This would imply that the longitudinal position of maximum lift would be somewhere near the foils. Perhaps, when the boat is heeled to weather and getting ready to take off, the water flow on the windward side reduces leeway by sucking the boat up to windward which helps to get the leeward foil working?
There’s also a question whether the box type section of the skeg provides a lighter structural beam to make the hull stiffer fore and aft. If this is the case it could be that space has been freed up inside for systems and/or that it means the weight budget for structure can be used in other areas.
Another interesting feature is the distortion in the hull shape aft which appears to be a way of reducing the waterline beam and therefore wetted surface area quickly as the boat lifts, which in turn will provide a step change in acceleration – a performance aspect that will doubtless prove critical on a race course that has plenty of corners and boundaries to accelerate away from.
“Slow speed manoeuvring is quite difficult and the initial stage of acceleration is tricky,” said team pilot Leigh McMillan, the crew member responsible for flight. “[But] the acceleration through the mid-range is going to be a huge step forward.”
Over 170 years of America’s Cup racing, Britain has what can only be described as the longest losing streak in history. The Brits were left bruised after defeat in Bermuda, and there have been a few changes since then.
On the AC75 Giles Scott is calling tactics for skipper Ben Ainslie, with Leigh MacMillan as flight controller. Add in Cup veterans David Carr and Nick Hutton, and some additional muscle from the likes of Olympic rower Matt Gotrel, and the team seems settled and tight-knit.
When viewed in elevation, the hump in the sheerline from midships aft seems to highlight just how important aerodynamic lift is and how the deck can now be used to contribute to lifting the 7-tonne beast out of the water.
“We’re pretty happy with what we have done and the evolution of our boat,” said chief designer Horacio Carabelli. “I think we have stepped up pretty well. It’s just small details that we really improved from our first generation boat.”
Although Carabelli and the team were keen to play down any developments that may have taken place between boat one and boat two, the 2020 chatter was about how sophisticated their first boat looked.
two challengers for their first boat and have since been able to concentrate on other details that are less obvious. They were the only team to mask out shots of the twin cockpits.
The Luna Rossa Prada Pirelli team hasn’t been afraid of ruffling a few feathers in the run-up to this Cup, but helmsman Jimmy Spithill isn’t the type to be bothered by a bit of conflict.
With a Cup record equalled only by Russell Coutts, Spithill is a very hard man to bet against. Team skipper Max Sirena has also been on the winning side both alongside and against Spithill, with USA 17 in 2010 and ETNZ’s winning crew last time.
Photo: Sebastian Slayter/American Magic
The boat – Patriot
The American team were first to launch both iterations of the AC75. On the face of it, Patriot looks much like her sistership Defiant, but the differences start to become clear when you look at her bow.
Gone is the scow shape with its overblown Topper dinghy-style deck and flat bow sections and in comes more of a V-type bow, albeit still under a beamy foredeck.
Here, the flared forward sections create the start of the centreline skeg that runs aft for around 75% of her length. Skegs have become a feature of all four new boats as designers attempt to maintain the seal between the hull and the water’s surface for as long as possible in order to maintain aerodynamic efficiency.
American Magic’s slender hull and curved deck is influenced by the smooth aerofoil shape of an aircraft’s wing. Photo: Will Ricketson
“The flare in the bow is just maximising the driving force and minimising the heeling moments that you’re producing,” explained designer Marcelino Botin. “The bow shape and the whole boat is guided towards that objective.”
Apart from a high gloss finish that is very effective at concealing what she really looks like, Patriot is notable for her smooth, undistorted shape below the waterline and her aerodynamic shape above.
“You should look at the hull shapes as a continuation of the rig and the sail plan,” continued Botin. “What you’re trying to achieve with the hull is to maximise the driving force of the rig and the sails and minimise the heeling moment, it’s as simple as that.”
If you look at all of the designs with this in mind you can see areas where this is the case: one example is the wide flat central section of the deck between the crew (who are lined fore and aft up along each gunwale), which dips gently towards the cockpit sole as it sweeps aft keeping the airflow over the deck and around the bottom of the mainsail clean.
With apparent wind speeds that are regularly in the 40-60 knots range it’s not difficult to see how a curved deck like this can act as a lifting device; there are plenty of aircraft that fly at these speeds and less.
Photo: Will Ricketson/American Magic
Another notable point is the depth of the rudder. The top of the blade has a long chord to provide control at slow sub foiling speeds while the lower tip of the blade is a painfully skinny affair to reduce drag and avoid cavitation.
It will have been a strange homecoming for Dean Barker when he arrived back in New Zealand to take the wheel of Patriot. Barker was the country’s hero when he won the Auld Mug for the black boat in 2000, but after losing twice to Alinghi and then to BMW Oracle in 2013 he was removed from the skipper position and has been helming for other nations since.
As well as skipper Terry Hutchinson, much of the team’s DNA comes from backers ‘Hap’ Fauth and Doug DeVos’s successful Bella Mente and Quantum Racing programmes.
Photo: Gilles Martin-Raget
Emirates Team New Zealand
The boat – Te Rehutai
It’s difficult to overstate how eagerly anticipated this new launch was. Besides being the current America’s Cup holder, Emirates Team New Zealand has set the foiling agenda since 2012.
Being the architects of the new rule delivered another opportunity to stretch further ahead. This is how the Cup works: win it and you get to make the rules. This is a design team that has been ahead of the curve for two consecutive Cup cycles already.
The most striking aspect of the new boat is how similar in concept it looks to that of INEOS Team UK. Despite their different starting points, the two teams appear to have arrived at a similar design place.
The aggressive, muscular approach is first evident with a long, deep and chunky skeg that runs the full length of the boat. Like on the other AC75s, this feature provides an aerodynamic seal up until the point at which the boat starts to take flight, plus it may also contribute to the hydrodynamic side force at displacement speeds.
Te Rehutai features a prominent skeg and flared hull. Photo: Gilles Martin-Raget
When viewed from underneath it appears to be a more parallel sided section than that on the British boat. It is also possible that this chunky skeg provides an efficient, beefy structural spar for longitudinal stiffness.
Then there is the heavy flare in the forward sections of the hull, which roll out into flat, horizontal sections aft.
Such clean flat areas pushed out to maximum beam result in vertical topsides, suggesting the Kiwis believe there is a well defined step between displacement sailing (where maximum form stability will be required), and flight. The complex underwater shapes of the British approach suggest that there are more stages to this transition.
It is this transition, and how it impacts on the ability to accelerate quickly, that is one of the key cornerstones of performance, as confirmed by ETNZ’s head of design Dan Bernasconi.
“We’ve been searching for the perfect balance between hydrodynamic and aerodynamic performance,” he said. “An AC75 that was optimised purely to accelerate and take-off would look very different to one which was optimised for steady flight, and that’s reflected in the huge variation we see between our competitors’ yachts in the fleet.
“Te Rehutai is designed to excel in both domains – the water and the air – and we’re confident she’ll be competitive across the range of wind-speeds we may see in the America’s Cup.”
There are few sailing partnerships as successful, and apparently as near-telepathic, as Pete Burling and Blair Tuke. The multiple 49er world champions and America’s Cup holders have an uncanny ability to get the best out of every boat they step on, so it’s no surprise that while Burling steers the AC75 Tuke will be flight controller.
The rest of the squad reads like a who’s who of yachting, from CEO Grant Dalton to a design team that includes Guillaume Verdier, not least sailors like Glenn Ashby and Ray Davies.
Defenders come out swinging
Just 18 hours after its launch, Emirates Team New Zealand took their new Version 2 AC75 on its maiden sail and flew round the Hauraki Gulf, writes Elaine Bunting.
The defender was the last of the four Cup teams to launch their second boat, but helmsman Peter Burling and crew put down a powerful marker with an impressive series of ‘dry’ tacks and gybes in just 6.5 knots of wind.
With first racing over 17-20 December, ETNZ will have had only three weeks to practice in the new boat whereas rivals American Magic, Luna Rossa Prada Pirelli and INEOS Team UK have been sailing since mid-October.
The Defender team’s chief operating officer, Kevin Shoebridge, admits: “The learning curve is pretty steep with modes and manoeuvres, and we don’t have a lot of time. We are a little bit undercooked. We are not 100% ready but we will definitely be sailing at the full potential of the equipment we have right now.”
But Shoebridge says there is much more to come: “The hulls are what people look most at, but the reality is you are spending a lot of the race out of water so the foil package is hugely important, the rudder, everything above the deck, the sails, all the control systems and the aero package. All of those things collectively will count,” he told us.
Sail development will carry on until the America’s Cup itself in March, and teams all have new foil wings and flaps on the way. However, these take months to build, ”so everyone is already committed to their final sets now,” says Shoebridge.
Foil control systems have been a fiercely guarded area of development that, as we saw in Bermuda, is absolutely critical, and not easily visible to observers. So although teams are not allowed to get close to each other outside competition, the long Cup tradition of spying has been flourishing.
“The reconnaissance side is really important and was something we did well in Bermuda. We had a very detailed recon programme, and everyone is doing it now, for sure,” Shoebridge tells us. “There is never a day that we are on the water without the other teams there, watching. There’s some smart things out there and if we think they are doing something well we’ll be looking at it for sure.”
Historically, the Kiwi team has been renowned for keeping a tight focus on design and sailing. This time ETNZ has had its fair share of preoccupations, from lockdown to a public storm alleging mishandling of public money (quashed following a government investigation).
The team dealt with this by placing CEO Grant Dalton in charge of the overall event and commercial management, with Shoebridge focussing on bringing together the sailing side.
“We realised pretty early that somehow you have got to separate the two and run independently. We are acting as if we were a challenger,” he says.
This Cup will feel very different: spectators can’t travel to New Zealand, the Youth America’s Cup has been cancelled, and the Superyacht Regatta will be a much diminished affair. But, says Shoebridge, “95% of the crowd that would be here will still come because they live here. It’s still going to look great and be huge.
“These boats are very challenging, very powerful. It is such an exciting time if you’re a sailor or a designer, trying to figure out how to get the most out of this revolutionary new boat. It has been [years of] constant working and in just over three-and-a-half months it will all be finished. But now, we are getting to the fun part.”
Mattew Sheahan, December 10, 2020