The fast and the furious

The AC75 yachts made a stunning debut in 2021, providing exciting, high-speed racing while flying improbably on an underwater wing the size of a surfboard. Visualise an eight-storey building on its side racing past you at 50 miles an hour and making turns as if it were on rails. It’s pure adrenaline.

Written by Jack Griffin

13 August 2024

For the 2024 edition of the America’s Cup, six teams have spent the last two years designing and building the second generation of these extraordinary machines, and the stakes couldn’t be higher. Now the new boats are in the water, in final preparation for the racing – so what’s changed in the design?

For a start, the 2024 yachts have only eight crew and all teams have adopted the two-helmsmen configuration that was introduced by Luna Rossa in the last Cup, with no crew crossing the deck during manoeuvres. This obviously simplifies the choreography and allows all crew to stay low in their cockpits, reducing aero drag. However, each team has implemented a slightly different configuration of crew cockpits and responsibilities.

The prediction that these second-generation yachts would trend to a similar design space appears to have been premature, at least as far as hull shape and crew positions go.

The race area is perfectly positioned for spectating from La Barceloneta’s beaches. MAP COURTESY OF AMERICA’S CUP.

Emirates Team New Zealand’s Taihoro takes its name from the Māori words for sea (tai) and speed (horo). Pic: EMIRATES TEAM NEW ZEALAND.

INEOS Britannia was able to draw on the expertise of the AMG Petronas Formula 1 team, of which Jim Ratcliffe has a one-third ownership.

Britannia has slab sides and a vertical skeg. Shifting crew weight forward could mean the rudder’s stabiliser produces downforce instead of lift.

But one area where all the designers seem to have come to a similar conclusion is foil shape. In 2021, we saw a wide range of foil shapes – straight, curved, thick, thin, even W-shaped. This year, everyone seems to have settled on thin foils, some with a slight downward curve. The boats are 1 tonne lighter than in 2021, and the foils have a 50-centimetre-longer wingspan.

Foiling is always faster than floating. This year, races in Barcelona will be held in as little as 6.5 knots of wind, so the ability to take off in light conditions and then stay on the foils takes on huge importance. Foil design, flap control systems, sail shapes and sail controls all contribute to sailing fast as well as staying on the foils.

All the teams have looked for creative ways to apply the design rules. We can see some of their design ideas by looking at how they’ve designed around those parts of the boat that are tightly specified by the rule.

The foil arms and the hydraulic system to raise and lower them are supplied equipment, which all teams must buy from a single supplier. The locations of the pivots for the foil arms are also fixed by the rules. The height of the mast rotation point is fixed relative to the foil arm cant pivots. Like the foil arms, the shrouds for the mast are supplied equipment.

The teams are, however, free to design the foil wings and flaps and the control systems for the flaps. Each team constructs its own mast, which must conform to a one-design specification, but extensions to the base of the mast are permitted.

Defender

Emirates Team New Zealand

Taihoro, Royal New Zealand Yacht Squadron

Emirates Team New Zealand’s Taihoro takes its name from the Māori words for sea (tai) and speed (horo). The Kiwis managed to squeeze 14 days of sailing into the three weeks between launching Taihoro in Auckland in mid-April and packing her up in early May for a sea voyage through the Panama Canal and on to Barcelona. They plan to resume training in Barcelona in early July.

In 2021 the Kiwis found a clever way to increase sail area, dropping the deck below the rules-imposed level of the mast rotation point. This allowed them to lower the foot of their mainsail, gaining power and lowering the centre of effort of the sail. For 2024, they’ve kept the lowered deck but have changed the stern of the boat dramatically from their 2021 boat. Rather than a flat, angular stern, the Kiwi boat has gentle curves from the aftmost crew cockpits to a curved transom.

There are four cockpits on each side, with the helmsman forward and the flight controller/trimmer just behind him. The leeward side helmsman can act as a tactician/strategist. There are two cyclors on each side. With the downward sweep of the sheerline, it looks like the cyclor in the aftmost cockpit may be high enough to add aero drag.

The AC75 uses a twin-skin mainsail. Unlike the other teams, the Kiwi boat has a separate hydraulic ram and mainsheet for each skin. They appear to have a boom located below the deck. Having two mainsheets allows them to control the twist of each mainsail skin separately. The boom allows them to transmit the mainsheet load efficiently to the hull.

The Kiwis sold a design package to the French team, so Taihoro has a twin – Orient Express Racing Team’s AC75 called Orient Express.

Challenger

Ineos Britannia

Britannia, Royal Yacht Squadron

INEOS Britannia Team Owner Jim Ratcliffe has one-third ownership of the Mercedes AMG Petronas Formula 1 team. After being eliminated in the 2021 Challenger Selection Series, the Brits gave major responsibility for their yacht design to the F1 team in Brackley, England. Their yacht – Britannia – looks noticeably different from the other teams.

The boat is slab-sided, and its high freeboard gives the crew deep cockpits to keep them out of the airflow. On each side, the two cyclors are between the helmsman and the trimmer/flight controller, who’s in the aftmost cockpit. All the crew positions are relatively far forward.

The yacht’s skeg terminates vertically, quite far forward of the rudder – all the other teams have a smooth transition from the centre bustle or skeg to the rudder. Moving the crew weight forward may allow them to use the horizontal stabiliser on the rudder for downforce rather than lift. This would increase righting moment, as the weight of the yacht is carried by the leeward foil.

The team built a test boat during the development cycle and had multiple breakages on the test boat’s rudder, which might have come from generating downforce. On deck, the housing for Britannia’s rudder is bigger than on the other yachts – possibly to enclose structural elements that can withstand downforce.

In 2021 the team had reliability problems, which continued with their test boat program in the lead-up to 2024. The AC75 is a highly complex boat; reliability and ongoing maintenance will be important to all the teams, perhaps most so for the Brits.

BoatOne features a pronounced chine in the bow, a potential game-changer in the confused seas of the Barcelona race area. Pic: © IVO ROVIRA / AMERICA’S CUP.

Luna Rossa’s skeg, which tapers gradually to the rudder, could make her very manoeuvrable in tacks and gybes, giving her an advantage. Pic: © IVO ROVIRA/ AMERICAS CUP.

Challenger

Alinghi Red Bull Racing

BoatOne, Société Nautique de Genève

The design team of Alinghi Red Bull Racing had access to Red Bull’s F1 designers but did not rely on them as heavily as did INEOS Britannia on Mercedes AMG. Team Founder Ernesto Bertarelli encouraged the designers to be daring rather than conservative, and the result is a sleek yacht with cockpits that end vertically, well forward of the transom.

The 2024 version of the AC75 Class Rule eliminated backstays, allowing the Alinghi designers to remove weight, with a flat deck in the aft section. On each side of BoatOne, the helmsman is forward with the trimmer/flight controller behind him and the cyclors in the two aft cockpits.

The Swiss team was the first to set up operations and sail in Barcelona, a venue known for its often-confused sea state where the waves and swell are often not aligned with the wind direction. The Alinghi yacht has a distinct chine in the bow section, possibly to help deal with Barcelona’s waves – compare this to the British approach to handling the sea state, with a very full, almost bulbous forward hull section. Alinghi’s foredeck is raised, which may be simply to meet the volume requirements of the AC75 Class Rule, but more likely it contributes to the aerodynamics of the yacht.

The hull has a skeg running the full length of the yacht. This creates an end-plate effect, preventing wind from flowing crossways under the yacht, and allowing the sails to capture more of the wind’s power. The skeg runs in a mostly straight line from bow to stern, with no rocker. Like New Zealand, the Swiss added a mast extension and additional sail area below the height of the mandated mast rotation point.

Challenger

Luna Rossa Prada Pirelli

Luna Rossa, Circolo della Vela Sicilia

Luna Rossa is arguably the most visually stunning new AC75. The yacht has a fine entry in the bow, and the hull has very smooth lines with no sharp angles.

Luna Rossa differs from Alinghi and Britannia, with a gradual taper of the skeg back to the rudder that should make the yacht very manoeuvrable in tacks and gybes. It also means the rudder rake controls are housed above the deck.

A Plexiglass windshield for the helmsman keeps him out of the airflow, providing good visibility. Like the Kiwi boat, the trimmer/ flight controller is behind the helmsman, with the cyclors in the two aft cockpits on each side. The deck is scooped out, with smooth flowing curves rather than the angular shape of Alinghi’s crew pods. The one-design mast has an extension to allow more mainsail area below the level of the mast rotation point.

Angular graphics on the hull disguise a very aerodynamic shape with low freeboard on Patriot – will that make all the difference?

Orient Express, which is the same design as Taihoro, has twin mainsheets to allow the twist of each of the mainsail’s double skins to be controlled separately. Pic: ALEXANDER CHAMPY-MCLEAN / ORIENT EXPRESS RACING TEAM.

Challenger

American Magic

Patriot, New York Yacht Club

NYYC American Magic has clearly opted to minimise aero drag with its design for Patriot. The boat has very angular graphics that disguise the smooth, flowing hull shape. American Magic’s yacht has the lowest freeboard, and we can see just how low the freeboard is by looking at the terminations of the shrouds.

Remember that the standing rigging is supplied equipment, so the shroud length is fixed – Patriot’s shrouds terminate above the sheerline, unlike all the other boats.

American Magic achieves the low freeboard in part by putting the cyclors on recumbent stations, facing aft. This configuration allows the sheerline to taper smoothly down as it runs aft. The Americans claim the recumbent cyclors generate as much power as they could on vertical cycles.

Like Britannia, Patriot has the crew as far forward as possible. Their unique cockpit layout has the helmsman and trimmer/flight controller sitting side by side. Like on Luna Rossa, the skeg tapers upward smoothly toward the rudder. This almost certainly contributes to better manoeuvrability – the sailors describe the boat as far more agile than the 2021 incarnation of Patriot.

Over the coming weeks, the teams will continue to develop their yachts, testing minor modifications, and will spend more and more time training on pre-starts and manoeuvres, which should give further clues to their design choices. In the next issue, we’ll look at how the sailors will race these amazing yachts.