Update
Top: Team NZ and Luna Rossa were the most similar of the new AC75s – both targeted at the 8-14kt wind range. Unfortunately for the Italians, the Louis Vuitton final saw more breeze and at times the silver stallion looked difficult to keep under control. Both boats could out-turn and out-accelerate Ineos in her early LV Cup trim and TNZ maintained the superiority into the Match, the British boat also throwing up disturbed water more than the other two. However, given a sniff of decent breeze, a few waves and a long enough runway and the Ineos design could suddenly light up – especially downhill when she was quite often the fastest thing on the water
a major factor in their performance. The grinding pedestals were put in cockpits, keeping the sailors out of sight and out of the airflow. The same was true for the trimmers and the winches for the jib – out of sight. At foiling speed the apparent wind was so far forward that carrying a spinnaker or Code 0 just added drag; there would be no sail changes during racing. The one-design foil arms, the hydraulics to cant them and batteries
to power the pumps were all supplied equipment. Each team designed their own foil wings and flaps to attach to the foil arms and their own rudder rake control system. Every adjustment of foils and rudder was powered by batteries. Not so for sail controls – everything above the water required human power, but cyclors were forbidden. All four teams built two AC75s. The sailors mastered these new beasts and we had good racing in Auckland. The AC75 doubters were silenced. For AC37 the new version of the AC75 Class Rule refined the
concept. The all-up weight was reduced and the span of the foil wings was increased – both changes to make it easier to take off in light wind. Reducing crew from 11 to eight sailors helped with the weight reduction but also reduced available muscle power to pressurise the hydraulic controls. Cyclors were allowed to offset that power loss. Interestingly, the grinding stations had to use rotary, not reciprocal
motion. The rule writers had apparently realised that elite oarsmen would be good candidates to power the pumps. New Zealand rowing legend Rob Waddell had been a grinder on ETNZ’s AC72 catamaran in San Francisco in 2013. Waddell won the gold medal in single sculls in the 2000 Sydney Olympics. He held the world record for indoor ergometer rowing for 19 years. Many of the cyclors in Barcelona were former elite oarsmen. The first version of the rule had strict limits on control systems
because of the concern that teams would find loopholes that effectively allowed an autopilot. With the experience gained in 2021, the new class rule allowed more linked controls. As an example, adjusting the mainsheet could be linked to jib trim. Sailors had to initiate any trimming, but the control system could complete the task – a button push could cause the mainsheet to be trimmed to a pre-determined load of,
16 SEAHORSE
say, eight tonnes, or to a pre-set sheeting angle – maybe 5°. Each team was allowed to build one new AC75 for the 2024 event.
Given that the four existing teams had each built two boats for 2021, the new yachts were the third generation. Normally that would mean convergence of designs, but Bernasconi said he was surprised by how different all the boats looked. American Magic had their helmsmen and flight controllers side by side and put their cyclors on recumbent bikes facing aft, allowing them to design a low, aerodynamic hull. Alinghi had a dramatic hull shape. Ineos put their flight controllers in the aft cockpits to give them a better view of the foils and of the situation on the racecourse. ETNZ and Alinghi both had their helms in the forward cockpits with the cyclors behind them. In 2021 Luna Rossa had successfully pioneered the concept of
having two helmsmen, avoiding the need to have crew cross the boat during manoeuvres. All the teams adopted the two-helmsmen setup for 2024. Luna Rossa put their flight controllers in the forward cockpit with the helmsmen just behind them. All of the teams also followed Luna Rossa’s example from 2021 with a boomless mainsail with a boom-equivalent below the deck. So the expected convergence in design was not apparent. When
all the new AC75s were launched ETNZ design head Dan Bernasconi said that, while he was surprised by how different they looked, he predicted that they would still converge in performance, and he was right about that. Foil wing shapes did converge during the development phase. The
2021 AC75s had a fairly wide range of foil wing shapes, some with anhedral and with varying chord dimensions. In this cycle, after a short period of early experimentation, all the teams arrived at similar high aspect ratio T-foils. All the teams have powerful computational fluid dynamics systems,
so they all were able to do in-depth analysis of design ideas. But what was each team’s design objective? At least two years ago they had to take into account the unique
sea conditions in Barcelona with waves sometimes coming from hundreds of miles away interacting with winds generated locally and
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