The innovative, wacky speed machine is launched in Southampton, hopefully a first step towards breaking the 50-knot barrier

Possibly the weirdest and most extreme craft ever to be launched in Southampton took to the water today when Paul Larsen and Helena Darvelid’s Sailrocket was gingerly lowered into the Itchen at Woolston. It has taken 20 months to build this elegant, spidery speed machine, in which Larsen hopes to break the outright speed record under sail and become the first to crack the 50-knot barrier.

The futuristic boat continues to defy categorisation, as Larsen is the first to admit: “It’s not a proa, the Marshall Islanders haven’t done it 200 years ago, it’s not a catamaran or a monohull or a sailboard or a kitesurfer. Everyone tries to put it into a box, but it’s nothing like any of those. It’s a Sailrocket!” he laughs.

Sailrocket was launched from, and built at, NEG Micon, which normally produces huge composite turbine blades for wind generators. The connection is Malcolm Barnsley, NEG Micon’s senior test engineer for wind power, who designed the ingenious Sailrocket and, along with Paul Larsen, proved the concept three years ago using a scale model.

But before any speed records can be set, the Sailrocket team have to negotiate another intensive phase of experimentation, finding out how the behaviour of the real-life Sailrocket differs from that of the model.

“This is exactly a scaled up version of the model in terms of the sail, the weight distribution and everything so it should do exactly what the model did. The model showed that it should do over 50 knots in this configuration, without a wingsail. But now we’ll have ventilation and cavitation issues, so we’ll have to go through the same process as Yellow Pages and all the other [speed record holders].”

Larsen adds that Sailrocket has come out at exactly the weight expected. “Within a kilogram,” he says. “The target weight was 170kg and I think it is probably a kilo or so under.”

The most obvious difference between the model and this Sailrocket is the addition of a wind vane type device on the stern, clearly visible in the photograph above. Paul Larsen explains: “We needed quite a big rudder at the very slow speeds because the centre of effort of the sail is 3m behind the centreboard. It’s only when the apparent [wind] moves forward that you really start to get the boat in balance, and to get over the hump you need a big rudder, which isn’t very efficient at high speeds.

“We looked at changing between rudders and then we just looked at the next step, which was an air rudder. When you’re dealing with 50 knots of apparent breeze blowing at 20° down the boat you can use what is very simple technology on an aircraft. Everything says that it should work and if it doesn’t we just unplug it and go back to a water rudder.”

The first tests of Sailrocket will happen in Weymouth within the next couple of weeks. “We’ll put it up on the beach on a windy day and get used to getting the rig up and down,” says Paul Larsen. “There are a whole lot of systems here which are designed to make the testing period easier, from getting the rig up and down to getting as many runs as you possibly can up and down the course, but when you’ve worked out the configuration of the boat and you’re going for the money run, then you can get rid of a lot of these and start going down to a little bit more volatile technology, like PBO rigging.

“We can take the rudder off and change to a smaller rudder, we can trim the centre of effort of the sail by moving the beam fore and aft. It will allow us to test this concept we’ve got by moving and realigning the forces. For now, we’re not going to commit too much to one thing.”