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World’s Fastest Sailboat: Quantum Leap

Tech Review: How did Paul Larsen's Vestas Sailrocket 2 peg 64 knots? James Boyd explores the turbulent path to the recent record blitz.

June 18, 2013
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Vestas SailRocket 2

Vestas SailRocket 2

It looks nothing like the boats most of us sail, but the Vestas SailRocket 2 is the product of 50 years of sailing ingenuity and development. ›› The wing and the foil are aligned so as to perfectly offset the center of effort and the center of resistance. ›› The main pod is angled 20 degrees off centerline to match the apparent wind angle. ›› An aft rudder arrangement made the first Vestas SailRocket difficult to control. On SailRocket 2, the rudder is mounted on the forward pod. ›› Skipper Paul Larsen uses an automotive-style steering wheel to drive the boat. From the cockpit, he can control the wing and the depth of the foil, among other things. Mark Lloyd

Last November, in southwest Africa, a landmark moment occurred in the history of sailing when Paul Larsen pegged the outright world sailing speed record. In recent years the record was eclipsed in small increments, usually a fraction of a knot, but the Australian’s innovative Vestas SailRocket 2 flew down the 500-meter course at an average speed just over 75 mph, almost 10 knots faster than the previous record held by American kiteboarder Rob Douglas.

Tim Colman’s asymmetric Crossbow established the first 500-meter record in 1972 with a heady 26.3 knots. Windsurfers took hold of the record in 1986 and held it until 1993 when Simon McKeon’s asymmetric yacht Yellow Pages took it and held it until 2004. Windsurfers reigned again for a few years, but it was the kiteboarders who shattered the mythical 50-knot barrier in 2008. In 2009 Alain Thebault’s foiler L’Hydroptère managed 51.36 knots. But the kiteboarders quickly won it back when Douglas pushed the record to 55.65 knots.

With the latest record Larsen not only reclaimed it on behalf of “the boats,” but set a benchmark—65.45 knots to be precise—that will be hard to surpass.

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Despite the stunning margin of increase, the record did not come easily. The feat was the culmination of 10 years of hard graft, fiscal uncertainty, and severe setbacks.

The Australian-born Larsen had been best known in the sailing world for his offshore adventures. He crewed on Pete Goss’s ill-fated Team Philips, then ended up sailing around the world in The Race with Tony Bullimore. He completed another lap aboard Doha 2006, winner of the Oryx Quest.

In 2002, he and his Swedish girlfriend, Helena Darvelid, herself an accomplished offshore sailor, teamed up with English naval architect and speed sailing junkie Malcolm Barnsley.

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The catalyst for the SailRocket project was the book The 40-knot Sailboat written in 1963 by American rocket scientist and yacht design visionary Bernard Smith. At a time when yachts still had long keels, Smith described the idea of a sailing vessel dubbed the “aero-hydrofoil” with neutral stability: where the heeling moment from the rig is completely offset by a foil located to windward. Smith built models to prove his concept, but it was only when the first Vestas SailRocket was launched in the spring of 2004 that his concept was proven at full scale.

Initial progress was slow. In 2005, after two seasons getting to know the platform, they replaced its softsail rig with a wing. The first trials with the boat were on Portland Harbour, close to Larsen and Darvelid’s home in Weymouth, Great Britain. In 2007, the duo decamped to Walvis Bay, Namibia, a venue with perfect characteristics that offered more opportunity to carry out runs: a gently sloping beach, regular winds, and a 1,000-meter stretch of obstruction-free water. In recent years, Namibia has taken over from The French Trench in Saintes Maries de la Mer, France, as the preferred location for breaking sailing speed records. All the speed records set by kiteboarders were done in Luderitz, Namibia, some 250 miles south of Walvis Bay.

The first big speeds came in 2007, with SailRocket hitting an instantaneous speed of 42.4 knots during one run. It was well short of the record at the time, but fast enough to prove Smith’s concept. That number also enabled Larsen and Darvelid to gain vital sponsorship from wind turbine manufacturer Vestas.

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With such a groundbreaking boat, teething problems were inevitable. They were getting faster, but the boat, rather than the pilot, was still mostly in control. A significant issue was the steering. “The back of the boat looked like Edward Scissorhands,” says Larsen. “We had three rudders hanging off the back; one system was confusing the other. It was a mess.”

After nearly destroying the boat in a crash, Larsen and Darvelid, along with Barnsley and engineer George Dadd, set out to create a better steering system. With this fitted, and_ Vestas SailRocket_ rebuilt, they set off again, as Larsen says “on one of the wildest runs I’ve ever had in that boat.” The steering was better—the boat would bear away to some degree—but far from perfect. On one run, Vestas SailRocket ran onto the beach at 35 knots.

But despite the troubles controlling the boat, Larsen knew they were on the right track. After tweaking the rudder over the next few days, they did one run, in big winds and relatively rough conditions, where Larsen felt for the first time that he was in control of the beast. It was a landmark moment.

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“After that run, we booked the WSSRC for the first time,” he says, referring to the World Speed Sailing Record Council, which administers and validates all sailing speed records.

While the boat continued to get faster, a more fundamental design issue became apparent. With the pilot’s seat in the rear of the main hull, trying to keep the boat pointed in the right direction was a challenge. It was, Larsen describes, “like trying to fly an arrow backwards. It would try to turn around and fly the proper way with the weight at the front and the feathers at the back, by turning laterally into the wind, or vertically if it had to.”

On one memorable occasion, Vestas SailRocket took off and performed a complete backflip, leaving Larsen upside down in the water and the boat once again in pieces. The video of this crash went viral on YouTube and has been played more than 400,000 times. But this was one of many incidents: “We had rounded up into the wind, smashed the wing, and folded up the beam at least four times before we even got to the flip,” he recalls. “Each one of those was a big crash, big repair, damaged wing, broken struts; once we got the boat going really quick, then she started to somersault.”

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Amid all of this, the world record was being pushed further down the track by the kiteboarders with Douglas stealing it from the windsurfers and then Frenchman Sebastien Cattelan being the first sailor to break the 50-knot barrier. But Vestas SailRocket also made its mark. The same day as the backflip, SailRocket became the world’s fastest boat, as opposed to board, at a speed of 47.3 knots.

The following season Larsen and company realized time was running out for Vestas SailRocket. They had an unofficial run of 49.38 knots and a peak speed of 52.78 knots, but the runs were still very much do or die. Larsen endured another full backflip and a separate catastrophe when the forward beamstay broke, causing the beam to fly back into the main hull and the boat to fold up, putting the pilot in the hospital. “It went from over 47 knots to a standstill, and the beam came back at me like a cricket bat,” says Larsen. “I still rate that as the most violent crash in yachting yet.”

With Vestas SailRocket reaching the limit of its potential, the team was already deep into the design of Vestas SailRocket 2, harnessing all the knowledge they’d learned from the first boat.

While Barnsley spearheaded the design of the first boat, the principle designer of the second was Chris Hornzee-Jones, a structural engineer and aerodynamicist, who heads the company AeroTrope and designed the wingsail for the first Vestas SailRocket.

Launched in March 2011, Vestas SailRocket 2 incorporated all the fundamental features of the first boat: a hull to windward incorporating the all-important foil, a single crossbeam, and a wingsail inclined to weather by 30 degrees. In other ways, however, it was a significant step forward. At 40 feet long by 40 feet wide, it was slightly bigger, and the hull was now more like a glider fuselage sitting on two short floats at the bow and stern, with the rudder mounted on the forward one. To leeward the wingmast sat atop a third float.

Most noticeable was that while the floats pointed in its direction of travel, the fuselage was offset to starboard by 20 degrees to point into the direction of the apparent wind in order to minimize drag at high speed. They also “reversed the arrow,” putting the cockpit in the bow of the fuselage. They enlarged the wing from 172 sq. ft. to 193 sq. ft., added a hooked section at the bottom of the wing (giving it a hockey stick profile), which acts as an endplate for the wing and also provides some control over how high the leeward float flys.

In the cockpit, in addition to the steering wheel, the controls Larsen uses during a run are the mainsheet and the control for the flap on the outboard extension of the wing. There are also controls for raising and lowering the main foil and the low-speed skeg, and controlling the wing when stationary.

During the 2011 season, the team made solid progress. Vestas SailRocket 2 proved more controllable and stable than the previous boat, and in two seasons of use it experienced none of the same catastrophes that afflicted the first boat. However, regardless of the wind speed, the new boat couldn’t surpass the low 50-knot range. By this stage, Douglas had pushed the record to 55.65 knots.

The culprit proved to be the foil, mounted on a bracket well aft on the windward side of the fuselage.

In 2011, the team trialed two foils. Both were L-shaped, one a conventional asymmetric teardrop shape—with a similar section to an IMOCA 60/Volvo 70 daggerboard—the other a ventilating foil. With the former both the low- and high-pressure sides of the foil are put to use, but when traveling at speeds approaching 60 knots the foil cavitated. This is a common problem for propellers, caused when pressure on the low-pressure side of the foil becomes so low it causes the water to vaporize, effectively detaching it from the foil. With only one side of the foil working, the performance of the foil drops suddenly, with potentially disastrous effects.

A ventilating foil with more of bullet shape (a sharp leading edge, and a blunt trailing edge) is, in hydrodynamic terms, much less efficient: Its effective working area is much reduced, and it creates more drag. However, this shape theoretically removes the cavitation issue and allows the foil to operate smoothly at speeds well in excess of those where a conventional foil starts to struggle. During the 2011 season Vestas SailRocket was mostly being sailed with this foil, only it failed to ventilate properly. In desperation the team took out the grinder and progressively shortened the foil in 6″ chunks, down from 3’3″ to 1’9″, before returning to base to consider the data.

Back in Great Britain, the team planned to build a new foil, but was unsure what exactly to build. Talking to the experts only caused more confusion. They were advised a ventilating foil shouldn’t be able to get beyond 30 knots, but they had achieved speeds in excess of 50 knots with it. So they reverted to their original concept of a ventilated foil, only a depth of around 2′ submerged and a chord of 10″ at its maximum—about 60 percent of its original area. They also fitted Cosworth data loggers to the foil to establish where cavitation or ventilation was occurring.

The eureka moment came not with the new foil on its own, but when they added a strategically placed fence to prevent ventilation in an area of the foil that shouldn’t have been ventilated. And the rest, as they say, is history. Initially they set a new record of 59.23 knots, and 10 days later Larsen managed 65.45 knots with a peak speed of 67.74 knots.

What’s it like at 60 knots? “It depends on how close I get into the beach,” says Larsen. “If I stay out of the rough stuff, it is a short, sharp, bumpy ride, like on a high speed powerboat. This thing doesn’t knife through the waves, it skips over the top of the small chop. At the back of the boat it is pretty good, just riding on a foil, it is pretty civilized. The visibility is brilliant. I have got no sunglasses or visor on. There is no spray coming into the cockpit, compared to the last boat. I only feel a little bit of spray just when I start up.”

At present there are no plans to progress with Vestas SailRocket. The point has been proven. From the heavens Bernard Smith, who passed away on Feb. 10, 2010, can smile. Larsen is adamant the concept will go faster; in theory there is nothing to stop this genre of boat from hitting 100 knots. But it will require another foil. With his offshore background Larsen is intrigued to see if the neutral stability concept can be developed for more practical applications, but only if it makes boats like the 131-foot Banque Populaire maxi tri [the outright ’round the world record holder at 45 days] look like pedestrian dinosaurs.

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