"Computational Fluid Dynamics is just pretty pictures until you prove it by a real world number and everyone was just a theorist on these foils because no one had done it."
came into that orbit, anyone who had an opinion about it - when they saw that number, I think they would have been pretty much as amazed and surprised as we were. Even now we are still up there for sure. We are still pinching ourselves. SRM: The last time we met was in a pub in Weymouth before the Olympics when you were just about to go back down to Namibia with a new foil package to try to break the record. How confident were you back then that the new foils would help you make the breakthrough? Paul Larsen: We had been asking each other 'have we had missed something big here?' We were hitting the same speeds all the time with two different boats and five or six different foil combinations in different wind strengths. We kept hitting that glass ceiling up around 52 knots. We had a Skype call with the design team and told them that this was starting to get pretty weird now. We had tried pretty much everything. We could keep on pouring more power into the equation by going out in more wind but we could see clearly that the acceleration was just going up and flat lining. It wasn't gradually tapering off, it was hitting its limit. So no, until we found the key that unlocked that foil we weren't entirely confident. It was still very much an unknown. We had a theory, but you have got to prove it. CFD [Computational Fluid Dynamics] is just pretty pictures until you prove it by a real world number and everyone was just a theorist on these foils because no one had done it. We weren't copying anyone; it was a different application than you find in high speed powerboats that have tried to foil in the past. SRM: So what was the key that unlocked the potential to those foils? Paul Larsen: We had a bunch of tricks up our sleeve we hadn't tried yet and when we tried the first most basic one - putting a fence on the foil - it was like turning on a light switch. SRM: Explain what a foil fence is? Paul Larsen: It's a little divider on the foil and you basically use it to stop the air from being sucked from the surface down the foil. It stops the foil from ventilating and in our case it stopped it from cavitating too. Previously, having the foil ventilating and therefore not working meant that the other half of the foil was doing all the work and was overloading and eventually cavitating. SRM: How quickly did you realise you were on to something? Paul Larsen: Immediately, even in quite light winds the boat started performing better than it ever had before. The first boat was always better in light winds than the second boat which was a stronger heavier boat. But then all of a sudden the second boat started working and we knew that if we started adding power then that glass ceiling wasn't going to be there anymore. Being honest, unless we could put a camera down there looking at the foil, all that was just another theory. It's pretty hard to put a camera underwater at 55 knots but it would still be fascinating to see what is going on down there though and see how it actually works.
July 2013
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