The new UK-built speed hunter Vestas Sailrocket 2 is an electrifying bit of kit
It was a beautiful, cloudless and calm day in Cowes yesterday for the launch of Vestas Sailrocket 2 – and just as well. This was the first time this delicate, almost sculptural speed sailing machine had been placed oh, so gingerly in the water.
Even so, watching it craned in, millimetre by millimetre, was nerve-wracking.
The strange machine looks like a huge advance on Paul Larsen’s and designer Malcolm Barnsley’s first Sailrocket, which was launched in 2003. It has an appearance that’s part supersonic fighter, part sailing foiler, and stationed beside this sleek jet the original, groundbreaking Sailrocket seemed like the Wright brothers’ biplane.
When Paul and Malcolm set off chasing the ultimate speed sailing record back then they were trying to beat 46.5 knots. But the record has been raised and raised and only briefly was Sailrocket 1 the fastest boat ever made.
“Until the point that the boat was parked in 2009 the record went up by 20%, or 9 knots,” says Paul Larsen. “It was like a mirage. As soon as we got near the record had moved on.”
Today, it stands at 55.6 knots and is held by a kitesurfer.
Paul Larsen and Malcolm Barnsley think it can go higher and that the equation will – must – swing to a foiling yacht to go through the 60-knot barrier.
So this is the theory and the aspiration behind the electrifyingly new Vestas Sailrocket. It’s an astonishing piece of kit, most beautifully made of carbon fibre. It has a satisfying simplicity of form yet is of fiendishly brain-warping complexity.
It would not look out of place in a sculpture park. But will it work?
“We are competing against kitesurfers, the simplest craft imaginable. So we looked at the real problems of speed sailing and the hurdles that prevented a quantum leap.
“But to solve problems we’ve added complexity and we will have to go through everything carefully to test them. We haven’t proven they will work yet,” says Paul Larsen candidly.
So how exactly does Vestas Sailrocket 2 function?
Well, er, frankly I’m probably not the best person to ask – try any of the aeronautical or mechanical engineers milling intensely around this beauty – but like original Sailrocket the driving wing section of the new boat and pod beneath become airborne and the orange hull lifts on a bow foil and the L-shaped foil further aft to fly through the water at high speed.
One of the keys to speed is all in the design of the foils. A big barrier to high speed has proven to be cavitation. Let me attempt this one…
Any lifting surface that operates at high speed in the water will eventually experience some form of cavitation as the speed increases. Put simply, cavitation occurs when the water flow on the low pressure side of the foil gets so low that it ceases over the foil surface and a vacuum or cavity appears.
Once this happens a foil can no longer produce lift as the density of the medium around it has suddenly reduced.
Hydrofoil section shapes can be designed to cavitate higher up the speed range, but rudders are particularly prone to cavitating as the angle of attack of the foil is being altered through the very act of steering the boat.
It’s these laws of nature that Larsen and Barnsley have considered in the design of the foils.
But the aerodynamic properties of VS2 have been fundamental, too. Once up to speed the boat will be sailing directly into the apparent wind, so slinky is the name of the game.
“It’s half airplane and half boat,” says Paul. “The upper wind speed [sailed in] will be in the 20-30 knot range but we have to be able to do 50 knots at 20 and 30 knots windspeed.”
Questioned on the forces involved, he explains: “The foil is quite an extreme piece of kit, but it’s designed to go above 60 knots. But how that foil performs is a big unknown.”
But he adds: “The boat has the equivalent drag of a 74cm round ball at 60 knots.”
I don’t pretend to fully understand it, so here I’m going to show some detail photos of the new Vestas Sailrocket with some of the explanations and comments given yesterday.
By the way, this incredible craft won’t be in the UK for long. It goes into a container to be shipped out to Namibia next week. Walvis Bay, Namibia is where almost all the record runs are done because of the frequency of flat water and near-perfect wind conditions.
Paul Larsen introducing the boat. Note the wingsail behind him. The two sections above the strut fully feather by 360° so VS2 can be towed back up the course for another run. The lower section is fixed but can rotate +/-40° for backwinding
The all-up weight of Vestas Sailrocket 2 is a featherweight 274kg.
The flat section at the base of the wing stops pressure loss from wind spilling off the bottom and it also compresses pressure against the water surface to lift the foiling pod, says Larsen.
Another view of where the wing meets the beam, and the axe-shaped pod below. At low speeds, VS2 is steered by moving the beam fore and aft. It swings through 4m. However, at speeds above 25 knots it’s steered with the rudder shown below…
This is the rudder at the front, below the ‘nose cone’. You can see the curved foil below a pod shaped like an axe head. At higher speeds VS2 is controlled with a steering wheel at the helmsman’s seat and the mainsheet
The ‘super cavitational foil’ section
The mechanism that flips the foil up
The crewman’s cockpit with the helmsman’s cockpit just forward
A lot of complex constituent parts, but the whole machine dismantles to fit inside a shipping container.