2013. Sixty-five knots under sail, how is that possible?

Welcome to the special section “GdV 5th Years.” We are introducing you, day by day, An article from the archives of the Journal of Sailing, starting in 1975. A word of advice, get in the habit of starting your day with the most exciting sailing stories-it will be like being on a boat even if you are ashore.

Sixty-five knots under sail, how is that possible?

Excerpted from the 2013 Journal of Sailing, Year 39, No. 03, April, pp. 86-93.

The fastest sailboat in the world is not the AC 75 of the America’s Cup but a strange 12-meter object with only 22 square meters of sail that reached 65 knots of speed in 2012. Everything you need to know about the world’s craziest record.

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The impossible has become possible: the sailboat has become faster than the motor boat. At the end of a project developed over ten years, Australian Paul Larsen flew over the Namibian sea at the insane speed of 65.45 knots (121 km/h).

Let’s stop for a moment and think carefully: 65 knots. Let’s close our eyes and slowly repeat it over and over in our heads: 65 knots of speed with a sailboat. At a time when everyone is shooting their mouths off, telling with disarming simplicity that they have sailed in 40 knots of wind, as if 20 were little, and that they have faced 10-meter waves, because it seems that 5-meter ones no longer make an impression, the news of 65 knots of speed (65.45 to be precise) is in danger of going unnoticed. Which would be criminal, since this “is not science fiction, but science.” Yes, a sailboat, Vestas Sailrocket 2 by Australian Paul Larsen, has managed to go 121 kilometers per hour, catapulting the history of sailing into a new, hitherto unknown era. It matters little that this is a record, indeed better not to talk about it at all, because one would risk losing sight of the sensational fact. Sixty-five knots is a figure so “beyond” any speed previously achieved by any sailing vessel (boat, windsurfer or kitesurfer that is) that it deserves much more attention than a simple entry in the speed record book.

An ‘idea born while sailing on multihulls.

The leap forward made by Paul Larsen is historic. The chronology of man’s challenge in pursuit of maximum speed under sail tells that it took thirteen years to go from 30 to 40 knots and that it took as many as twenty to break the 50-knot wall. Then, in just five years, it went directly to 65 knots, without even going through 60. It all happened in Namibia, in Walvis Bay, on a magical November in 2012 (a few months ago) when Paul Larsen flew over the water (which is always flat there, even when the wind is blowing hard) with his Vestas Sailrocket 2, finally seeing a decade-long dream come true. That’s right, because the Australian sailor, a longtime resident of England, had gotten the idea of becoming the fastest man in the world on a sailboat earlier this millennium, when he had been part of several crews in transoceanic and around-the-world races on maxi multihulls. While his teammates were simply striving to make the boat go as fast as possible, he also wondered how a 30-meter trimaran could go so fast and began to fantasize about new solutions and impossible speeds. When we write that Paul Larsen flew over the water, we mean that he sped over the surface of the sea and forget that, instead, he also flew in the true sense of the word. It happened with his first prototype Sailrocket(which translated really means “sail rocket“), on which the cockpit was positioned at the extreme stern. As the boat picked up speed, the bow began to rise, gaining lift, and, several times, Larsen found himself somersaulting backwards into the sky and landing ruinously on the water . “Once” – recounts his companion, Helena Darvelid – “he is He came out of the emergency room with his head so swollen that he could no longer get his helmet on. Which was good, because otherwise he would have immediately attempted another run “. When talking about “racing,” it should be remembered that the absolute sailing speed record is calculated on the average speed recorded on a measured base of 500 meters. In fact, with Vestas Sailrocket 2, Paul Larsen even touched a top speed of 68 knots (126 kilometers per hour).

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It works like a giant windsurfer

Its second “sail rocket” was launched in 2011 and is an evolution of the first Sailrocket, built in 2004 and modified several times (it even had a fabric sail at first). In addition to being significantly larger, with a length and width of 12.20 meters compared to 9 meters for the first prototype and with a wing area increased from 16 square meters to 22 square meters, the biggest difference lies in the pilot’s cockpit positioned forward to keep the bow in contact with the water at all times. Of course, talking about length and width for a sailboat like Vestas Sailrocket 2 is quite relative. These measurements, in fact, refer to the main elements that constitute it: namely, a fuselage that resembles that of a glider in shape, from which starts a crossbar of the same length, but with an airfoil section, at the end of which the rigid wing is positioned. Now, it must be imagined that this “L” structure does not sail straight, but rotated at an angle of 20° to the direction of the course. To understand, when Larsen looks forward, his eyes are not directed toward the bow of his fuselage, which, instead, is aligned exactly against where the apparent wind is coming from, to offer as little drag as possible. Vestas Sailrocket 2 is in fact a tripod that rests on three skids each with a volume of 300 liters and functions as a giant windsurfer.

To pick up speed, he starts at slack and, as he accelerates, positions the fuselage to be sideways from the true wind direction, which coincides with the 20° apparent wind. Oriented at this angle to the longitudinal element, thus in the direction of heading, are also two of the three skids, while the one at the bow, to which the rudder blade is attached, is controlled by Larsen to direct his “rocket.”. Just like a windsurfer, at the beginning of the acceleration Vestas Sailrocket 2 is difficult to control. For this, there is a fixed fin on the stern skid that is raised once the boat stabilizes. At maximum speed, however, the left skid, located at the foot of the wing, rises completely out of the water to decrease friction. This is achieved by the airfoil of the transom and the horizontal extension of the wing itself, which generate the lift necessary to make Vestas Sailrocket 2 sail as “light” as possible, just above the surface of the water. The sail (which has an asymmetrical profile-so the boat can only ever sail in one direction and at the end of each run must be towed back to the starting point with the wing down), again as on windsurfs, is angled to create that perfect balance between vertical lift and lateral force that generates the most efficient forward thrust. Influencing the operation of this perfect aero and hydrodynamic system is the foil, which has a drift plane angled at the same angle as the sail to work in tandem on lift and thrust. To combat the phenomenon of cavitation, its profile is also asymmetrical and its section is wedge-shaped: pointed at the leading edge and truncated at the trailing edge.

Andrea Falcon

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