Auckland Analysis of the 36th America’s Cup

Sail News

In the next few weeks, Luna Rossa Prada Pirelli Team, the New York Yacht Club’s American Magic effort and INEOS Team UK will all battle in the Prada Cup Challenger Selection Series in Auckland to determine who will face the Defender, Emirates Team New Zealand (ETNZ), in the 36th America’s Cup match in March.

In San Francisco back in 2013 there were also three challengers, but it was pretty much a foregone conclusion the Kiwis would win the elimination series and face then Defender, Oracle Team USA. Luna Rossa had bought its design from the New Zealanders and clearly did not receive all the best refinements. Similarly, Sweden’s Artemis Racing had bet wrong on its design and did not have a competitive boat. The team also experienced the tragic death of Andrew Simpson during a training accident a mere three months before the start of racing.

This time, though, it’s a whole different situation.

All three challengers are strong, and calling the winner of the Prada Cup is anything but a sure bet. Challenger of Record, Luna Rossa Prada Pirelli, represents the sixth challenge by team owner, Patrizio Bertelli. The concept of its first boat was widely admired and thought by many observers to be the best of the first-generation AC75s. British challenger INEOS Team UK could also be tough. Skipper Ben Ainslie recruited Aussie sailor Grant Simmer—a veteran of the Aussie team that won the Cup from the New York Yacht Club in 1983 no less—as team CEO, and the effort is funded by the UK’s richest person, INEOS founder Jim Ratcliffe. Similarly, New York Yacht Club American Magic, as the team is officially called, not only has the support and tradition of the same club that started it all in 1851, but the backing of three billionaire club members: Hap Fauth, Doug DeVos and Roger Penske. Team leader Terry Hutchinson is also a formidable a sailor in his own right and leads a team that has spent more days on the water than anyone else, the Defender included.

The canting systems and foil arms are all “provided equipment” and uniform across the entire fleet

The star of the show for the 36th America’s Cup will be the AC75 yacht. The four teams have together spent something approaching half a billion dollars developing and learning to race these revolutionary foiling monohulls, and the results have been nothing less than spectacular. The Defenders from the Royal New Zealand Yacht Squadron demonstrated their daring and imagination when they first unveiled the AC75 concept back in November 2017 with a debut video showing 3D renderings of an improbable vessel. The designers obviously knew capsizes would be inevitable aboard a monohull with no keel and a mainsail carried on a mast towering 87ft above deck, but not to worry. The yachts would also be self-righting, by moving around the canting foil arms and their ballasted wings. The scythe-like wings themselves called to mind the chariot-race scene in Ben-Hur.

A little overly ambitious? A 75ft-long full-foiling monohull capable of highway speeds under sail but also capable of capsizing like a 470? Perhaps. But it works. Not only that, it works well.

All four teams have long-since figured out how to do foiling jibes and tacks. At this writing, ETNZ and American Magic have also both capsized in training, the Kiwis having gone over twice. Both teams were also able to resume sailing after getting their boats upright again, although they needed help from their chase boats to do so.

The Kiwi’s second boat features a “bustle” running well aft and distinct cockpits for the crew

The Kiwi’s second boat features a “bustle” running well aft and distinct cockpits for the crew

Team New Zealand’s second capsize was the more serious of the two, as the boat sustained damage and had to be towed back to base. Jimmy Spithill, now with Luna Rossa, says he expects all the teams will capsize at least once. The good news is the damage sustained by the New Zealand boat was a far cry from Spithill’s experience with Oracle Team USA’s AC72 catamaran on San Francisco Bay in 2012. On its ninth day of sailing, the team pitchpoled in front of the St. Francis Yacht Club after which the boat was washed five miles outside the Golden Gate by the tide, where the giant wingsail and much of the boat were destroyed by the rough seas. They lost four months of training while rebuilding both the boat and a new wing. Oracle’s plan for righting an AC72 appears to have been, “Don’t capsize.”

American Magic, the sole U.S. challenger in 2021, was the first team to demonstrate that the AC75 concept actually worked at full scale. Its first yacht, Defiant, flew the first day the team sailed it back in late 2019. The crew cast off lines, was towed out onto Narragansett Bay near American Magic’s home base of Bristol, Rhode Island, hoisted the double skin mainsail and went foiling. Maybe the crew was inspired by the maiden sail of Reliance, Nat Herreshoff’s 1903 defender and the largest yacht ever to compete in the America’s Cup. With Herreshoff at the helm, Reliance was also fully powered up and burying the rail the first time out.

The Brits’ second boat was vastly different, with a pronounced skeg running along much of the hull

The Brits’ second boat was vastly different, with a pronounced skeg running along much of the hull

With a radical, brand-new design rule, ETNZ and Luna Rossa had a several-month head start for their design work: they wrote the rule and, of course, knew what it would say well before it was published. The advantage was clear when the teams launched their boats. American Magic and INEOS both had scow-like hulls. But ETNZ’s hull sported a “bustle,” or narrow, slightly deeper portion of hull running along the bottom of the hull on centerline, and Luna Rossa was even more extreme, with a kind of blunt skeg running the length of its hull. In both cases, the bustle is intended to not only help the boats track when in displacement mode, but get the boats airborne more easily by providing a little extra buoyancy as they begin lifting clear. The bustles also help the boats soften the impact and get airborne again in the event they ever fall off their foils and enhance the “end-plate” effect of the hull by narrowing the space between it and the water. This in turn makes the sailplan more efficient by forcing the air to flow the length of the bottom portion of the sail, as opposed to slipping to underneath it.

INEOS Team UK’s first AC75 featured a gently curved bottom

INEOS Team UK’s first AC75 featured a gently curved bottom

Early on, American Magic’s strategy was to make a rapid first design and get it out on the water as quickly as the rules allowed—the end of March 2019—in an effort to learn as much as they could about AC75 sailing before designing their second boat. Unfortunately, that plan was derailed by a months-long delay in the delivery of the “supplied equipment” foil-cant system (FCS) and foil arms. ETNZ designed and built the hydraulically driven FCS used to raise and lower the foils, but didn’t deliver until the end of March. Luna Rossa designed the foil arms, but its first design failed to reach the target load level. (In addition to the lifting foils and arms, the masts are also identical across all the AC75s.) This pushed the launch of all four teams’ first boats to fall 2019.

We’ve now seen all the teams’ second boats—the ones they plan to race. American Magic and INEOS have both abandoned the scow form and added skegs. For its part, ETNZ evolved its round bustle into an even sharper skeg. The three teams seemed to confirm that Luna Rossa was on the right track. The Italians’ own test data must have confirmed their assumptions, too, as they made no dramatic changes.

The AC75 takes the foiling revolution in several new directions. Most obviously, it’s a monohull that flies on two legs, the leeward foil and rudder, since the windward foil is lifted clear of the water when the boats are underway. Less obvious are the foils themselves. The AC72 and AC50 catamarans used in the previous two Cups generated lift by raking the entire daggerboard fore and aft to change the angle of attack of its lifting surfaces. The reason for this was the rules forbade us of movable control surfaces. This time, though, the foil wings have movable flaps, like airplane wings, and the arms only raise and lower, with no rake adjustment. Also, while the catamarans relied on human grinders to pump the oil powering their hydraulics, on the AC75 batteries and electric pumps move the oil for the underwater control surfaces—raising and lowering the 1.2-ton foils, and controlling the flaps on the foil wings and the rake of the rudder. This is not to say there isn’t still been plenty of reason for teams’ grinders to hit the gym. Batteries may provide the energy for the boats’ underwater control surfaces, but humans provide the hydraulic power for everything else, including the AC75’s massive rig. In other words, there is still plenty oil that needs to be pushed around.


AC75 Specifications

LOA 75ft
LOA (hull) 67ft 11in
Bowsprit 6ft 7in
Beam (hull) 16ft
Weight 14,220lb (light ship)
Rudder Max Draft 11ft 6in
Rudder Max Span 9ft 11in
Foils max wingspan 13ft 2in
Mast Height (from deck) 86ft 11in
Mainsail 1,560ft2Jib 970ft2Code 0 2,152ft2Crew 11

In addition to these basic parameters, a number of the components going into an AC75 are “supplied” and therefore standardized across the fleet to help save design and construction costs. These include rigging, mast tubes, and the foil arms and canting systems. Hulls, sails, deck layouts and, of course, the all-important hydrofoils and super-secret hydraulic control systems and actuators belowdecks are up to the individual teams—may the best builders and designers win!

Another major difference with the catamarans: no rigid wing. We are back to soft sails. The mainsail has two skins, providing more control and less drag than a conventional sail. (See sidebar An Innovative New Main) The mast rotates, but the spreaders don’t—they are hinged. Logistics were part of the decision to abandon the wingsails of the last two Cups. Stepping the wing on an AC72, for example, took 45 people 90 minutes.

Interestingly, back in 1927, a patent for a double-skinned mainsail on a rotating D-shaped mast was issued to none other than L. Francis Herreshoff, son of Capt. Nathanael Herreshoff. Another designer from the early 20th century had an even simpler solution: Charles E. Nicholson used a “luff casing” made of sailcloth on the J-Class Shamrock IV’s mainsail in the 1920 match.

Like the wings on the catamarans of 2013 and 2017, the mainsails are end-plated to the deck to prevent air from flowing underneath them (an effect amplified by the boats’ bustles). This effectively increases the span, or luff length, of the main and decreases induced drag, i.e., the drag created when generating lift from the airfoil of the mast and main. Like the twin-skinned main, end-plating is not new. In 1967 Olin Stephens designed the 12-Metre Intrepid with the grinders belowdecks, so the boom could be as close to the deck as possible.

What about headsails? The rules require that each boat carry a jib and Code 0, but don’t expect many sail changes. The teams will decide what headsails to use in each of the 25-minute races and then carry weights to compensate for any sails they don’t have onboard. Code 0’s might be needed to get the boats up on their foils in light air, but don’t be surprised if we only see jibs. The teams have been testing Code 0’s, but may find that there is too much of a drag penalty once the boats get up to full speed on their foils to make them effective. Despite the fact there won’t be many sail changes, the crews will still have some work to do with their headsails: class rules require that a sailor unload a sheet from one winch and load a sheet onto another for each tack or jibe—no self-tacking allowed.

The crew of 11 must also all have the same “nationality” as the club it represents, and at least three of the 11 must be citizens of the country. Any crew who are not passport holders must have been in the country for at least 380 days in the two years that ended on August 31, 2020. They must also have established permanent, principal residency in the country. The rules add one more requirement: “There shall be 11 crewmembers, who shall all be human beings.” In other words, no cyborgs. That said, we’re talking about some pretty big human beings here, the crew weight limit having been increased to over 2,100lb. “Cyclors,” like those used by the Kiwis in 2017 are not allowed. The coffee grinders must be turned by hand.

It’s easy to overlook the importance of ergonomics, but it plays a key role. In 2013 ETNZ designed its AC72 with the grinding pedestals mounted transversely. To reduce drag they lowered the pedestals, and the grinders sat on the deck, losing efficiency. The Kiwis more than compensated in 2017 when they launched their second AC50 with its innovative cycling stations instead of grinding pedestals. Not only did these cyclors produce more power, they also left the sailors’ hands-free. Trimmer Blair Tuke, for example, used a joystick and a “follow the dot” display on a tablet to control the foils as he was riding his cylcor.

All four first-generation boats had the crew in trenches, mostly below deck level, well outboard to either side of the boom. All the challengers kept the trenches for their second boats. However, instead of trenches, the Kiwis are now ensconced in cockpits to either side of the hull, with a low portion of deck in between them. This allows the three crew who change sides—helmsman Pete Burling, mainsail trimmer Glenn Ashby, and Tuke, now officially a “flight controller”—to do so by running around the front of the mast. On the challengers’ boats, crew must all cross aft of the mainsail.

Control systems for the foil wings and the mainsail have absorbed countless engineering hours and lots of money. In early testing, the teams almost certainly had autopilots adjusting the foils and their mainsails as the crews worked on how best to replicate these same settings manually. However, that kind of automation is forbidden during racing. Of those early days, Freddie Carr, one of the British team’s grinders said, “When you leave the dock, your life is in the hands of the computers, and the guy who steers the boat… All the systems on the boat, except for the winches turning, depend on computers. You are then aware that you are now sailing on a boat that is based entirely on computer code. But I guess when you’re sitting in an aircraft at 40,000 feet, it’s exactly the same thing.”

So much for the technology. Now let’s take a look at what it will be like not only sailing but actually racing these boats.

The Prada Cup challenger-elimination series takes place in three stages between Jan. 15 and Feb. 22. The actual America’s Cup regatta begins March 6, first to seven wins. 

The Prada Cup challenger-elimination series takes place in three stages between Jan. 15 and Feb. 22. The actual America’s Cup regatta begins March 6, first to seven wins. 

There will be a number of courses to choose from, depending on the weather conditions

There will be a number of courses to choose from, depending on the weather conditions

First: flying is faster than floating. To win races you need to get up on your foils and stay there. This could be challenging in light air at the lower windspeed limit of 6.5 knots. Further complicating things is the fact that with no keel, the boats have very little righting moment in displacement mode. The trick is to bear away, sheeting on gradually until the boat gets up enough speed to foil. Once foiling, the boat develops a truly massive righting moment, with a fulcrum a little over 15ft outboard at the leeward foil wing. At this point, we get amazing speed. These are the fastest boats ever built sailing upwind—clocking speeds of over 30 knots. On other points of sail they have hit speeds of 50 knots and more. At these kinds of speeds the apparent wind angle is roughly the same upwind and down—approximately 15 degrees. The boats essentially never jibe. Everything is a tack. Travelling at 30 knots, the boats will reach the course boundary within about 40 seconds of crossing the starting line—not much time to plan your maneuvers!

In terms of the racecourse, in 2021 it features a return to upwind starts, is about 0.8 nautical miles wide and about 2 miles long. Races will last around 25 minutes. The warning signal is at three minutes. The preparatory signal, when the yachts may enter the starting box, is at two, with the boat entering on port allowed to enter 10 seconds before the boat entering on starboard.

For the start, the boats can be towed up onto their foils as long as they drop the tow before the warning signal. It will be interesting to see the tactics in the pre-starts. We will almost certainly not see the dial-ups or circling that non-foiling match racers engage in. High-speed timed runs to the line will probably be key, unless, of course, a boat decides to engage and try and force its opponent to lose speed and drop off its foils. While racing, if a boat gets a penalty, including OCS (“on course side,” or over early at the start) or going outside the course boundaries, the offending crew can offload it by falling a further 50 meters behind, or by losing 50 meters if the two boars are on different legs of the course.

Muscle power is still what “pushes the oil” to energize the hydraulic systems controlling the boats’ towering rigs

Muscle power is still what “pushes the oil” to energize the hydraulic systems controlling the boats’ towering rigs

Dropping off foils is likely to lose a race—the other boat still on its foils will simply speed away too quickly. In 2013 and 2017, a boat that capsized was also immediately disqualified, so that all the chase boats could immediately assist in rescuing the crew. Again, the AC75 capsizes to date have been relatively tame affairs. Not only that, but with the AC75 having been proclaimed as self-righting, a capsized boat may continue racing if it can right itself again without outside help. None of the teams has been practicing capsizes or recoveries, so it’s a safe bet a boat that capsizes will lose the race—unless, of course, the other boat capsizes as well…

The course will have gates at the windward and leeward ends. The “zone” in which the rules governing mark roundings come into effect is 70 meters from the mark. The rule for mark-room is different from the normal rules in that if the boats are overlapped when the first boat enters the zone, the inside boat automatically gets room. It doesn’t matter which boat got to the zone first, if one of them has right-of-way or if one of them has to tack to round the mark. The inside boat has rights. Elsewhere on the course, starboard tack has rights over port, and a boat to windward stays clear of a boat on the same tack to leeward. Within 90 meters of the course boundaries, a boat that is outside and overlapped or clear astern must give the other boat room to sail her proper courses. This includes room to tack or jibe. In other words, you can’t force the other boat out of bounds.

At press time, Cup fans were still waiting to see the AC75’s do some actual racing in December during the America’s Cup World Series regatta and Christmas Race, both in Auckland. Undoubtedly many unknowns will be answered then. At the same time, though one thing you can be sure of is that whatever was fast enough to win these early races will no longer be enough to win the actual America’s Cup. The Kiwis and all three challengers will undoubtedly continue developing both their boats and their tactics throughout the intervening months. Remember the way Oracle Team USA continued to up its game all through its epic “comeback” in 2013 on San Francisco Bay? Expect these same kinds of performance improvement in 2021. One way or the other, we are in for an exciting America’s Cup! 

An Innovative New Main

Amid all the hoopla surrounding the extraterrestrial-like appendages and hull forms of the America’s Cup’s AC75 monohulls, it’s been easy to forget about the other innovation waving around overhead—the boats’ twin-skinned mains, in which not one but two mainsails fly in parallel from twin tracks on either side of the trailing edge of a D-shaped spar creating a kind of “soft wing.”

According to North Sails’ director of design and engineering, JB Braun, whose company helped create the rules governing the sails, going with twin skins creates a 10-15 percent advantage in efficiency over a conventional soft main (at the same time it reduces the cost and complexity of a rigid wing). The reason for this, he says, is because it eliminates the turbulence created where the sail attaches to the mast. As an added benefit, Braun says, the new soft wings are appreciably lighter than a rigid wing, an important factor when getting a foiling boat airborne.

Key to figuring out how best to spec the new sails, Braun says, was the use North Sail’s proprietary Fluid-Structure-Interaction (FSI) modeling tools, which North modified in order to allow designers and rules-makers to see how the sails would work in the real world (in much the same North Sails worked with designers and rules-makers for the AC72s and AC50s used in the 34th and 35th America’s Cups). The resulting sails, though, are anything but one-design, with plenty of room in the rule for innovations. Specifically, Braun says, the D-section mast and certain parameters, like the basic dimensions of the sails are fixed. However, with respect to materials, batten placement, camber and the means by which the sails are impacted by a pair of control arms located at the head and foot of the sails, anything goes. Same thing with the mechanics of each boat’s mainsheet, traveler and other hydraulically operated sail controls.

For the record, North is building the sails for the Emirates Team New Zealand, INEO Team UK and Prada; Quantum is building the sails for American Magic—no great surprise given the fact Quantum Sails owner Doug DeVos, is one of the team principals.

In terms of their operation, the sails are attached via conventional boltropes to grooves on either side of the mast’s D-section, with each skin hoisted in much the same as a conventional soft main. Interestingly, the two leeches are not attached, for the simple reason that with each tack or jibe, the mast pulls the leeward luff forward as it rotates, which pulls the body and leech of the sail forward as well. According to Braun, the rules allow the leeches to be “laced” together in the area of the battens. But that’s about it.

Ed Note: A leading authority on the America’s Cup, Jack Griffin is a widely published journalist and author of the book Turning the Tide, which provides the definitive account of Oracle Team USA’s “comeback” in the 2013 America’s Cup. He is also a former brand manager for the Alinghi America’s Cup team and a member of the America’s Cup Hall of Fame selection committee. In 2010 he created the web site Cup Experience ( and has more recently created the site “Cup Experience Club,” (, offering the latest inside scoop on all things America’s Cup

Get the Details

The 36th America’s Cup

The Teams of the 36th America’s Cup

January 2021

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