SailGP: New T-Foils are tested in the birthplace of the big cat foiling concept

by Richard Gladwell/Sail-World.com/nz 15 Jan 14:48 PST

It is perhaps ironic that the test sailing of the new T-Foils to be used in the rest of SailGP Season 5 is taking place in the same location, on Auckland’s Hauraki Gulf, where an AC72 first foiled in September 2012.

Emirates Team New Zealand’s initiative in getting a 72ft wingsailed catamaran to foil triggered a new era in high performance sailing.

The lightning strike in the Kiwi design team resulted in the birth of the "L" foil - chosen not because of its brilliance from a performance perspective, but because it was the only way foils could fall within the ambit of the America's Cup Class rules.

The development was taken to the International Jury for the 2013 America’s Cup by Oracle Racing, and ruled to be within the constraints, if not contemplation, of the then AC72 Class Rule. Without the overall beam constraint, it is likely that the AC72 would have been fitted with the more commonplace T-Foil - so named because it resembles an inverted letter "T".

The ruling triggered a frantic scramble amongst then other Challengers and Defender to come up with a solution. Oracle and Artemis Racing (SWE) designed their own. A late entry, Luna Rossa (ITA) got out their chequebook and purchased a design package from the Kiwis.

Both the Italian and Kiwi teams worked up against each other off Takapuna Beach, where the so far 11 teams have been training in F50s since Monday. Using the same naming logic as the T-Foils, the initial set of foils on the New Zealand design became known as L-foils.

The L-foils were inward facing because of a class rule that read “The overall beam of the AC72 Yacht, in measurement condition and with all components in the position that yields the maximum beam measurement, shall not exceed 14.000 m. Appendages, in any and all positions, shall not exceed the maximum permitted overall beam.”

A feature of the L-foils was their long overhanging tip which extended well under the boat - and were very challenging for the structural designers, venturing into an area of unknown loadings. Oracle Racing broke one of their L-Foils on their first sail in San Francisco. - which hurt, given the teams were limited as to the number of foils they could build.

Despite the failure teams in the 2013 America’s Cup sailed with L foils, at the end of the longest regatta in America's Cup history, Oracle racing won because they were able to tweak their foiling package and sailing technique to be able to foil upwind.

The concept and learning was carried over into the Oracle Racing developed, near one-design AC50, they'd used so successfully in the 2017 America’s Cup in Bermuda. The L-Foil was ditched six years ago, in favour of the T-Foil, as soon as Emirates Team NZ won the America's Cup in Bermuda and the AC75 foiling monohull became the new America's Cup class.

The fleet of AC50s used in that Cup formed the nucleus of the six team F50 fleet that launched SailGP five years ago.

While the L-Foils performed to expectations, their basic concept remained a response to a foible of the AC75 class rule - and given a more open and collaborative design and development – a complete anathema in the shark eat shark world of the America’s Cup design – then the T-foil may well have been adopted from the get-go.

For all their adept compliance with the AC72 and AC50 class rule, the L-foils were impractical, despite holding the bragging rights in the F50 vs AC75 speed contest.

Fast forward into 2024, the F50 and its L-foils have recorded the fastest speed in racing - when the records are compared with the AC75.

The Canadian SailGP team clocked a top speed of 101.98 km/h (55.1kts) during tests in San Francisco in 2004. The racing record was set by France during Season 3’s visit to Saint-Tropez, where the team hit a top speed of 99.94km/h (53.7kts). The fastest by an AC75 is 53.4kts, set in a bear-away turn by American Magic, off Bean Rock in the Waitemata harbour in Race 1 of the Semi-Finals of the 2021 Americas Cup. The mark was not extended in Barcelona in the 2024 Cup.

But we digress, for reasons which are not entirely clear, the L-foils were continued into the largely one design AC50 class - that even required all jibs to be from a single manufacturer, the foils were free design. The move was described away at the time as "leaving the designers something to play with".

In the 2017 Cup, all teams carried two L-foils one with more surface area for lift in light airs, and a slimmed down "All Purpose" (AP) with less drag and more speed in fresh breezes.

As is their want, Emirates Team New Zealand pushed the design and construction tolerances to the limit with the development of a long, light air, high lift foil that performed well beyond its intended wind range – with the downside that it developed a crack requiring ultrasound after every use. But it won the Cup for the Kiwis - and the L-foils two-cycle life was ditched for America's Cup competition.

While the controlled narrative would have it that the new T-Foils are all about improved speed and performance, from a practical perspective it is a surprise that the replacement of the archaic L-foil has taken SailGP so long.

We haven’t had a close look at the new foils, which are milled from titanium in two parts, instead of the L-Foils single piece carbon plank, which took three months to build. From photos the T-Foils appear to be a very elegant, and practical piece of design and construction. They should overcome many if not all of the issues with their 12yr old predecessor.

The T-foil consists of two basic parts, the mast which extends below the F50 and the wing foil itself – with the two socketed together. The T-Foil is the same basic foil concept as the AC75, the foiling monohull also developed by Emirates Team NZ, but the SailGP designed F50 version has been adapted to operate within the same centre case mechanism as the old L-foils.

Perhaps the most impressive aspect of the whole exercise is that the F50s could have been sailing in Dubai a month ago with L Foils, and now they are sailing in Auckland with a completely different foil type - real tribute to the skill and expertise of the SailGP design and engineering team

As happened with ETNZ's foiling AC75 off Takapuna, in September 2012, this week the SailGP crews have been feeling their way with the new foils. They’re into the virgin territory of live testing at 50kts!

The first day was a baptism by fire in winds recorded at over 30kts average and gusting to 33kts.

SailGP NZ’s wing trimmer, Blair Tuke told Sail-World on Wednesday morning that their first sail with the T-Foils was a four hour stint on Monday.

“Before that, about a year ago in Dubai, the whole SailGP team did a couple of hours with a T-Foil prototype, but was pretty light wind, and the foils were slightly different at that stage.”

“They've reduced in area since the initial testing,” he added.

Tuke says the surface area of the T-foils “is very similar, if not smaller, than the old foils, but obviously it's shared across both sides of the T-junction.”

Making a comparison of the old with the new, Tuke says “these ones are set up more for higher speed, lower aspect, but higher cavitation speed - that's probably the main difference.”

Cavitation is the sound barrier of the foiling world, occurring when a low pressure area develops on the board, causing the water to boil and break down surface flows. Typically it will occur at high speeds, and foil designers strive to improve their designs so the upper speed limit is as high as possible.

Tuke gives the new T-foils a big tick in this regard, explaining that despite hitting 52.5kts (or 97.2kmph in the speed parlance so beloved by SailGP), they haven’t experienced any cavitation. “Not on the T-foils, it’s on the rudders, because the rudders are still the old version rudder, and so they're still pretty close to cavitating," he explains.

“But to be honest, Monday was just Day 1, and we were just trying to hold on, really. As we do more and more, we’ll get more comfy and learn where the limits are.”

Martine Grael, Mubadala Brazil skipper described Monday’s sailing as “spicy.” As one of the newest team in the SailGP League they were wary about pushing the F50 to the limits in condition that were close to the top end for racing.

“We got some really strong gusts and very high speeds,” she explained.

“At the end of the day, we're just like trying to keep it real simple and just do everything, right.”

Performance-wise the double Olympic Gold medalist and Round the World racer says that there are a lot of similarities to the old foils.

“Some things have changed a little bit from the other foils, and we're just trying to figure out, for example what's the best way to turn."

“With this big breeze yesterday, there's a lot of things we haven't gone through as a team, so we're just trying to keep it easy at the same time."

“We were also cautious of not ruining the boat on the first day so yesterday was definitely percentage sailing and keeping a little bit safe.”

“Maybe I wanted to try to push a little bit more,” she mused, perhaps thinking back to some hard days in the Southern Ocean leg of the Volvo Ocean Race.

Without the five year history of the established SailGP teams, Mubadala Brazil need to take a different approach, and as well as Grael, and her brother Marco - a 49er Olympian - they have hired top 2024 America's Cup sailors Andy Maloney (NZL) and Leigh McMillan (GBR) for the sailing crew. Also joining the crew as a coach is Paul Goodison (USA) skipper of the American Magic 2024 program, and a key member of the afterguard in the 2021 America's Cup in Auckland. For all, both the 2021 and 2024 America's Cups were sailed in T-foiling AC75s - there is plenty of knowledge to be transferred to the new team.

The Graels are the Royal Family of Sailing in Brazil, and highly respected internationally. Father Torben ("Turbine") has five Olympic medals, to his credit, as well as two Round the World races - including one win, and several America's Cup campaigns with the Italian Luna Rossa team. Martine Grael says she has not discussed the new foils with her father "it's a lot different from keel boats I would imagine.

"I've been doing 49er sailing," she says in a big understatement - sailing in the 2016, 2020 and 2024 Olympics winning two Gold medals. "They are also very unstable boats. And I think that has helped me a lot with coming into these faster boats."

She says she will be drawing on Torben Grael's local knowledge when SailGP races in the 2016 Olympic venue, later this year. As well she will be drawing on the experience of her uncle Lars, a top catamaran sailor and double Olympic bronze medalist. With those layers of experience to draw on, Mubadala Brazil need to take a different approach, having been thrown in at the deep end, to quickly come up to the racing level of other SailGP teams - let alone finding the edges in sailing technique with the new T-Foils.

Three times America's Cup winner, and triple Olympic medalist in the 49er class, Peter Burling (NZL) now in their fourth SailGP season says “it's hard to really tell what the main differences are between the two foils.”

“Its a long time since we've sailed with the old foils, and we never really got to sail one type against the other," explains the Block Foils skipper.

“The whole fleet is obviously going switch over to the T's this weekend, and it's just about figuring out how to use those and how to get the most out of them.”

“We had awesome day out there on Monday. We were on the highest speed configuration we get on these boats, with the 18metre wing and the new foils. It would have been nice to be a little bit steadier a little bit lighter, just to get a bit more in tune with the boat before you having to push on those high wind strength training."

“But that's SailGP - when you get a moment out there, you got to make the most of it.”

“Our top speed yesterday was 97.2kmh (52.5kts) - something like that. We probably got over the 95kmh (50kts) mark about 10 times during the day, but it seemed pretty hard to push through from there. It's pretty cool to see how much the boats have changed, he added.

The top speeds were recorded through the bearway, turning downwind - sailing through the so-called "Valley of Death" as the foilers rapidly accelerate in response to their suddenly changed wind angle.

“They really accelerate. We expected the new foils to be a little bit quicker. The acceleration is steeper, but we did some good bear ways."

“On Monday we didn't quite make the “hundie” (100kmh), but we got pretty close, quite a few times off Takapuna."

“You'll see it happen this weekend. The forecast is for plenty of wind from the east, so you're going to see teams pushing right up to that sort of speed.”

At the other end of the wind scale, the crews did not have any real answers as to how the new foils would work in light winds - where like all foilers, the F50s are prone to not being able to pop out of the water, and fly or not being able to sail a deep angle to reach a mark.

“Compared to the HSB (High Speed Boards), the T-Foils seem to have a little bit more lift - it's just the way that the lift is distributed across the foil."

Regardless of the breeze on the racing sessions, even if the wind did go against the forecast and turn light, Blair Tuke doesn't expect to see the foils changed back to he old light air - high lift L-Foils.

“I'm not the one that makes that decision, so we'll just wait and see.”

That last comment touches on the other big advantage of the new T-foils aside from a speed and cavitation gains, is their versatility. The data from the last few days where winds have been light, moderate and heavy will highlight the performance edges of the new foils, which coupled with the three sizes of rig available means that racing will almost certainly take place, almost regardless of windstrength.

That degree of certainty is the big advantage of the new T-foils for the TV viewer and spectators.