensuring a clean, flying start.

Bring on December 17.

Professor Mark Orams is the Dean of the Graduate Research School at Auckland University of Technology and is a former member of Team New Zealand. He was also part of Sir Peter Blake’s winning Whitbread around the world yacht race crew aboard Steinlager 2.

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