ALONG a stretch of Namibia’s wind-blasted Atlantic coastline, one man is about to try to sail faster than any sailor has ever done before. This attempt to set a world record requires technical expertise, courage and luck. It will take place in the Vestas Sailrocket 2, which barely even looks like a boat and is, astonishingly, based on a design that is 40 years old.
For the past few months, the team has been making trial runs. If their innovative design hits 60 knots (111 kilometres per hour), it will change the future of speed sailing.
Advertisement
“Going from 50 to 60 knots is like breaking the sound barrier,” says the boat’s pilot Paul Larsen.
But it won’t be easy. In 2008, the first version of the boat flipped out of the water in just as it was approaching record-breaking speeds.
Although based on the Isle of Wight, UK, the team chose Walvis bay in Namibia for its strong and predictable daily winds – which frequently hit 20 knots as they blow in from the Atlantic. The existing speed sailing record of 55.65 knots was also set there, by . To beat Douglas’s record, the VestasSR2 must reach a higher average speed, in one direction, over a distance of 500 metres. This will mean hitting peak speeds of more than 60 knots.
Although VestasSR2 is officially classed as a sailing boat, there is not a billowing sail in sight. It is made almost entirely of carbon fibre and looks like a glider’s fuselage supported by two floats. A third float hangs under a beam, positioned towards the back of the boat at a 90 degree angle. Above this outer float sits a sail, known as a wing, made from carbon fibre ribs and covered in polyester film. The sail produces huge amounts of forward thrust – enough to allow it to travel faster than the wind itself – but just like any sail it can also tip the boat over.
“The boat has a carbon fibre wing instead of a billowing sail and looks like a glider on floats”
A way to counteract this is to use a hydrofoil beneath the boat. Placing a mirror image hydrofoil underneath the boat produces an equivalent torque in the opposite direction from the sail. Because it is balanced, the boat itself can be very small and light – just 275 kilograms. As long as the hydrofoil keeps working, the boat’s speed is only limited by the available wind; eventually the wind tips traditional yachts over.
The hydrofoil can be 800 times smaller than the wing and still keep the boat in balance because it is racing through water, not air, which is denser and thus creates more torque.
The idea of adding a hydrofoil to a sailing boat was first conceived by Bernard Smith, a rocket scientist, who wrote about it in his book – The 40 Knot Sailboat – in 1963 (see, “Messing about with boats”). Sailrocket’s founder Malcolm Barnsley, an engineer from wind turbine firm Vestas, stumbled across the book during his quest to design the world’s fastest sailing boat. Barnsley realised the hydrofoil could allow him to push speed sailing to an entirely new level.
“Once you demonstrate that this principle works then you have shone the light on the path,” says Larsen. “Like the sound barrier, there is no second sound barrier. Going faster is just back to balancing the same principles of power and efficiency.”
For VestasSR2 to reach 60 knots it needs a large sail to extract enough power from the wind. This requires an equivalent force from the hydrofoil in the water to keep the boat balanced. But at around 50 knots, the pressure behind the hydrofoil gets so low that the seawater starts to boil at ambient temperature and spontaneously forms bubbles of gaseous water. This is known as cavitation and destroys the effectiveness of the hydrofoil and the balance of the craft. The bubbles make the flow unstable and cancel out the torque produced by the hydrofoil. And without the torque the boat loses balance.
However, VestasSR2 is now equipped with a supercavitating hydrofoil: a wedge-shaped fin that is designed to create one big bubble that covers the whole upper surface. This design has been tried on some boats in the past without success.
Why should this time be different? After a slow start in putting the design to use, the team is now making regular runs at beyond 50 knots. This week it is inviting officials to register their attempt at breaking the world record. All they need now is wind.
, holder of the wind-powered land speed record, says the challenges in sailing at such high speeds are huge. “Breaking a wind-powered speed record is roughly a 50 per cent split between technical credibility and luck with weather conditions. The biggest challenge is to be technically perfect at precisely the right time to take advantage of a freak set of conditions.”
Surprisingly, Larsen says he clocked 54 knots, the fastest so far, when he took a passenger on board. “He had the ride of his life. This boat will do the business. It will beat the current world record. I know that now. The question is how much we can get out of it.”
Messing about with boats
Bernard Smith, a rocket scientist working for the US navy, began designing a high-speed sailing boat in 1957 when he was posted to a naval testing facility in China Lake, California. He wanted to see how fast he could make a model sailboat go on the shallow, seasonal salt lake.
He found that the main problem with pushing sailing boats faster was the side force on the sail that tries to tip the boat over. Crews piloting fast yachts manipulate the weight distribution of these boats by leaning out from the hull on the windward side to try and extract as much power from the wind as possible.
Smith repositioned the sail so that it could be balanced by a hydrofoil, a wing running in the water beneath the boat. In principle, this can create a vessel where all the wind force is converted into thrust leaving no net torque on the hull.
Following his initial work, Smith published his book The 40 Knot Sailboat in 1963 and continued working on small boats and models.
It wasn’t until 2007, at the age of 98, that he learned VestasSR1 had reached 40 knots, the first boat based on his concepts to do so. Later in the same year, the boat hit 50 knots. He died in 2010.
