On 18 Aug 2003 at 20:43, Shawn Baker wrote: > If you have a magnet mounted on the foredeck for a reed switch (say, > N. pole is UP), you could also epoxy another rare earth magnet in a > convenient (and nearby) spot under the deck with the N. pole DOWN), > and the magnetic field will largely be contained between the two > magnets. You could also use a keeper on the magnet, which would do a similar thing. Another thing is to use a mass of iron near the compass to compensate. That's what the two iron balls on the side of a binnacle are for. As well, there are Flinder's Bars mounted on the binnacle. The balls compensate for iron in the ship and the Flinder's bars are to compensate for iron or magnetic fields that are loaded in the ship - the bars can be moved around the binnacle until the compass is corrected. So you can complement your Kevlar and carbon fibre kayak with about 50 lb of iron. :-) Some compasses, like the high-end Ritchies, have more modern compensation mechanisms. I've never fooled with them, but they can be adjusted to compensate for magnetic interference in a boat (like a big iron keel). I haven't seen this feature on the Ritchie kayak compasses, though, only on the bigger ones. Don't know if these work with a rare earth magnet two feet away. Even without a correction device, you can run a line of known azimuth (like a channel line on a navagation chart) and compare the compass reading to the marked reading (including variation or declination) and figure out the compass error. Keep adding (or subtracting) the error when you use the compass. If your compass has a declination adjustment, you can dial out the error with that. You can't keep moving the magnet around, though, or you'll have to keep recalibrating the compass. If your compass only points to the magnet, you obviously have too strong a magnet. You could also get an air pressure switch and be done with magnets. Mike *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Mon Aug 18 2003 - 22:24:21 PDT
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