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Cup Spy Special: Alinghi Red Bull Racing's new AC75 unveiled - the Backless Boat

by Richard Gladwell/Sail-World NZ 5 Apr 14:15 PDT 6 April 2024
Alinghi Red Bull Racing - AC75 - Day 0 - B1 - Barcelona - April 5, 2024 © Ugo Fonolla / America's Cup

First images and video from the AC37 Joint Recon Team attending the unveiling of the Swiss AC75 raceboat - the Backless Boat -one of the Challengers for the 2024 America's Cup.

The Swiss America's Cup challenger was revealed for just 20 minutes to a seated audience of VIPs, and fans cramming vantage points outside the gates to the base in Port Vell, where the six America's Cup teams are all located.

Aside from radically cutaway topsides at the back end of her hull, the Alinghi Red Bull Racing AC75 is headed in the expected design development direction from the AC75 race-boats seen in Auckland in 2020/21. Boat One has many of the features first seen on Emirates Team NZ's America's Cup Champion, Te Rehutai.

Designed by a team led by Marcelino Botin, the lead designer for American Magic in the 2021 America's Cup, the Swiss AC75 is an elegant boat that reflects the edges offered by the AC75 Version rule but is finessed by a traditional yacht designer who has produced fast yachts within multiple racing rules.

Botin can draw on design lessons from multiple sources including ARBR's Boat 0, Emirates Team New Zealand's first AC75, and the first AC75 launched. He has the learnings from the American Magic experience, which, despite its capsize, held the speed record in the 2021 America's Cup of 54.3kts.

He has also seen how American Magic - upgraded to Version 2 of the AC75 rule has performed in the flat water for which it was designed in Auckland and then in Pensacola, Florida - American Magic's home base. Then, in Barcelona's completely different sea state, with its wind chop and awkward off-axis swells, there is reverberation closer to shore from the sea wall.

Plus, of course, he has seen the performance in several locations of the Emirates Team NZ designed AC 40, which the team says is an advance on the Kiwi's America's Cup champion Te Rehutai.

Against that broad AC75 design background and experience, Alinghi Red Bull Racing's new AC75 shows the expected trend towards reduced aero drag in the forward part of the canoe body. The hull works as an end plate between the rig and water surface in an attempt to seal the interface between wind and water, reducing turbulence and minimising drag while enhancing the aerodynamic efficiency of the foiling yacht as an airborne entity.

Starting at the point when the bow makes contact with the water, we can see the usual plumb bow, with what appears to be a flared chine - a first response to the hull interacting with the Barcelona sea state. The chine shape was revealed in later photos and is a hull shape treatment intended to rapidly increase the buoyancy of the bow section, if it is immersed, than would have been the case if a more conventional bow section were used. It will provide lift to help keep the rest of the canoe body from being submerged in the way that we saw so many times with Boat 0, with a semi-submersible bow - which was a very wet boat. The "chine" is tapered and disappears into the canoe body under the "l" in Alinghi.

This feature is not unique, and was present using a different design treatment in Emirates Team New Zealand's very first AC75 Te Aihe, which was onsold to Alinghi Red Bull Racing, and was their BoatZero which began its days under the Swiss flag in early July 2023. It remains to be seen quite how the latest rendition works on the imaginatively named BoatOne.

In some images we can see a second hard line just below the "Alinghi," which alludes to a Te Rehutai/AC 40 snowplow bow treatment designed to thwart any major nosedive by the hull into an awkward seaway or a trip when foiling too high and stuffing the bow.

The shape of the hull bearers on the boat cradle also highlight the cross sections of the canoe body of the hull. While different from Te Rehutai and the AC40, the hull has quite a complex snow-plow bow sectional shape that was unique to the Kiwi AC75.

Moving aft, we can see a skeg developing, which has its genesis from where the hull chine fades and becomes quite pronounced as it moves aft. The skeg has been chopped off square at its end and is much deeper and more substantial than Te Rehutai.

The other surprise is how flat, and thin, the very aft section of the canoe body appears — again similar to the stern section treatment of Te Rehutai. However, the skeg is much deeper and maybe slightly wider and has quite a sharp turn into the flat run of the aft end of the hull.

On the deck, the sheerline rises as it moves aft, providing more protection for the cyclors and sailing crew. As we move aft, the line of the sheer is the correct aerodynamic response to what has been seen previously with tell-tale spray clouds from AC50s in particular.

The hull shape aft of the bow is confirmed by the hull support sections on the AC75 shore cradle - and again shows a strong Te Rehutai/AC40 influence.

The other unusual feature is the extreme cutaway of the topside running into the transom, a weight-saving response permitted by removing running backstays in Version 2 of the AC75 rule. The load previously supplied by the running backstays to tension the forestay and provide rig support is now taken up by the load on the mainsail leech. The effect is for the maximum load point to move forward from the to the We guess that structurally, the support for that function is shifted into a substantial below-deck, carbon structure possibly extending into the skeg cavity, back to the mainsheet traveller to take advantage of the depth available, while keeping the cockpit floor thinner and lighter.

Above deck view

Images of the Swiss AC75 taken from an elevated position show a strong Te Rehutai influence with the crew located in built up cockpit pits where the co-helmsmen, trimmer/flight controllers and cyclors are located.

Like Te Rehutai the deck is lowered which lowers the heel of the mast giving clear unobstructed airflows around the lower sections of the sails and rig - improving efficiency. The crew is not expected to switch sides in tacks and gybes - so the design focus is completely on the aerodynamics and rig efficiency, without any concessions to crew safety crossing the cockpit deck.

From the images below, we can also get a better perspective on the bow shape which shows the increased volume achieved by the use of a bow chine. Boat Zero - designed by Emirates Team NZ, with an IMOCA60 style bow also used a chine or topside knuckle to achieve additional volume and buoyancy, however Boat One appears to be a little more extreme in this regard.

The challenge for the Challengers is not to come up with a boat that is the speed equal of Te Rehutai, but to leapfrog the Defender's design and development program and come up with an AC75 that is significantly faster than the Kiwis.

We'll know by mid October whether the Swiss have done that.

Report from Justin Chisholm:

Alinghi Red Bull Racing rolled out their BOAT_ONE AC75 for the first time this evening during an unveiling ceremony at the team's base in Port Vell, Barcelona – making the Swiss boat the first of the latest generation AC75s to be revealed in the 37th America's Cup cycle.

Following a single resonant toll on the team's large bell, the new boat emerged from the shed at just after 2100 to applause from team members and guests on the forecourt and on three spectator large spectator boats.

Darkness, smoke, and multicolour light show made it hard to identify much about the nuances of the boat's design, but, besides a fine bow entry profile which appeared to flare quickly as you go aft, the most noticeable design elements were a very deep rounded bustle that runs all the way to the transom of the boat, and its slab sides that are cut away at the back leaving a wide open expanse of aft deck.

Our vantage point outside the team base was not elevated enough to see down onto the deck. As far as the boat's appendages were concerned, the foils were were encased in protective covers so hidden from view, but the t-foil rudder was on display, with no surprises in its shape compared to what we have seen before.

After the completion of a dramatic aerial ballet that saw around 40 harnessed acrobats suspended above the Swiss AC75, the boat was rolled back into the shed at around 2120.

The next expected launch is by Luna Rossa Prada Pirelli on April 13, 2024 - with Emirates Team New Zealand reported in Italian media to be launching on April 18, 2024

Additional Images:

This commentary was written and compiled from video, still images and statistical content extracted from the AC37 Joint Recon program and other material available to Sail-World NZ, including photo files and other on the water coverage from the 2010, 2013, and 2017 and 2021 America's Cups. Its format is intended to give Sail-World readers a snapshot of all teams' progress on a given day or period.

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