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Vestas Sailrocket 2 - the search for a breakthrough

by Paul Larsen on 13 Sep 2012 13 September 2012
Vestas Sailrocket in action © Helena Darvelid / Vestas Sailrocket

The VESTAS Sailrocket 2 project will be returning to the waters of Walvis Bay, Namibia this September with a new hydrofoil package which they hope will bring them an outright world speed sailing record.

The record currently stands at 55.65 knots (64 mph) and is held by American Kite Surfer Rob Douglas. VESTAS Sailrocket 2 was built in the VESTAS R+D facilities on the Isle of Wight and launched in the Medina River in March 2011. The project then relocated to Namibia where ideal conditions occur on a regular basis.

From its launch in the UK, VESTAS Sailrocket 2 rapidly progressed up the speed sailing ladder and after only 23 runs, hit speeds over 50 knots down the magical mile long course at Walvis Bay's 'Speed-spot'. The team then made continual improvements to the boat and tried a number of underwater foil configurations but seemed to be hitting a 'glass ceiling' in performance in the low 50 knot speed range regardless of which foil options they tried or how much wind they sailed in.

The Cavitation Barrier

Chris Hornzee-Jones - AEROTROPE/VSR2 designer: "Once you start going through the water over 50 knots you are going to start encountering a phenomenon called cavitation. This can be likened to the hydrodynamic equivalent of the 'Sound Barrier'. The property of the water changes as it turns from liquid to vapour on certain parts of the foil. This requires a very different approach to how you design them. The problem gets even more complicated as air from the surface also tries to get sucked down onto the foil and cause it to lose grip. This mixture of air, vapour and very high-speed water is all very dynamic and extremely hard to model by computer or even in high-speed flow tanks. Most projects to date have simply pushed conventional foil theory to the limits and that's why speed sailing is stuck at the current speeds in the low 50's. VESTAS Sailrocket 2 was designed from the outset to be a breakthrough boat. It is designed to be an ideal testing platform for trialling new foil concepts which will allow us to break through this 'glass ceiling' and perform at speeds well over 60 knots."

Paul Larsen - Australian project manager/pilot of VSR2: "This is the second craft we have developed for this record. We saw the potential of the concept revealed with our first boat but this version is aiming to use that potential to knock down some of sailings biggest physical barriers. If we can do that then the world records will come with the territory. From my perspective in the cockpit, this version of the boat is a delight to sail. It is much less traumatic than the first boat. VSR2 is just ambling down the course at 50 knots in a very stable manner. Hopefully these new foils we have designed will allow her to really show her potential. I'm sure she won't feel so docile over 60 knots. I think she's patiently waiting for us to gain the understanding to release her from all the drag and give her free rein."

VESTAS Sailrocket 2 is indeed a radical craft. It looks perhaps more like a plane than a boat because a lot of attention has been focused on the aerodynamic efficiency and stability of the craft however, she still relies very much on the hydrodynamics to allow her to carve across the wind. It is based on a concept where all the overturning forces typically associated with sailing craft are removed. This allows the boat to use the wind created by its own speed to generate a lot of its ultimate power without actually getting overpowered. Whilst VSR2 might actually be sailing in only 25 knots of real wind, at full speed the lightweight, carbon fibre boat and its rigid wing sail feels like it is sailing in over 60 knots of wind and yet doesn't require traditional systems of weights and levers to remain stable.

Malcolm Barnsley - VESTAS test engineer/VSR2 design team: "We are delighted with the way the boat has developed to date. It has been pushed very hard by the sailing team and has shown time and again that it is a great platform for taking new foil designs to their limit in the 'real' world. We have learnt an immense amount already with this boat. Even though our first version of very high speed foils was shown not to be the answer, they also showed us certain aspects that were right. With the new foils we have incorporated these aspects and hopefully used our understanding to design out the parts that were holding us back. We are heading into new territory here. It's a dark alley and of course it is hard to be certain of what lies ahead until you illuminate it with your own knowledge. We have followed a path that seems logical and have chosen what we also hope is the safer, reliable option rather than the extreme one. The potential of this boat is enormous but if these foils allow us just to reveal a portion of that potential... then world records should fall."

The new foil is currently being manufactured in Bristol. Team members will shortly head down to Namibia where VESTAS Sailrocket 2 is currently located. They will assemble the boat and base in preparation for the arrival of the rest of the team and the new foil. The focus will be on developing the new foil and some of its 'add-ons' to see if it truly is the missing piece of the puzzle that will allow the team to realise their dream. The team is still looking for answers and they know that nothing is certain until proven beyond doubt in the real world. If the new foils do what they are supposed to do, a World record attempt will be booked with the WSSRC (governing body) in the October-December period this year.

Updates will be posted regularly on www.sailrocket.com

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