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A pic you might be interested in. It is a 1=20 scale model of a 90 foot sled scheduled to begin construction in Jan 2003.It will have a canting keel as well as water ballast, and if all goes well,should be rocket fast. This picture was taken last week in the Wolfson Unit for Marine Technology and Industrial Aerodynamics, where the Spitfire fighter was tested. It
is taken at 17' apparent wind angle, with 15 K apparent wind speed. As you might surmise, apparent and true are the same here. We test for the best ratio of Driving force (DF) vs. roll moment (RM). There are sensors at the bow and on the bar thru the hull which measure these forces, which can be seen in the photo. The little D size battery unit just to leeward of the cockpit is a remote video camera with the same view as a sail trimmer! The test goes something like this. The sail trimmer (via remote control) sets the sail trim as he feels best, and a sample is taken via computer. Then he is free to play with trim, aiming for better numbers. When the best numbers are achieved and more samples taken, the sails are trimmed tighter and tighter, until the efficiency is on a deep curve downward. Then the sails are eased back to peak, thru the best numbers, and begin the curve downward, again samples being taken thru the process. This process is repeated for several apparent wind angles, relevant to the sail, and repeated for all the sails being tested. In this three day test, we ran thru 3 jibs, 4 a-sails, and two mains. All in all, we ran something like 250 runs over the 3 days. The goal is to establish VPP's showing the advantages of a Genoa over 100% jib, crossovers from genoa to code "0", "0" to reaching assy. ect. In the end, this will go a long way towards developing the polars for this boat, and will have a definite influence in the finished design of the boat. It is accurate to a point where the large roach main shown held the same slight DF advantage thru the range of angles. Kind of a cool shot that I thought your readers might like. Keith Lorence
We recently featured some shots of a 1:20 scale model of a new 90 foot canting keel sled in the Wolfson Unit for Marine Technology and Industrial Aerodynamics, provided by famous yachtsman Keith Lorence. Some of you have asked to see more pictures, and so here ya go. /ED
The spinnaker pic is at 90' apparent wind angle, and I think it's the runner. We test reachers from 60' to 120', and genoas down to 90'. Runners go up to about 70' and down to 130' which the vpp's show to be the apparent angle while running in 25K. The point of this is to establish crossovers for each sail, as well as refining lead locations and some shape differences. You can see the video camera clearly. But it is not as useful with assy sails as upwind sails. The overhead shot shows the turntable which rotates to adjust the boat's app. angle. We have the sails set up in a full upwind mode, at I believe 17 degrees app.. We tested the differences between a larger 150% sail and the non overlapping sail. To no one's surprise, the bigger sail produced more driving force upwind. Interestingly, the smaller genoa with an outboard lead was better in the 45'-60' wind angles. This is where the little video camera abeam of the cockpit came in handy. It can be zoomed in on the top spreader for a "trimmers" eye view. Very handy. You can see the sail control servos, and the sensor rods thru the hull and on the bow. The viewing window is from the outside, and is empty due to 3 inches of rain falling in two hours, nearly flooding the room.
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