Radical SailRocket yacht targets world speed record

  • Photographs by Helena Darvelid/Vestas SailRocket
  • Pilot and project leader Paul Larsen (second left) with his support team. Photographs by Helena Darvelid/Vestas SailRocket
  • The Vestas SailRocket 2 team attack the foil with a hacksaw, hoping that by reducing its length, it would work as planned. Photographs by Helena Darvelid/Vestas SailRocket
  • The area off Walvis Bay where the team performed their speed runs. Photographs by Helena Darvelid/Vestas SailRocket
  • Since the craft has to sail in only one direction to make its record runs, its asymmetrical wing is rigged for a starboard (right) tack to suit the Walvis Bay location. Photographs by Helena Darvelid/Vestas SailRocket
  • The outlandish-looking Vestas SailRocket 2 was designed for one purpose, and one purpose only – to be the fastest sailboat on the planet. Photographs by Helena Darvelid/Vestas SailRocket
  • The outlandish-looking Vestas SailRocket 2 was designed for one purpose, and one purpose only – to be the fastest sailboat on the planet. Photographs by Helena Darvelid/Vestas SailRocket
Date:1 February 2012 Tags:, ,

In pursuit of the outright world speed sailing record. No one said it would be easy…

If you’re intent on breaking the outright world speed sailing record, you’ll need a radical design ““ perhaps something on the lines of the Vestas SailRocket 2. But even then, as pilot and project leader Paul Larsen and his team soon discovered, breaking through the elusive 60-knot (111 km/h) barrier is far from plain sailing.

On the world stage, Namibia’s small coastal town of Walvis Bay borders on the insignificant ““ unless you’re a sailing fanatic who’s addicted to speed, that is. Thanks to the predominant south-easterly winds that blow off the Namibian coastline between the months of September and December each summer, it’s the ideal spot for sailors from around the globe looking for a stab at becoming the fastest man (or woman) under sail.

It comes as no surprise to learn that Larsen and his team are intimately acquainted with this part of the world. They last visited Walvis Bay in 2008 with their first design, the Vestas SailRocket (VSR) 1, which still holds the B class (up to 21,84 m² of sail) world speed sailing record of 87,72 km/h. Unfortunately, although they managed to hit peak speeds of 96 km/h on a number of occasions, the outright record remained frustratingly out of reach. (On their last run, just as things were looking promising, the boat became airborne, then flipped.) Dejected, everyone headed back to the drawing board, and so was born the VSR 2.

This time around, the design team opted for a different approach. Rather than chase the record with just another version of the VSR 1 hull, they wanted to create a radical “breakthrough” boat. Their aim: to overcome the inherent limiting factors that prevented sailboats from attaining the kind of speeds that enter the record books.

Malcolm Barnsley, Vestas senior test engineer and leader of the VSR 2 design team, explains their thinking: “What we are attempting to do can be likened to that period in aviation when the focus shifted to breaking the sound barrier rather than the speed records that preceded it. If we’re successful, the outright record will not only come with the territory, but the equation for achieving 100 knots (185 km/h) or better will have been written and validated for the next generation. We do not expect this challenge to be easy, or the results to come automatically. The unexpected comes with the territory.”

Living with cavitation
Topping the Barnsley’s team’s to-do list was the need to tackle the problem of cavitation head-on; they had to fi nd a way to exploit this speed-limiting phenomenon to their advantage. Cavitation happens wherever fluids are subjected to very low pressures (think boat propellers, hydraulic pumps and even the fins of fast-moving fish such as tuna). Because sailboats rely on fins or foils to counteract the side-force of the wind and avoid slipping sideways, when they reach speeds of around 110 km/h, cavitation raises its ugly head and effectively pulls up the handbrake.

Here’s what happens: conventional foils rely on the water passing over both of their sides, much like air over the wings of an aircraft. On one side, you get high pressure that creates lift; on the other, the low pressure actually sucks the wing upwards (or the foil sideways).

Under water, it’s typically when this suction becomes too great that water turns to vapour, and cavitation occurs. The foil then loses grip on the water and the pressure side of the foil now has to do all the work; this makes it skid sideways and creates drag.

Larsen elaborates: “Imagine going for a speed record in your car, and right when you’re approaching maximum speed, you open all the doors wide and pop the bonnet! Not only do you now need double the power to go any faster, but you also risk a major loss of control.”

To get around this, the design team “threw out” the traditional teardrop foil profile, and instead went for a ventilated design where one side of the foil always travels in the low-pressure vapour bubble. Says Barnsley: “The profiles we chose are more like sharp wedges, where only one surface at a greater angle is utilised. There are many high-speed power boats that use propellers with this profile, but until now it has never been done effectively on a sailing boat.”

On the level
The design team’s next major consideration was stability. “The first version was a great boat, but a lousy aeroplane,” quips Larsen. “This time around, we wanted the VSR 2 to be stable in both environments.”

This was achieved by positioning the boat’s wing at an “inward” angle of 30 degrees to match the inclination of the ventilated foil on the opposite side of the hull. The end result is that the opposing forces of wind and water are in alignment, creating a unique stabilising effect. “It’s like someone trying to shove you over by pushing at the soles of your feet. They could push you sideways, but not over. This allows us to handle a lot more power without tipping over, like 99 per cent of other sailing craft. As a result, the only significant response to wind gusts is a change in speed.”

To reduce drag and increase stability even further, both the main fuselage and beam were angled at 20 degrees to the actual point of travel. This was done to make the boat point directly into the direction of the apparent wind (or the combination of two winds – the one generated by the forward motion of the boat and the true wind itself) when travelling at high speed. Since the VSR 2 has to sail in only one direction to make its record runs, its asymmetrical wing is rigged for a starboard (right) tack to suit the Walvis Bay location.

Foiled by the foil
Larsen and his team launched their official record attempt on 18 November last year (they were allowed a 28-day window). Monitoring proceedings was Mike Ellison from the World Speed Sailing Record Council (WSSRC), the sport’s governing body. Their goal: to try and break the current record of 103 km/h set by American kite surfer Rob Douglas in Luderitz, Namibia, in October 2010. To better it, the Vestas SailRocket 2 would have to hit peak speeds in the region of 111 km/h.

Sadly, it didn’t happen. Try as they might, they couldn’t break through the 96 km/h barrier. In their attempts to find a solution, they experimented with different hull configurations, such as raking the beam and asymmetrical wing forward, to no avail. They made changes in the foil configuration, hoping that by angling its nose upwards as much as possible, they would be able to force its upper, more horizontal section to generate more lift and better ventilatation. That didn’t work, either.

Eventually, after running out of options, they had to face the unpalatable truth – the ventilating/wedge foil simply wasn’t working the way everyone had hoped it would.

But these guys weren’t quitters. In a lastditch bid to salvage their record attempt, the team resorted to attacking the foil with a hacksaw, eventually removing 45 cm from its tip in the hope that this would make it lose its grip and become ventilated – but again, nothing happened.

When it comes to radical design concepts, what seems to make perfect sense in the lab doesn’t always work when put to the test in the real world. That’s exactly what  happened here. Although the foil was designed to be ventilated, this never happened. Observed Larsen as their 28-day window of opportunity drew to a close: “It has shown itself to be relatively fast…but it won’t get any records.”

Finally, to add insult to injury, adverse weather over their remaining three days scuppered any chance of a last-ditch record attempt before the team’s return to the UK. That’s sailing for you.

To find out more about the Vestas SailRocket 2, and to read Larsen’s comprehensive blog, visit http://sailrocket.com

The outright world speed sailing record
The outright world speed sailing record is determined by taking the average speed of a craft between two points set 500 metres apart. All records are observed and ratified by the sport’s governing body, the World Speed Sailing Record Council (WSSRC), and the title is open to all waterborne sailing craft, from kite surfers to maxi multihulls. The current record of 55,65 knots (103 km/h) was set by American kite surfer Rob Douglas in Luderitz in October 2010.

Related content –
Video: Watch SailRocket’s fastest trial run in October 2011 in Namibia, peaking at over 100km/h

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