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Name three basic hull shapes4/29/2024 ![]() Also, the Americans at the beginning had the cockpit very far aft. “All the teams have cockpits on each side, with the crew well-protected from the wind to reduce drag. “The cockpits were pretty much the same everywhere at the beginning,” Fischer says. The third consistent element is the split cockpit. I think the only main difference is that on our boat, it’s a bit more obvious, but the others have more or less the same idea.” The American boat also has a pretty nice aero foil shape, and as well, the British boat. But in between the cockpits, the shape is pretty much like an aero foil. Fischer explains: “It is hidden because these relatively high cockpits on the side to cover the crew. If looked at sideways from the beam, all the second-generation hulls reveal an aero foil section from bow to stern-don’t be fooled by the high sides of the Kiwi’s crew pods. All the teams have paid enormous attention to this they hide the crew as much as they can, and have the shape of the hull as aerodynamic as possible, to reduce drag as much as possible.” “This drag component is comparable to the drag we see in the water. “If you stick your hand out of a car when you’re driving at that speed, you feel how big this drag is,” Fischer says. The speed of the boats drives this one, with apparent winds that can easily exceed 40 mph. The skegs are the most obvious element, but an aerodynamic hull shape is a close second. When we look at the four new boats, it’s clear there is significant agreement on what makes for a fast AC75. It was done with different means between the various teams, but we went for this very squared bustle to try to create a vortex off the sharp edge that would effectively seal. It’s interesting to see that all the boats have gone there now. We finally made the call to go there to try to achieve it. “We spotted early in the project,” Muyl adds, “and always questioned whether it was a true phenomenon, or whether it was an artifact of the computation. But make big efforts to close that gap as much as possible,” Fischer says. “So, even if you had perfect control of the boat, it would be impossible to close that gap completely. It’s impossible to completely seal the hull to the water without increasing the hydrodynamic drag, and even maintaining the minimum distance is made harder by waves. So, what’s happening is that now there is a gap again, so we pushed to effectively seal the hull to the water.” On these boats (the AC75), for the first time we have a monohull that’s flying. And then that was also seen on the AC72, and since then all the Cup boats have the mainsail sealing on the deck. It pretty much started with the Groupama C-Class boat for Cammas. “In recent years, we’ve seen sails and wings extend to seal to the deck. It should be no surprise, therefore, that their thinking is aligned here. Muyl worked with both Fischer and ETNZ’s Guillaume Verdier on Franck Cammas’ Groupama 5, the International C-Class Catamaran Championship winner. To avoid that, on all the boats, we see deck sweeper sails.” On a normal sailboat, this circulation that makes you lose lift is at the bottom, underneath the boom, and this loss is quite significant. “And obviously, the air tries to flow from the high-pressure side to the low-pressure side, and if you let it do that, you lose lift. “On every wing, you have a high-pressure side and a low-pressure side,” Fischer explains. ![]() ![]() This allows the boat to fly closer to the water, which has another important aerodynamic contribution. They enable better acceleration at slower speeds, and reduce the hydrodynamic drag and deceleration on touchdowns. This is the reason all four boats have skegs they provide a benefit in all three areas that Muyl and Fischer describe. And the other part of it, which is actually very important for these boats, is the aerial performance of the hull.” So, the ability of the hull to develop little drag when touching the water at speed or out of tacks, or out of jibe. The whole righting moment comes from the foil, so then the hull shape is all about takeoff capabilities, so effectively slowish speed, in the order of 16 to 20 knots-the touchdowns. Now the architect, he sums up the factors driving the performance of the AC75: “As soon as we decided that these boats are only going to race in flying (foiling) conditions, then there’s no point in having any righting moment from the hull. Benjamin Muyl is on his second Cup with Ben Ainslie’s British challenger, having been involved in the event since 2005. ![]()
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