Vestas Sailrocket straight into it - Over 50 knots on second run!
by Paul Larsen 17 Oct 2012 12:03 BST
16 October 2012
It was a perfect day over on speed-spot today. The wind was 21-25 knots, the sun was shining and the tide was high. All the little sand-piper birds were sheltering behind the little sand-dune tussocks. They were bunched up there in little 'crowds' and after watching the recent Olympic sailing from 'The Nothe' bank in Weymouth, I kidded myself that they were standing on the grand-stand waiting to watch VSR2 do her thing. Let's face it, this is as close as you'll get to a crowd out here! We went straight into getting set up for a run and in general everything went smoothly. The day looked great and I was reading gusts of 23 knots on the Tacktick display and Helena was seeing peaks of 25 knots further down the course. I was confident we were going to see a fast run... or at least get good info.
The start up went pretty smoothly and sure enough, VSR2 broke free of all the low speed drag and got up on the plane. Ah, sweet release! I held a course into the beach to get into the flat water and then bore away down that magical mile. Everything felt fine. The steering was light and responsive and the acceleration came in bursts. We were easily well over 40 knots in a matter of seconds. Some times she would feel slippery and other times it felt like she was being dragged back... or was pulling drag. VSR2 seemed to break free again about 100m after the timing hut and surged up to a steady peak speed just before I turned away from the beach to give myself room to do a big round-up into the wind to stop completely. It was a solid run that ticked a lot of boxes. I was happy to see 50.11 knots on the small GPS to confirm what I would have guessed. The average was 45.57 knots over 500 metres.
I can't get too excited about low 50's anymore. we have hit that speed many times with both boats and every foil we have ever used. The concept on which the Sailrockets are based has the power to pull any half decent foil up to this speed. We are openly targeting 60 knots now. I have been stuck under the low 50 knot glass-ceiling too many times and this boat/foil configuration is all about breaking through it. No complaints yet mind you. We did just hit 50 knots with our second run with a whole new foil. That run proved the following points...
- the smaller foils can get started in modest conditions
- the new foils don't seem to have any huge drag penalties and they must be well ventilated down their blunt bases just to achieve 50 knots. This already gives validation for the foil design path we have chosen
- the new rudder gives great control and seems very responsive
Now that we have the new SMD pressure sensor package on the foil which is being logged by the COSWORTH data logger, we don't have to do a bunch of runs to get the info that we want. We used to do runs to try and get the feel or do a process of elimination in order to go faster. Now we can simply look at the data and see solid information. You don't have to guess what is down those dark alleys anymore as you can turn the lights on. Doing 50 knots on our second run has put us a bit further forward than I was expecting. I decided to leave the perfect conditions on speed-spot and return to the Operations base at the Walvis Bay Yacht Club to digest the data we had just obtained. Already I have seen the following...
- We had relatively high pressures down the base of the foil i.e. we weren't being sucked back by low pressure 'cavities'.
- the rear pod was sitting very low. This means we weren't riding as high as we should be on the foil.
So now we have to start the real fine tuning of the beast. To do this we have to mount the new strain gauges on the rudder shaft. These tell us how much load is on the rudder at high speed and therefore how well balanced the boat is. From this we determine if we need to swing the beam and wing forward or aft. I wanted to see if the new small rudder did the basics before I wasted a £300 strain gauge on it. Ben has already removed the rudder stock from the boat and it sits in front of me now. We will be up first thing in the morning rigging VSR2 up on the lawn. We have to make the most of the still morning to do all the little jobs in preparation for another days sailing.
I'll leave it at that for now. We had a very good day as we jumped up the speed ladder in one bound with the new foil... but to have a great day... we need to see that 60! The greed for speed eh?
Cheers, Paul
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