Emirates Team New Zealand launches radical Cup Defender

America’s Cup: Emirates Team New Zealand launches radical Cup Defender

by Richard Gladwell / Sail-World.com / nz Nov 19 02:50 PST
November 19, 2020

The America’s Cup champions revealed their AC75 Version 2 today at the team’s base in Auckland’s Viaduct Harbor.

Christened Te Rehutai by Lady Margaret Tindall, the radical 75-foot foiling monohull is a design departure from most experts’ expectations, which was a development of her team’s first AC75, Te Aihe, launched in September. 2019.

That ship never sailed in a race, and Te Rehutai was designed based on performance analysis of Te Aihe data, and using equipment design and navigation simulators. That process was carried out using the team’s 12-meter test boat, Te Kahu, while Version 1 AC75 shipped to Europe in mid-January. The AC75 program rebooted with Te Aihe in early June.

“It is a fundamental mistake to think that you are designing a boat,” says the team’s executive director, Grant Dalton. “You have to see the ship as an object, a flying object that leaves the least possible footprint on the planet, like a racing car.”

Dalton’s design philosophy explains much of the rationale for the AC75, which would appear to be an outlier at first glance, but when broken down into multiple elements the synergy of the design becomes quite clear.

The ship largely borrows aerodynamic thinking from F1, perhaps not surprising given Chief Designer Dan Bernasconi’s Ph.D. in mathematical modeling and aerodynamics, and six years at McLaren Formula 1 over six years, leading its modeling team. of vehicles, before swapping fast cars for fast boats.

The hull design was signed in October 2019, about three months before the Challengers, and with only two months sailing in Te Aihe.

However, it is the decision to run a 12-meter-long test boat, the maximum allowed under the Protocol governing the event, that has kept the Kiwi test program running near full speed through the COVID19 outages. .

Like all boats, the Kiwi V2 AC75 has a bow, a center and a stern.

By breaking down those components, the bow is most notable for its pronounced flare, along with a deck that rounds toward the bow of the boat. All of this provides plenty of buoyancy in the event of a nosedive and helps keep the crew dry and the water out of the pits.

The head of design at ETNZ explains that bow design thinking is based on “accelerations and touchdowns too, when you come off the fins at low wind speed or when something does not come out perfectly in a maneuver.”

In that sense, the new AC75 should be a very forgiving boat, which makes handling easier and encourages the crew to try harder with less risk of the consequences of a small mistake.

“It’s about trying to minimize the amount of hull in the water,” Bernasconi explains.

Returning to the center of the ship, there are the high sides that were first seen in the first British AC75. These contain the crew pits and are deep with only the head and shoulders of a fairly tall crew member sticking out. That reduces wind resistance and again protects the crew when sailing in apparent high winds, speeds of around 60 knots, and in spray.

The center of the ship is completely clean and, like the first British ship, the sails will flow out on the deck, below the level of the gunwale. Between the crew wells on either side, the deck is clean and provides a channel to clean the water from the deck. The raised center in Te Aihe’s cabin is gone.

The stern of the boat has a John Spencer style hard back whose chief designer, Dan Bernasconi, explains that it is to give the hull greater shape stability and achieve the minimum roll moment required by the AC75 class rule. Beneath the body of the canoe, the boat has an almost flat bottom, with a small skeg in the center line, quite similar to the aft of the American Magic, and like the US boat. bow.

The hull volume is brought directly to the aft end of the AC75, with relatively straight spines from the full beam, around the point where the blade arms intersect the hull.

Put those three elements (bow, middle and stern back together to form a hull) and the unusual shape of the Version 2 AC75 starts to make sense in the design.

Explaining the different design approaches taken by the four America’s Cup teams, Bernasconi says they reflect the different trade-offs made between aerodynamics and hydrodynamics.

Or simply put, “you have to accelerate to get out of the water, and then once you’re up and frustrated, it’s all about the aerodynamics,” Bernasconi explains.

“The idea is that as the boat accelerates, we quickly reduce the volume of the hull in the water and the boat becomes more like a narrow multihull than a large monohull. There is also the aerodynamic benefit, which all teams have seen, that By having a skeg divider in the center of the boat, it creates a pressure difference between the windward side and the leeward side. ”

“We have done a lot of work on optimizing the design. With the tools we have, we are confident in the shapes we have created. Ultimately, we have to make some kind of judgment on the hydro and aerodynamics and look at the low wind performance together. with frustrated performance. ”

“It’s an interesting design problem for the engineers, and it’s great for us to have a really open space to play,” he adds. He freely admits that the latest from ETNZ looks nothing like the designer helmet shapes they first envisioned, when they wrote the AC75 class rule, in 2017/18.

Overall, Bernasconi says he expects the new boat to be better in all respects than the Te Aihe “through the region of acceleration and better aerodynamically.”

The reed arms have some significant differences.

The hull recess to take the axis of the foil is more refined than in Te Aihe and is again an aerodynamic and hydrodynamic improvement. The waterline beam (free area beyond the centerline point) appears to be wider, which provides more stability to help lift the boat off its blades.

One design feature that Bernsaconi will not explain lies in the arms of the sheet around where they enter the water where they widen about half a meter, before being reduced again to the standard width.

Another area where we are told to wait and see is the platform, which Bernsaconi agrees is an important development area. “It’s the only thing that pushes the boat forward,” he says. “Everything else is holding him back.”

“We have to put as much effort on that side as on the plates and the helmet,” he adds.

Te Rehutai is expected to sail the Waitemata for the first time on Friday.