SANITY CHECK
Yachting World|January 2021
THE GRAVITY-DEFYING AC75S WILL RACE ONE ANOTHER FOR THE FIRST TIME IN DECEMBER. MATT SHEAHAN CHECKS OUT THE FOUR DESIGNS
MATT SHEAHAN

As each of the new AC75s were wheeled out into the open for the first time, amid the celebration and champagne spraying, each team will have been keenly aware that this was it. Barring disasters, these were the boats that would face each other on the start line. After more than two years of planning, scheming, data-crunching, building, testing and training, this was their shot at the America’s Cup.

The pressure has been made even greater by the lack of any opportunity to compare themselves against the other teams, after the two 2020 AC World Series events in Sardinia and Portsmouth fell victim to the pandemic. Had they gone ahead, these regattas would have provided valuable intelligence about the relative performance differences across the fleet, and some clues about which design approach was pursuing the right path. Much of that knowledge would have been gained while there was still time to do something about it. Now there is none.

The result is that, despite all the ‘competitive reconnaissance’ – or what you and I would call spying – that every team has been engaged in since the 36th Cup cycle started, rarely has so little been known by the competitors about their opponents.

But this hasn’t stopped others from speculating. Before the launches, there was a school of thought that, despite some wildly different design approaches for the first boats, the second AC75s might show the four designers’ thinking had shifted towards a similar corner of the rule. But when the new boats were unveiled it was clear that such a consensus did not exist.

Ahead of their first races over 17-20 December, we take a close-up look at the four very diverse AC75s:

INEOS TEAM UK

THE BOAT BRITANNIA II

There’s no disputing the British boat is the most extreme of the challengers. The most noticeable feature is her chunky, aggressive skeg that starts like a battering ram at the plumb bow and runs down the centreline, stopping just in front of the rudder.

The broad purpose of a long skeg to maintain an aerodynamic seal between the hull and the water’s surface as the boat begins to fly is becoming increasingly clear, but little is yet known about why chief designer Nick Holroyd and the British team have gone for such a chunky configuration.

“It has benefits through the take off and aerodynamically when the boat’s flying as well,” Holroyd said of the ‘bustle’, as he referred to it.

Interestingly this deep, box section affair doesn’t appear to be aero- or hydro-dynamically sympathetic until you look from under the boat. From this angle the bulge in the box section as it travels aft suggests that the skeg is generating hydrodynamic lift somewhere around midway down its length. This would imply that the longitudinal position of maximum lift would be somewhere near the foils. Perhaps, when the boat is heeled to weather and getting ready to take off, the water flow on the windward side reduces leeway by sucking the boat up to windward which helps to get the leeward foil working?

There’s also a question whether the box type section of the skeg provides a lighter structural beam to make the hull stiffer fore and aft. If this is the case it could be that space has been freed up inside for systems and/or that it means the weight budget for structure can be used in other areas.

Another interesting feature is the distortion in the hull shape aft which appears to be a way of reducing the waterline beam and therefore wetted surface area quickly as the boat lifts, which in turn will provide a step change in acceleration – a performance aspect that will doubtless prove critical on a race course that has plenty of corners and boundaries to accelerate away from.

“Slow speed manoeuvring is quite difficult and the initial stage of acceleration is tricky,” said team pilot Leigh McMillan, the crew member responsible for flight. “[But] the acceleration through the midrange is going to be a huge step forward.”

Whichever way you look at it, Britannia II is a radical shape. “We’ve pushed bloody hard and left nothing on the table,” said skipper Ben Ainslie.

“The whole team has shared the philosophy that we’ve got to go for it.”

THE F1 FACTOR

A tie-up between an America’s Cup and Formula 1 team sounds great in principle, bringing together engineers and designers at the leading edge in two massively technical sports, writes Ed Gorman. But in reality it’s difficult to make such a collaboration work because the differences tend to outweigh the points of cross-over.

However, the word from inside Ben Ainslie’s team is that INEOS Team UK’s relationship with Mercedes AMG Petronas Formula 1 has been a major influence. The Mercedes outfit based at Brackley in Northamptonshire has dominated Formula 1 for years, helping Lewis Hamilton to six of his seven world titles.

To start with the two sides were somewhat wary of each other. “You could see them sizing us up,” remembers Grant Simmer, CEO of INEOS Team UK. “I mean there they are, multiple world champions, and then they are talking to these guys in the sailing team who operate on a much, much smaller scale than them.”

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