Orient Express Racing Team

America’s Cup: what are the differences between the AC75s ?

The sixth and final AC75 built for the 37th America’s Cup, that of the Orient Express Racing Team, was christened on Wednesday in Barcelona. In anticipation of the first official confrontation during the preliminary regatta in Barcelona (22-25 August), Tip & Shaft sought to find out more about the design of this third generation, with four French architects and engineers involved in the teams: Philibert Chenais (Ineos Britannia), Dimitri Despierres (American Magic), Sam Manuard (Alinghi Red Bull Racing) and Benjamin Muyl (Orient Express Racing Team).

Whether contested in monohulls or multihulls, on ballasted or flying boats, the America’s Cup remains a great competition in naval architecture. Since the first images were unveiled, those of Alinghi Red Bull Racing’s AC75 at the beginning of April, there has been a succession of christenings and launches – the most recent being that of Orient Express Racing, christened on Wednesday – with their share of photos and videos, scrutinised by all the teams in an attempt to understand each team’s approach.

The six boats, which will be competing from 29 August to 27 October in Barcelona, are the third generation of AC75s for a second generation of measurement rules (two boats were allowed for the 36th edition). The rules have changed very little, according to the architects and engineers, and are very strict, particularly in terms of displacement and the position of the centre of gravity, not to mention the one-design parts (mast, foil arms and jacks).

In these conditions, it’s not surprising to see, according to Dimitri Despierres, a clear convergence” on certain architectural or steering-related aspects. “We can’t analyse the profiles, the flaps and all the complexity of the appendages on the photos, but I notice that all the foils are now T-shaped, with very similar and relatively small surfaces. That’s the lesson of the New Zealand design of the last Cup and also the result of making boats lighter”, notes the engineer who is embarking on his eighth campaign since his first as a crew member on 6ème Sens in 1999!


Ineos Britannia’s radical choices


As for the hulls, on the other hand, the contrasts in style are striking between Ineos Britannia, with its very pronounced shapes, and American Magic or Prada (Luna Rossa Prada Pirelli), which have focused heavily on aerodynamics, or even the stern of Alinghi, whose cockpit ends in a wing with a vertical trailing edge”, says Benjamin Muyl, who was in charge of understanding and interpreting the New Zealand plans for the French challenge, purchased from the Defender, at the same time as providing “design learning” for the sailors on the simulator.

Everyone agreed that the British boat seemed to be the most radical of the fleet, with its fairly high hull, the bulge in its deck and the very fine, deep water inlets in its hull bottom (the famous bustle), which ends well forward of the rudder, unlike the others. “The deep bustle is designed to close the gap between the hull and the water, to prevent the passage of leeward air, which disturbs the sail plan,” explains Philibert Chenais, platform leader of the British challenge.

And the man who is taking part in the British challenge for the third time, alongside chief designer Martin Fischer, who has moved from Luna Rossa to Ineos Britannia, adds: “Other aspects of our boat may seem counter-intuitive, such as the level of the deck we’ve raised. However, this is what produces the best results on the CFD studies we have carried out, in collaboration with Mercedes, who offered us their strike force in this area.”

“Hull and deck are intimately linked and you have to understand that in flying mode, which is the most common mode, this assembly becomes just a platform for rig efficiency,” explains Sam Manuard, who was recruited by the Swiss challenge Alinghi Red Bull Racing at the end of 2021. “A lot of different compromises are possible, and after testing some very radical configurations, our choices have led us towards more versatility, in the same way as the Italians and New Zealanders have done.” Is this a way of saying that the British boat could struggle in the take-off phases or during the famous touch downs, frequent when the wind and sea don’t match up, which is a frequent feature of Barcelona’s very open field of play?


Recumbent bike on Patriot


The AC 75s are energy-hungry machines, so watts have to flow freely for the few dozen minutes that a regatta lasts. While the hydraulic foil jacks are controlled by a fleet of one-design batteries, sail trimming uses exclusively human energy from the pedals of the grinders seated on their bikes. In this area, American Magic has been particularly innovative: the cyclists are lying down, which has made it possible to lower the deck line of Patriot, the New York Yacht Club boat, by 30 cm.

A winning configuration in terms of aerodynamics and lowering the crew’s centre of gravity, but “less efficient in terms of power developed”, according to Benjamin Muyl. Still on the subject of the men on board, while all the teams have symmetrised their crews (as in the AC 40s, no one crosses any more when changing tack), the helmsman and trimmer are side by side on the American boat, whereas they are in line on the competitors’ boats. “You lose aero, but you move the crew’s centre of gravity forward, which means you can load the foil more and the rudder less,” explains Dimitri Despierres.


Control loops


As for the rigging, while the distribution between mainsail and headsails (J1, J2 and J3) seems fairly similar, the control systems, which are almost impossible to decipher from the photos, reveal different approaches, according to the people we spoke to. Emirates Team New Zealand, for example, has two separate sheets on two cylinders, which allow the pressure on the two edges of the sail to be managed differently. “They’ve come up with a slightly different system, with a boom fitted with edge rails, unlike other boats where the rails are attached to the sail,” confirms Sam Manuard. “All this mechanics is crucial for performance. The ability to adjust at high frequency, very quickly and very finely, is one of the keys.

Philibert Chenais agrees, saying that the real differences won’t be on the platform, but “on the foils, the sails and their systems. Who has the buttons, what do they control, what are the coupling strategies?” As far as the architecture of the boats themselves is concerned, there is little chance that the teams will be able to make much progress with their AC75s between the training sails, which began in the spring, and the preliminary regatta in Barcelona (22-25 August), just before the Louis Vuitton Cup kicks off (competition between the five challengers, 29 August-7 October).

“The rule is strict on the percentages of modifications that can be made and everyone has been investing in one track for the past three years. The big gain will be in the sailors’ learning curve. On the architecture, you gain hundredths, whereas a successful manoeuvre means a difference of several knots,” confirms Benjamin Muyl. An opinion shared by Dimitri Despierres, who believes that this 37th America’s Cup will put the spotlight back on the performance of the men, particularly around what is known as mechatronics, which enables several simultaneous actions to be combined in an automatic and calibrated way. “In the old rule, these control loops were possible, but now we work on closed loops, meaning that we can programme target values to be reached. We’ve opened Pandora’s box, and there’s no limit to what we can do.” We’ll be seeing the results from the end of August.

Photo: Pau Venteo / Orient Express Racing Team

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