Design Insight: T5 & AC75

Yachts and Yachting's Toby Heppell spoke to CEO, Grant Simmer for a design insight on T5 and the AC75

When the new class to be used for the 36th America’s Cup was announced last November, it caused quite a stir. With Emirates Team New Zealand having promised Challenger of Record, Luna Rossa Prada a return to monohulls, everyone knew that the foiling catamaran era would come to a close. What most did not expect, however, was quite such a radical design. The concept of the keel-less, foiling, soft wing-sailed, 75 foot monohull is unlike any other boat in the world and was radical enough that it has caused genuine debate as to whether such a craft would actually be able to sail at all.

As the first time that an AC75 may be sailed is spring 2019, we are still some way from a definitive answer as to whether it will work. The closest proof we have so far comes from Ben Ainslie’s British America’s Cup team (now known as INEOS TEAM UK) who have been spotted screaming around the Solent in their 28ft test model. This boat, dubbed T5 by the team (continuing their nomenclature from the last Cup cycle where their test cats were T1-4) started life as a Quant 28 – a lake boat of Swiss design based on partially lifting DSS foils designed by Hugh Welbourn.

It is hoped that the test platform will give the Brits something of a head start over the other four teams entered – despite Emirates Team New Zealand and Luna Rossa Prada arguably entering proceedings with a head start, having come up with the concept in the first place. It is also clear that INEOS TEAM UK are using the boat as a marker that they have learned from their mistakes in the 35th America’s Cup.

Learning experience

Not for nothing is Ben Ainslie the greatest British sailor in Olympic history. Ashore he is softly spoken, affable, bordering on shy at times. Anecdotally, however, he is incredibly different out on the water and will stop at nothing to win.

It is this absolute commitment to winning that has served him so well across his four gold and one silver medals but the America’s Cup is a different beast. The age-old mantra that the fastest boat always wins the Cup is undoubtedly true. Being the greatest sailor is of little consequence if you have a slow boat. And now that the 35th America’s Cup is in the history books Ainslie is frank about the mistakes that were made in that campaign: “To win the next Cup, what you need on the startline is a boat that can win us the Cup, and that is something we did not have in Bermuda,” he explains. “We did a lot of analysis after the event and some things we did really well. I remain incredibly impressed by how well the whole team pulled together in the time we were in Bermuda and how much we managed to improve our performance when we realised that we were very far off the pace. Ultimately though, that is a position I would never like to be in again.”

New designers have since been brought in, the hugely experienced Grant Simmer (winner of multiple Cup campaigns) is now at the top overseeing things and, crucially there has been that financial commitment by INEOS. Perhaps more than anything, acceptance of Jim Ratcliffe’s blanket investment is a strong signifier of Ainslie’s unending ambition to win sailing races.

Ainslie is clearly convinced this is the path that must be taken to win this version of the America’s Cup. “The moment we saw the protocol which said teams could build two boats, and saw the class rule it was pretty quickly clear that this would be a two boat campaign if you are serious about winning it,” he says. Thus the £110m investment from INEOS secured the team’s two boat ambition and provides the sort of money needed to produced test boats like T5.

Building T5

With CFD (computational fluid dynamics) testing almost as good as real time testing of a boat, it raises the question as to why INEOS Team UK are building a test boat? After all, one of the creators of the AC75 rule, Dan Bernasconi has publicly stated that he did not think it would be worth building a test boat.

Grant Simmer explains: “We decided to build T5 for several reasons; firstly this concept of boat - the AC75 - is an entirely new concept, there hasn’t been another boat sailing like this and we wanted to be out there with Ben and the sailing team, getting to experience this boat. It’s an opportunity to learn to sail a foiling monohull like this. “Secondly to learn from the control systems, which will ultimately lead us on to the control systems on the race boat.”

But of course with CFD modelling featuring so prominently in the last decade or so, the team will be working hard off the water too: “In parallel with the on-water testing we are also doing computer modelling, including using a simulator. Simulation has been a big change in the yachting world – led by the New Zealanders in the last Cup – so you can do tests on the water and then replicate the test on the ‘sim’. “This process has been really valuable for the design team and will help us with development of the AC75.”

Hull shape designs

The design of the AC75 is already well underway. It is quite easy from the outside to assume that there is still plenty of time before the America’s Cup in 2020 rolls around but in truth, with one AC75 launching in 2019 and the next in time for the Cup in 2020, design for the main hull at least needed to be finalised recently.

As the hull shape is one part of the class which is relatively open, it is expected that there will be some visual differences between the boats. A key element to get right and something that’s likely to manifest itself clearly in different designs will be that all-important factor of switching between non foiling and foiling - particularly as the AC75 is only expected to get up on the foils at around 8 knots, so there is scope for some entirely non-foiling races.

Given the time constraints involved in building and launching T5, input from this boat will not be going directly into next hull design, as you might think. “With T5, the hull shape development was not really part of the project and we just chose a hull that was suitable for our purposes,” Simmer explains.

“But it’s fair to say that [beyond the hull shape] we have learnt a lot from sailing the boat. It’s not necessarily all come as a surprise, as we have done a lot of simulation at the same time, but there are a few characteristics surrounding the dynamic behaviour of the boat that have surprised us – at times it has been quite full on. Because of some of the scaling effects it doesn’t accurately model the AC75, but it has been a cost effective solution for us to learn more about this new style of boat.”

Stability issues

That point on dynamic behaviour in a smaller boat is worth noting. The dynamic behaviour of a boat reduces significantly as you go up in size. What this means in reality is that, though we have seen a number of capsizes, splash-downs and various other wipeouts by the team as they put T5 through its paces, we are likely to see fewer crashes from the 75s themselves, though Simmer seems to think there will still be a few: “We are expecting that there will be capsizes in the AC75 and we anticipate – and hope – they will be less full-on than some of the capsizes we’ve had on our small test boat.”

Here at Y&Y we have heard of some significant capsizes in the test boat, but Simmer won’t go into any more detail about how severe these may have been. But we certainly got some idea of how unstable a boat T5 is when we saw the best sailors in the world heading out onto the water the first few days after T5 was launched with inflatable stabilisers attached to the boat to stop it tipping over! The thought of these scaled up to 75ft is, frankly exciting and scary in equal measure.

Foil developments


The arm of each foil is set to be one design and the components that lift them will be supplied too. However the shape of the lifting foils, the flaps on the foils and the way in which the control systems work will all be unique to each team and this is a key area Simmer says they have been looking at. “I think we will see a variation in the geometry of the foils, and in the control of the foils, that will be a critical part of the AC75 and not all of it will be visible to the casual observer.”

Already the team have been testing foil shapes, and also trialling how the foils are controlled. With just two sailors onboard T5 there has been much discussion as to whether the sailors are controlling the foils or whether that is being done off-boat, perhaps from a support RIB. But Simmer is not giving any detail there, merely stating that “our control systems are propriety” giving you some clue, at least, as to how important they think this area of development will be come the final Cup class. Hopefully, with the Brits’ jump-start on development, they stand the best chance of winning.

The November issue of Yachts and Yachting is out now