Naish Foils - Shimming the Stabiliser

Emmett said..




Initial cut parallel to the fuselage. The put a nice looking radius curve on the front corners, and round the rear corners for some safety. Then you should taper the cut material when looking from the front-on view. Round the tapers to fair into the foil top and bottom and ensure the leading edge of the tips are thin and fair. If you don't know what the shape should look like then it might help to aim fast running hose water at the tips and observe the ease of water flow.

On my HA280 I cut the winglets off completely and gained some speed, but you also lose a lot of yaw stability. Being yaw loose is good for flat turning at low speeds, but lots of yaw stability is best for high speed. eg. Look at all the fast kitefoil stabilisers. So you are probably better off starting with the HA220 and cutting only half of the winglets off, to retain some up-turn in the tips, to retain some yaw stability.

When you lose yaw stability you also increase the risk of a mast ventilation. Which is mostly a problem going upwind at speed in chop with the C100 mast. But without winglets, I could also ventilate the mast going downwind with foil flat and near the surface. The mast just lets go the leeward side and you get an odd feeling until it re-grabs.

To go faster, try using the stab position one fwd of full aft. I found the most rear mounted position was slower. Although more pitch stable and more pitch control, I presume it generated more drag.

Also to go faster, you can consider sanding your rear foils to be thinner. It makes a big difference. But it's easy to ruin the shape so be cautious if you don't trust your eye or sanding fairing skills. I did my best speeds with a HA280 that was substantially cut down on the tips and also about 0.5mm thinner. Really good pitch control so I could bring the 914 close to the surface.

If you have the 914 front foil, you can cut (sand) just 10mm off each tip to remove some of the negative twist, and it'll go a little faster too, at the cost of a little lift at take-off speeds.