America's Cup: The first week - two very different AC75's compared

by Richard Gladwell, Sail-World.com/nz 15 Sep 2019 03:50 PDT 15 September 2019

The America's Cup has gone up several gears, triggered by the launching of two AC75's and the sailing of one of the new class. The two AC75's launched to date have little in common other than they are 75ft long, are sloop rigged, and are 13.5ft between the Foil Arm rotation pins.

The basics - hull profile, rig style, foil fairings, foil wing shapes, deck and cockpit layouts - are all markedly different. And that is just comparing the pieces we can see or have been shown.

In terms of the generic America's Cup Class, we are now back in the same situation which for monohulls last occurred in the opening stanzas of the 1992 America's Cup, and for multihulls in the 2013 America's Cup. We should expect to see big design diversity from the different teams. One of them will be more on right track than the others. But none will be perfect.

We'll have to wait until race results sort out the most suitable approach - and then expect the the boats will begin to line up in the same corner of the Class Rule. With the way the timings of the Americas Cup World Series have worked out, that alignment probably won't begin until the 37th America's Cup.

Emirates Team New Zealand launched last Friday, with some interesting hull features the most obvious of which is a bustle down the centreline of the hull, and two deep trench cockpits with a flat sweeping deck area between.

"Bustle" is a term which harks back to the days of the International Offshore Rule, where the hull was bumped for measurement rule purposes, breaking what would normally have been a fair curve. It was controlled by what was known as a "Hollows rule" where there could be no indentation in the hull form greater than a few millimetres.

With the Emirates Team NZ AC75, "Te Aihe", the bustle has nothing to do with beating a measurement rule. But like the bustle of the IOR days, it is there to trick the passing water molecules into believing they are seeing something different.

ETNZ's Head Designer Dan Bernasconi says the hull deformity comes into play when the AC75 starts the transition from displacement mode to foiling, and the monohull morphs briefly into a multihull.

"As soon as you get a little lift on the foils then you start reducing the weight on the hull. At that point, it will only be the "bustle" that is in the water, and it looks far more like a multihull shape. We're trying to minimise the amount of wetted area, and get as much of the boat as we can, up and out of the water. Every square metre of wetted area is friction, and that will delay the acceleration."

"We're trying to get up and foiling as quickly as possible because foiling is a lot more efficient."

The trade-off for the bustle is that some stability is being sacrificed.

That is the most noticeable difference between the second launched, and first sailing AC75 from NYYC American Magic which flew off Newport RI, earlier this week.

The US Challenger's hull is almost scow-like being with the beam being carried down the topsides before quite a hard turn of the bilge into a nearly flat bottom. While some through the fence images had emerged of the New York Yacht Club's Challenger, the full extent of the unorthodox hull shape was not revealed until Friday, when she was photographed under tow and also on the hard, at her base in Newport RI.

The NZ Defender also holds its beam down the topsides before starting a complex underwater shape comprising a mix of chines, hollows and ending in the bustle.

The deck and cockpit layout of the two AC75's seems to be quite different, given that there is only one useful image released of the NYYC American Magic.

Above the deckline, the US boat appears to be a very conservative approach with a conventional cockpit, and mainsail being set using a traditional boom, on top of a hull form that is designed to be as aerodynamically efficient as possible. Bernasconi's comment based on having seen a couple of not particularly informative images of NYYC American Magic was that they had "put more emphasis on the stability than they had on minimising the wetted area."

Emirates Team New Zealand has by their own admission gone for an extreme boat. We haven't seen the whole package yet, so for those outside the ETNZ bubble, judgement is still reserved.

In the extreme design stakes, the prize in the below the deckline division, would have to go to American Magic, with Emirates Team New Zealand winning the above decks award, even though we have only seen her mainsail only partially hoisted.

New York's hull shape is a big step away from what was seen on their 38ft prototype boat, which was designed to be a half-scale AC75 - however the hull was a McConachy 38. The Brits had the same thinking with their smaller prototype - which started like as a Quant 28.

The main feature of Te Aihe's deck layout is the two deep trench cockpits. The purpose of these was ostensibly to get the crew low down without adding to parasitic drag. In between is a large flat deck area, aerodynamically shaped in sympathy with the rest of the deck profile. Glenn Ashby conceded at the launch that how the crew got from one side of the boat to other would be something that would come from the sailing trials.

Having seen the mainsail near fully hoisted, and with plenty of sailcloth still draped across the deck, the smart money is on a deck sweeper mainsail foot. That endplate would tidy up a lot of airflow across the deck and the attendant drag associated with a rig that uses a mainsail boom - as used by American Magic.

The mistake, of course, is to be too judgemental at this stage of the launch cycle. These AC75's are development boats and over the next 12 months will have more cosmetic surgery than Joan Rivers.

Some video has already been released including one lengthy clip - big surprise for some (and relief for others) is that American Magic is so stable in foiling mode - quite a contrast to the dire predictions by some pundits who felt that the concept of a foiling monohull was too extreme for the Cup. Quite how the AC75 performs in 25kts and rough water remains to be seen - given that they will be sailing in 50kts of apparent wind, there are a few challenges ahead.

For Emirates Team New Zealand, who decided almost from the outset not to build a smaller development boat - there is the imperative to get the AC75 sailing and validate their simulator - on which they will place huge reliance for the design choices for Boat 2. Given that they don't have to be ready to race until March 6, 2021 - a couple of months later than the Challengers the Kiwis have a useful time edge.

Bernasconi says that one of the key answers they need to obtain from the new boat is the cross-over for the Code Zero. "It's one of the things that is hardest to learn from the simulator," he said at the AC75 "Te Aihe" launch.

When Sail-World interviewed NYYC American Magic's Terry Hutchinson he noted that the issue is that at lower wind speeds (say sub-10kts)the power generated by the Code Zero is essential to get the AC75 foiling. Once foiling the Code Zero will be furled, but the issue then is that furled jib must be lowered to reduce drag. Of course, if the wind softens and the Code Zero is viable - then the Code Zero has to be rehoisted, and deployed.

All sounds very technical, but hark back to the 2013 America's Cup, where Oracle Team USA worked out the cross-over for the Code Zero to headsail alone, was around 11kts of breeze, when the minimum windstrength to complete the course within the time limit was just under 10kts. Knowing that the time when the Code Zero would be useful was minimal (across a range of about one knot), they opted to dispense with the Code Zero, the bowsprit and gear - making the boat lighter and able to foil more easily.

That decision was one of the turning points of the 2013 America's Cup Cup, which Oracle Team USA went on to win by 11 races to eight.

"You definitely need a lot of power when the breeze is light," explained sailmaker/designer/trimmer/skipper Glenn Ashby to a media scrum at the launch of Te Aihe. "Being able to get the sails through a really deep range from light winds to heavy, and also upwind to downwind will be critical. The apparent windspeed upwind is phenomenal, and downwind while you are going fast, but it is a lot less, and you really need to get those sails through a massive shape and power range.

"That alone for the designers has been a huge challenge, and whoever does that well is going to put themselves in a great position for the Cup."

One of the features of the 36th America's Cup is that sail designers are once again a vital part of the America's Cup teams. They have plenty of scope with the mainsail size being dictated solely by a series of five girth measurements with minimums and maximums, plus a formula based on the five girths.

Jibs are even more open, with two sizes of jib contemplated plus a Code Zero - all of which are controlled by just three girth measurements - with maximums only stipulated.

Of course, there are other sail rules as to battening and the like, but the door is wide open for sail design to be fully integrated with all other parts of the design package - which is the way it has to be for any high-performance yachts to reach their true potential.

There are no limitations on the number of sails that can be built. However, the number of sails will be dictated by the nuances of the boat type, and the range through which one sail has to be effective, before being changed up or down.

Clearly, there will be a lot of work done in the simulators involving the relationship between boat performance and sail design. The critical decisions will be made long before the first sail panel is cut.

For AC75 sail wardrobes, less will be best. Versatility is the name of the AC75 sails game, and that will have significant spinoffs for the rest of the sport both in sail design and furling technology. American Magic seems to be the more conservative of the two as this stage, however their focus would seem to be more on understanding the nuances of their hull shape and foiling configuration rather than having the complication of an unorthodox rig configuration.

The Kiwi sailing fans have been treated to almost an information overload from their home team and media, and it has been lapped up.

At Sail-World, America's Cup stories have dominated the story ratings since it was first confirmed that a launch was imminent. Last month was a readership record for Sail-World with almost 640,000 stories being opened and read world-wide by sailing fans. America's Cup dominates the top topic list. But that record came before an AC75 came out of the shed, and revolved more around the two very different IMOCA60's aimed at the next Vendee Globe, that were revealed for the first time in August.

The Challengers have been notably quiet over the past few months - maybe they were focussed on getting their boats launched. The quantity of stories, images, social media, interviews etc. must be stepped up substantially if this America's Cup is to be the success it deserves, and indeed if the next edition of the Cup is to attract new teams and new fans.

One of the first comments, at the launch of Te Aihe, made by Emirates Team NZ CEO Grant Dalton, and echoed by others, is that anyone who wants to watch the 36th America's Cup will be able to do so on whatever device they have and at no cost.

The fans appetite for this Cup and the AC75 is massive, it must be fed, and Kiwis in particular enjoy nothing better than a free feed. This America's Cup promises to be a veritable smorgasbord for fans - both in sailing and mainstream sport.

This coming week we expect to see Emirates Team New Zealand continue sea trials.

Other than a morning spot of lighter weather on the Waitemata harbour on Wednesday, wind conditions were too extreme for test sailing last week.

Stay tuned to Sail-World for more images and commentary each sailing day. We also hope to publish more of the interviews with Glenn Ashby and Dan Bernsaconi quoted above from the launch on September 6, 2019.

We will also be running any news and images available from the four Challengers as soon as they come available.

NYYC American Magic released a video of their launch of their AC75 Defiant, which included some sailing video in what appear to be (by the state) to be light winds.

Impressively the team is able to execute a foiling gybe, although the video cuts away before the gybe is completed and and does not show if Defiant exits the gybe having successfully completed the transition from her port-side foil onto her starboard foil.

Still images from the American Magic video:

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