Sailing professor Mark Orams: Breaking down the America's Cup 2021 designs

Emitates Team New Zealand sailing team aboard Te Aihe training on the Waitemata Harbour last month. Photopsort

COMMENT:

Advantage to New Zealand and Italy.

That's my reading of the America's Cup design battle, which could also be described as a drag race.

With American Magic skippered by Kiwi Dean Barker already in Auckland, joining Emirates Team New Zealand on the harbour, we already have the opportunity to compare the first versions of the AC75 yachts.

We have also seen video footage of the other two competitors, who are still trialling their first versions in the northern hemisphere.

So, what do we know so far?

We clearly see two different approaches to the design of the hull shapes for the new America's Cup class.

Team New Zealand launched their test boat Te Kahu in January. Photo / Photosport

American Magic's AC75 sailing on the Waitemata Harbour. Photo / Richard Gladwell

The ETNZ and the Luna Rossa Challenge design teams have gone with a "skiff" style hull shape – think a sleek fighter jet style of yacht. In contrast, the American Magic team and INEOS Team UK have gone with a larger wedge-shaped hull style. Visually they look very different, because they are very different.

What the design teams are attempting to create is a hull shape that balances two key attributes; stability and drag.

In order to hydrofoil successfully and consistently across a wide range of wind and sea conditions you need a stable platform. Touching down on the ocean surface, or even worse completely being stuck in the water, is slow. To be successful in this regatta you need 100% fly-time or as close to it as you can get (and certainly a higher percentage than your opponent). The key trade-off challenging the design teams is that more stability equals more drag, which slows the boat down.

American Magic's AC75 sailing on the Waitemata Harbour. Photo / Richard Gladwell

To understand the effect of drag, try putting your hand out of the window when you are driving along the motorway (keep the other on the steering wheel if you are driving please!).

The force you feel on your hand is drag, or more specifically aerodynamic drag. It's a strong force at 100kph and mimics the aerodynamic drag force these America's Cup yachts experience.

Now turn your hand from horizontal (palm down parallel to the road) to vertical (palm forwards with your hand at 90 degrees to the road). The force your hand is subject to increases dramatically because the area presented towards the air movement differs vastly from palm horizontal to vertical.

In simple terms, the designers are trying to present as small an area as possible to the direction of the wind.

At a basic level, more surface area means more drag. So Team UK looks to have the largest hull platform, then American Magic and then the Italian and New Zealand boats.

However, when you look at the designs of the larger hulls on the British and American boats the area they present to the wind coming across the bow over, under and around their structures is clearly designed to reduce this wind created drag. They are trying to have a stable, wide and large platform, but to present as little of this as possible to the wind.

Luna Rossa and ETNZ have a different approach. They have gone for a sleek and lower profile platform. This lower drag option is the way to go so long as there is enough stability to push the boats hard without risking the sort of splash-down or capsize which ETNZ have already suffered once.

The key question is; who has got this decision right in the battle for less drag with sufficient stability?

Each of the four competitors has already committed to the design of their second boat (you are allowed two in this America's Cup) and these four Version 2 boats are currently close to completion. The winner in the skiff-versus-wedge battle will emerge when these boats are revealed.

My bet is that the Brits and the American will change design tack to match the initial boats from ETNZ and Luna Rossa, who will in turn refine their first efforts.

If my prediction is correct, it means ETNZ and Luna Rossa are leading and the others are chasing in what might be called the 2021 America's Cup drag race.

Overall it has become a bit more of a guessing game, because the lead-up events were scrapped because of Covid-19.

But the word I hear is that the Kiwis and Italians are comfortable with their decisions, the Americans and Brits not so much.

Rumour has it that the British boat was smoked by the sleeker Italian design in the short time they were together on the same waters in Cagliari, Italy.

The race for this America's Cup began more than two years ago when key design decisions were being made. To my eye, ETNZ are leading right now, with Luna Rossa next best. The Americans and Brits are playing catch-up.

But as we learned from San Francisco in 2013, it is never over until it's over. Bring on the new boats and let's see what they've got.

***

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.