In this month's America's Cup sailing race, the competing vessels will barely skim the surface of the ocean while reaching speeds unthinkable even a few years ago. They hardly resemble sailboats at all. At what point does technology change a sport to something different entirely?

Graeme Spence didn't have time to contemplate why, exactly, he had just fallen off his very fast boat. He hadn't been able to study the failures that had launched him into Bermuda's Great Sound on an otherwise routine training day in February, his hands still stretching desperately for the hold ripped out of his reach. He had a deep understanding of the gravity of his situation, but not the sort of understanding that allows for remedy. Spence was the first man to go over the front of the sailing vessel USA 17, Oracle Team USA's entry in this summer's edition of the America's Cup, less a boat than a collection of knives racing over the water. Whether Spence would also become the first man to survive the trip under 17 wasn't really up to him.

"By the time I realized I wasn't in the right place at the right time . . ." he says.

Calling 17 a sailboat is like calling the stealth bomber a plane. It's not inaccurate, but the picture it makes is incomplete. Waning are the days of billowing spinnakers and yachtsmen in striped ties and blue blazers. Today's boats are anti-romantics. They are stripped-down engineering solutions to hydrodynamic problems, and they're crewed by athletes better judged by their strength and reaction times than their readings of the wind. Not much can keep up with a modern racing yacht, and that sometimes includes the men who sail them.

17 is that sinister-looking class of boat known as a foiling catamaran. It has twin carbon-fiber hulls, sleek and black, connected by a pair of beams with fairings that look like spoilers. There is no teak in sight. There is, however, a futuristic-seeming pod that serves as its spine, supporting the towering wing it has in place of a sail. Never mind a sheet of canvas flapping in the breeze; 17 is driven by a stiff, laser-precise assembly of Nomex, carbon-fiber, and Clysar. That wing is so efficient, and the boat is so light— fifty-three hundred pounds, including its hulking six-man crew—it floats on the surface of the water only at rest, which is almost physically impossible for it to take. At speed, it has no draft. 17 flies, riding sometimes several feet above the waves on top of four thin foils. Usually, only one of the two larger foils at the front (called daggerboards or L-foils, because of their distinctive shape) is in the water. The other is raised clear to reduce drag. The smaller two at the back (rudders with T-foils) are almost always both in the water, unless something has gone wrong.

A lot of things had gone wrong when Spence went overboard. After, Oracle Team USA's forensics team would analyze the gut-churning moment using their continuous streams of onboard data and camera footage. "I hope we never see that again," Christoph Erbelding, a German aeronautics expert and the boat's wing designer, says today. "Falling off the front is really bad."

This year's 17 is still a boat, because it can float. But for the first time in sailing's long history, it will be a mistake if it does.

Like accident investigators, the team reconstructed the "cascade of events" that led to Spence's slipping under a machine that might hit an incredible fifty knots. (The Swiss winner of the 2007 America's Cup, the more traditional single-hulled Alinghi, topped out at about 15 knots.) Sailors who fall over the front of a foiling catamaran have the significant misfortune of finding themselves in the path of its blade-sharp foils. Together, 17's boards make for just fifty square feet of wetted surface. But when you just have to hope that none of them hits you, "that's a lot of real estate in the water," Erbelding says.

Three months until the race: Sailors from Team USA exit the wing shed, where 17's massive "sail" is stored. River Jordan

In 2015, Franck Cammas, a veteran America's Cup skipper, went over the side of his smaller, slower foiling catamaran during a training sail and was struck by one of the rudders. His right foot was nearly severed. The front-falling Spence would have to contend with the daggerboard, too.

The boat had been in the water for only a few days, its crew just getting to know it. They had watched it get pulled out of its boat shed, shining in the sun, and craned into place at Bermuda's historic Royal Naval Dockyard. The wing is kept in its own pristine hangar, and it too needed the crane to be mounted into place. Old stone warehouses, former ruins made new again, were the only nearby reminders of less ruthlessly efficient days. They provided the sun-bleached backdrop for 17's striking black mass.

After being escorted past the breakwater, the boat's Australian skipper, Jimmy Spithill—he became a licensed pilot to help him better contend with this new breed of vessel—took one of the distinctive red wheels. It has several twist grips, designed with help from BMW, to control the height and attitude of the L-foils. A stick had also been tried, but it proved too tough to hold in the wind and chop. Sometimes old sailing technology is the right technology, and even the most modern ships are best steered with wheels.

Spence was one of the four grinders on board. With their enormous arms—Spence, also an Australian, is built like a rugby player—the grinders spin winches "like hamsters on a wheel," he says, to generate hydraulic pressure. That pressurized oil provides the energy to do things like move the daggerboards or shape the wing.

Sailors remove salt from the hulls after every practice. River Jordan

The boat buffeted across the sound, its crew trying to divine the secrets of their new charge. Just before Spence fell, Spithill was struggling to reduce the daggerboard's angle of attack. It was pitched like an aileron at takeoff so that the boat could take its version of flight. This time, there wasn't enough pressure in the hydraulic system for Spithill to level the daggerboard after he reached his desired altitude. He couldn't flatten things out. Either the system wasn't efficient enough or the grinders had not been grinding enough, or both. The daggerboard stayed dialed back. Which meant the boat continued to climb until it exited the water, foils and all. It went airborne.

Although 17 can seem as much plane as boat, full flight is, in the words of Andrew Campbell, another sailor on board that day, "very momentary." Water provides much more lift than air, and 17's daggerboards are sufficient to steady it when submerged. In the sky, not so much. The boat crashed back into the water. 17's speed never makes a greater impression, particularly to its occupants, than when it hits something. "Man, you understand really quick how fast you're going," Campbell says. He clattered into a crewmate and was happy for his helmet. Spence, who had been bounding across the net stretched between the hulls, was tossed forward into the sea.

He splashed into the crystal-blue water between 17's leeward hull and its central pod. The two beams loomed above him.

The daggerboard knifed just below him. Then the rudder somehow did as well.

Spence popped out of the froth behind the boat, looking as though he had seen something he would never forget. Unlike Franck Cammas, he still had his four appendages fully attached.

Like 17, he is also still given to fly.

During races Team USA's grinders tuck into 17's hollow hulls to spin winches, which provide the hydraulic power to raise and lower the L-foils, shown above. Though 17 has two L-foils (one on each hull) it usually flies on only one, with the other raised i Alex Pang

The America's Cup is the oldest trophy in international sports. The "Auld Mug" is an elaborate silver ewer that was first won in 1851 by the schooner America in a race around the Isle of Wight. The syndicate that owned America named the trophy after its winning ship and wrote a set of rules called the Deed of Gift, meant to ensure that the America's Cup remained an object of perpetual pursuit by sailors in fast boats. This year's edition will mark the thirty-fifth time the defender of the title has been raced by a challenger.

Oracle Team USA—which has been funded by Oracle founder Larry Ellison since 2000 and represents the Golden Gate Yacht Club—is the current holder of the trophy. Rivals from New Zealand, Sweden, Japan, Britain, and France began racing against each other in late May to determine who will compete in the best-of-thirteen final against the Americans this month.

Most of the time, the defender and the challengers agree on the class and size of the yachts they are going to race. (Usually races must take place within ten months of an accepted challenge.) This year, all six boats have identical fifty-foot hulls, and the wings are all the same size and shape—only the foils, fairings, and hydraulic and electric control systems differ. Their specifics are closely guarded secrets, but from any sort of distance, the 2017 boats are indistinguishable from one another. Three or four of them might take to the sound for practice at the same time, and were it not for the flags on their wings, they could be confused for a colony of bats, identical down to their alien midflight corrections.

On less fair-minded occasions when no such class agreement can be reached, the competition reverts to the parameters outlined in the Deed of Gift: Yachts no more than ninety feet long and ninety feet wide shall race in salt water. That's what happened in 2010, when it was decided that the Alinghi's Swiss defenders would face the Golden Gate Yacht Club, with each team racing whatever sort of sailboat it wanted. It just couldn't be longer or wider than ninety feet.

Team USA Coach Philippe Presti reviews film of practice at the team's facility in Bermuda. River Jordan

Ellison, who had already mounted two unsuccessful challenges, also made a judgment of his own: This time, he was going to win.

For that race, he financed what remains one of the most ambitious boats ever built, the sort of miracle that comes when bored billionaires decide to do something insane. The Deed of Gift was written at a time when only the size of the boat mattered, because it's always been held that the bigger the boat, the faster it sails. But instructing modern boat designers that they need only confine themselves to a square that measures ninety feet by ninety feet—and giving them a budget far more limitless—made possible some new kind of monster.

All of Ellison's boats are named 17. The 2010 iteration was a massive trimaran with a wing instead of a sail. That wing happened to be the single largest one ever constructed, for plane or ship. Topping out at 223 feet, the Golden Gate Yacht Club's entry could not sail under its namesake bridge. The Swiss showed up for the race with a catamaran, because multihulls are faster than bottom-heavy monohull yachts. (The game, although now taken to extremes, has always been about increasing lift and reducing drag.)

Regrettably for the Swiss, they also showed up with an old-fashioned sail.

America: The namesake and first winner of the America's Cup, circa 1851, was a schooner owned by the New York Yacht Club. Its top speed was about 11 knots.

For a sport that prides itself on its heritage, nothing would ever be the same. Three years later, the best sailors in the world still struggled to harness the fearsome capabilities of their boats. The protocol for the 2013 America's Cup mandated that seventy-two-foot winged catamarans would face off in Ellison's home port of San Francisco. They were foiled, but design and race rules were written with the expectation that the boats would stay boats—a kind of self-imposed governor meant to restore sanity to the proceedings. Ian Burns, Oracle Team USA's director of performance, helped write those guidelines. "We put in a bunch of rules that we thought would make it relatively impossible to fly," he says.

Team New Zealand had other ideas.

Sailing has always been a sport won on its edges. Sometimes that edge is gained during the ingenuity race that precedes the actual competition. More often it's found by the brave pioneers charged with sailing these unpredictable machines. In 2013, the Kiwis looked at their boat, and they looked at the rules that bound them, and they still found a way to fly.

Like those who fought to conquer the skies before them, the first generation of flying sailors suffered for their progress. Winged multihulled boats are fast, but their lack of a keel makes them easy to tip. Spithill pitch-poled that year's 17 during its early trials, heavily damaging it after only eight days on the water. The Swedish team's entry also capsized, leading to the death of a crew member.

"I can't wait for my kids to be giving me shit in ten years, saying 'What were you doing in those old foiling boats out there?'"

But the Kiwis remained committed, and the hosts soon found themselves behind in the best-of-seventeen final eight heats to one. At first they could only watch as their rivals flew downwind—even through jibes, when a boat turns away from the wind instead of into it and speed drops considerably. Oracle Team USA spied and studied and practiced, trying to crack the Kiwi code. "Until you really get pushed by the best, that's what raises the development curve," Spithill says. The Americans eventually found their downwind wings, and they also kept aloft during jibes. Then, just when one more loss would have cost them the trophy, they managed to do the unthinkable: They flew upwind, too.

Only foiling tacks defied them. They won eight straight races to come back and retain the cup, gliding around the course at over thirty knots, stunning Team New Zealand and the wider sailing community. Grant Simmer, Oracle Team USA's chief operating officer then and now, still marvels at the memory. "We didn't go into the Cup thinking we were going to foil upwind, no way," he says. "Since then, we just foil everywhere."

Including tacks?

He nods. "We can do a dry race now," he says. As in, the hulls never touch the water. This year's 17 is still a boat, because it can float. But for the first time in sailing's long history, it will be a mistake if it does.

When 17 takes full flight, its daggerboard (black) and rudders (red) are in full view. River Jordan

After decades of incremental change—after it took 2007's Alinghi far longer than a century to grind out what would have amounted to a four-knot advantage over 1851's America—it has taken only the last ten years to fly more than three times as fast. What was considered the height of racing design only a decade ago is now almost laughably obsolete. "Cleopatra going down the Nile was going roughly the same speed using roughly the same technology," Ian Burns says. "You look at where we've come since 2007, it's bigger than a revolution." Remember the bigger the boat, the faster it is? "That law's been completely broken," he says. This year's fifty-foot entries would whip the seventy-two-footers from 2013.

Nobody knows what's possible for a boat that's powered by muscle and wind anymore. As it waits in its shed for another experimental run, today's 17 remains an enigma even to the people who made it. Builder Mark Turner puts its number of custom parts in the high hundreds. Because they're too expensive to test for failure—a set of daggerboards costs about $300,000 and takes eight weeks to make in distant New Zealand—each component harbors its own set of tiny mysteries. "You're sort of on the edge the whole time," Turner says. That's why 17's designers and builders often refer to it as a "thing" rather than a "boat," as though they won't know what it can do until it does it.

"It's a pretty crazy thing, actually," Erbelding says, looking at drawings of his dreams. Asked what 17's top speed might be, the genial German smiles and shakes his head. "I can't tell you," he says. "We don't know."

Though high-tech, 17 still requires brute force to sail. River Jordan

By this past March, 17's crew had pushed well beyond the envelope suggested by pre-build simulations, and they still had nearly three more months to master sailing it. They reported to Team USA's sprawling base like soldiers, usually starting their twelve-hour days in their top-end gym, complete with a boxing ring and big plastic buckets for when they throw up. Then they get on their safety gear, looking like fighter pilots who also plan on taking a dip, sailing the boat as often as six times a week, chased across the sound by opposition spies with 1,000-hp motors, their wakes like vapor trails on the water.

Each day the crew pushes a little faster, a little farther, waiting for frantic calls from someone like Erbelding, monitoring wing loads on his laptop back on shore. The association with Oracle comes in especially handy there. So far, everything's held up with the exception of a single daggerboard that couldn't take the strain. Speed normally compromises a boat's ability to turn, but 17 has proved nimble. Foiling tacks, the most elusive of goals only four years ago, still aren't easy—they require a precisely choreographed dance between the six men on board and their boat—but they are closer to routine. Watching 17 tear across the sound is like watching a rocket that hasn't quite hit escape velocity but will. It doesn't whistle past. It screams.

On increasing occasion, the boat moves so fast through the water that it effectively begins boiling it, an unlikely seeming phenomenon called cavitation. "We've come up against a different kind of wall," Andrew Campbell says. When the foils slice through the water—and thankfully not through Graeme Spence—the pressure on top of them can drop so much the water starts to bubble, the way soda starts to fizz when the cap is taken off. But the bubbles aren't air. They're steam, which leads to crippling drag and loss of lift. Although 17's relationship with the ocean is minimal, how to stop cooking it has become one of Team USA's more otherworldly concerns.

Making the foils smaller isn't really an option. "As soon as you wipe out once, it's not worth that extra bit of speed," Campbell says. Unlike traditional yachts, foiling catamarans aren't meant to lean in the wind, which is one of the harder adjustments to make in watching them. Much more than a 15-degree swing off vertical usually spells disaster. In ideal conditions, these boats stand bolt upright, leaving them looking even more imperious than they can already seem. It takes time to understand that the weakness of 17, and so the even greater possibility of it, is under the surface.

Maybe the foils should have slots like an airplane's wing—like the wing that powers 17—widest at takeoff and made slender in flight. Maybe the shape of the L-foil is wrong—it's really the only shape that's been tried—and an O-foil or an F-foil or a W-foil will prove superior. Maybe the algorithms that are hunting through bottomless files of telemetry data will stumble upon some speed equation that the human brain can't parse. Maybe the control systems, much finer than they were only a few years ago, will be made better still, allowing for some small adjustment that opens a door no one even knows exists. Maybe the sailors themselves will wake up in the night and realize that if they only did this, they could fly even higher.

Jimmy Spithill smiles, thinking about the possibilities. "I can't wait for my kids to be giving me shit in ten years, saying 'What were you doing in those old foiling boats out there? What were you guys thinking?' I reckon there's going to be another big step," he says.

"There's still a lot to be learned. Who knows what will be the next big breakthrough? There are a lot of smart people in the world."

Auld Mug: The actual "cup" awarded to the winner of the America's Cup since the race's founding in 1851.

Christoph Erbelding is one of those smart people. He looks at 17 and feels something like love. He understands why others might not. "It's a different animal completely," he says. It's not beautiful, and it will more likely kill someone than rock anybody to sleep. The new class of purists created by its arrival will no doubt resent its coldness. But it's also a remarkable demonstration of invention, the winner of exponential gains in a sport and world that defies them. 17 is almost a new kind of vehicle that grants us a new kind of passage: the ability to travel faster than the wind that drives us.

"We're not touching down ever again," Erbelding says, and the way he says it, he makes you confuse sailing with soaring and mistake water for air. He makes you look at fish and see birds.

Update, June 26: The New Zealand team claimed the 35th America's Cup today by defeating Oracle Team USA in the final 7-1.

This story appears in the June 2017 issue.