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Cup Spy: Alinghi Red Bull Racing make gains but AC75 is still a work in progress

by Richard Gladwell/Sail-World.com/nz 5 Oct 18:22 PDT 5 October 2022
Alinghi Red Bull Racing's AC75 attempts a foiling tack - Barcelona - October 5, 2022 © Alex Carabi / America's Cup

Alinghi Red Bull Racing has spent two long days on the water off Barcelona, as the crew work up their first generation AC75, purchased from America's Cup champions Emirates Team New Zealand.

Both days have been typified by typical Autumnal weather for Barcelona with light winds, sometimes building later in the day. We are well into the final month of the 2024 America's Cup at Barcelona. Today the wind in the afternoon was estimated at 7-8kts, building from 5kts earlier in the afternoon.

Fortunately for the Swiss team the seas have been slight with little cross swell apparent from video shot by the independent reconnaissance team.

On Tuesday October 4, team principal Ernesto Bertarelli joined the team for a day on the water to check progress, he was reported as being well pleased.

The tracking shows the team covered over 40nm during the course of the day, however some of this was spent under tow as the team changed location in search of more consistent breeze going in the direction of the airport.

It is not clear from the available content whether the AC75 was able to get foiling unassisted in these conditions, when the required takeoff speed is around 15-18kts. The normal practice, when training in these conditions is to tow the boat onto its foils and then release to continue sailing in the same way that a glider is launched behind a drone, before it starts soaring for the rest of the flight.

The purpose of towing up is to lift the hull and reduce drag from the main foil arms, but also to allow the AC75 to generate it own apparent wind and keep sailing once the tow is dropped. However it is unusual to be able to execute a foiling tack or gybe at the end of a run in such light winds, and this is what happened to the Swiss.

When used the towline appears to be very thin indeed, to be almost imperceptible, and usually only be seen against a contrasting background colour.

Two foiling gybes and three foiling tacks were attempted. None were successful, which is the expected outcome in these circumstances and stage of the AC75 campaign. It is assumed that the Swiss have kept the first generation AC75 in the same mode required in the class rule, meaning that the Version 1 boats are about 1000kg heavier than the Version 2 designs which won't be seen for 12-15 months. The heavier weight makes foiling more difficult in the light conditions, which is what is being seen with the Swiss. It is not known whether they are sailing with eight crew permitted for the 2024 America's Cup, or if there is the full complement of 11 sailing crew permitted for the 2021 America's Cup. The difference in weight will be about 300kg more for the Boat Zero foils to lift in light conditions.

Session Statistics - Barcelona October 4, 2022 - Alinghi Red Bull Racing - AC75 Version 1

  • Wind Strength (PM): 7-9 knots Wind Angle: E (PM)
  • Sea State: 3
  • Temperature: 21 degrees
  • Crane in: 0900 Dock Out: 1300
  • Dock In: 1745 Crane out: 1815
  • Total Tacks: 3 (Displacement)
  • Total Gybes: 2 (Displacement)
  • Estimate TWA: 90 degrees
  • Sails: M1- 1R with J1-3L (1 hour 50 mins).

An improvement on Wednesday

On Wednesday October 6, the Swiss team was again on the water off Barcelona in similar conditions to the previous day, however the breeze built during the four hour session, with only a modest increase in sea state, being a slight wind chop, and possibly a small swell. Like yesterday the wind strength was estimated at 4-5kts early in the afternoon building to 7kts from the East later in the day.

The recon team reported that one of the six tacks attempted today did not result in a touchdown - which in the conditions is a significant gain. Both gybes resulted in a touchdown. The final tack of the day was marred by a foil operation error by the crew. Unlike the Emirates Team New Zealand crew which made the same error on their AC40, on the same day in Auckland, the error did not result in a capsize.

Wind conditions at the end of the session should have been enough for the AC75 to get foiling, however only one video clip shows this happening - in what appears to be an easy lift off, with minimal wash appearing off the main foil arms as the AC75 accelerated to takeoff speed. In the one clip unassisted showing lift-off, the AC75 gets foiling before the bow dips back into the water, possibly catching a swell, before lifting back out again and getting up to foiling trim and speed.

In the videos ARBR's Boat Zero appears to be sailing in a normal fore and aft trim and ride height - similar to Te Aihe when sailed by Emirates Team New Zealand, and without the bow down posture that ETNZ's second, and 2021 Cup winning design Te Rehutai adopted, and seen again on the recently launched AC40. The reason for the bow-down attitude on the later designs is to improve the end-plate effect between the rig and the water surface and improve aerodynamic efficiency.

It will be interesting to see if the Alinghi RBR design team adopt the same cutaway after section, used by principal designer Marcelino Botin in American Magic's second AC75, Patriot, to help get the boat clear of the water during lift-off. The draggy aft section is a noticeable feature of all video seen to date in marginal foiling conditions.

It is not known whether the Swiss are sailing under an automated flight control system, or are flying the AC75 manually - something that is cannot be seen on the video, and about which the team has not been asked to date.

The Swiss team are expected to resume sailing on Monday.

Session Statistics - Barcelona October 5, 2022 - Alinghi Red Bull Racing - AC75 Version 1

  • Wind Strength 5 knots (AM) 7-8 knots (PM)
  • Wind Angle: E (PM) Sea State: 3
  • Temperature: 21 degrees & sunny
  • Crane in: 1100 Dock Out: 1310
  • Dock In: 1750 Crane out: 1825
  • Total Tacks: 6 (Displacement) 1 (Foiling)
  • Total Gybes: 2 (Displacement)
  • Estimated Speed of take-off: 17 knots
  • Estimated TWA: 90 degrees
  • Sails: M1- 1R with J1-1R (3 hours)

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