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Cheers, rigger. That was how I understood your description. So on most small yachts, especially with a bulkhead mounted compass, this method would be difficult/impossible unless you are using a pelorus? In this case I'm guessing that the method Slacko is thinking of (running multiple transits) would be more appropriate.

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Bugger the deviation card, there's bound to be a iPhone App that will do it for you.

 

Big Steel I used at Xmas uses the 4 rod magnet system, works very well on the total top to bottom steely. Having issues with the autodriver compass though and that's a fluxgate, the bastard thing.

KM I have been playing with my Fluxgate compass on fusion and have the best results 2m up the Mizzen mast and the gyro directly in line below on the bulk head a water level. The performance has been greatly improved in a following sea.

Don't think it's environmental causing the issues on Big Steel, more than some uncooperative 1's and 0's.

 

Transits are easy and if you are in the Nth Head to Compass Dolphin area there's shite loads of handy ones.

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My auto pilot, fluxgate is inside the boat, but centred on the timber mast support. It works very well. Most companies recomend that their fluxgates are mounted at least 2M above an all steel boat....

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You could of course biuld a giant Degaussing coil and drive your boat through it. Careful, you might come out in a different time though :wink:

But when ever you do maintenance to the steel Hull that requires welding or hammering, you will have to do it all over again :think: What about rafting up to another steel vessel for the night? Then what about sailing over magnetic variances in the rock below. The sounds are full of it. I imagine the Iron sands on the Westcoast are a nightmare. Then you have the Aurora at it's strongest. It's a wonder anyone can navigate anywhere accurately using a compass. :lol:

The easiest is to use an Electronic compass and then set you magnetic variations off it, AFTER you have tuned the electronic one of course. Which happens automatticaly during a 360.

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OK, a magnetic compass is a little bit of metal that aligns with the earths magnetic field, so someone explain to me how an electronic compass works???

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Similar thing squid. But instead of the little metal doodacky, it has a series of very sensitive sensors. It used to be the Fluxgate, which is a fairly large device when compared to the modern stuff. Now there are solid state gadgets that are very small and can be fitted to items as small as a wrist watch. I had one of the Casio's till it went overboard. Must get another some day. It was fantastic. All you had to do was push a button, spin the thing around in a circle a couple of times and it was sync'd. Just like setting in the older AP's on boats. Do a 360 or two while it is in a set up mode and it's done. It works out all the errors.

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More to the point. How does spinning an electronic compass through 360º calibrate it? We can't do that with a good ol' magnet floating in liquid so why does it work for an electronic dohicky?

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OK, so I've answered that question well enough for my own curiosity using Google. Came up with this, that gives the general idea without getting too technical.

 

http://www.safety-devices.com/how_compass_works.htm

 

My take from this is that the electronic doohicky can measure the distortions in the magnetic field and can calibrate from that. It doesn't just indicate a simple direction like a magnet does.

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I has a search and found a unit that uses magnetic field sensor chips that can detect the earths magnetic field.

2 of these mounted 90 degrees from each other in the horizontal plane can then be used to do the trigonometry to calculate the magnetic orientation of the circuit board.

$79.75 +P&P from Superdroidrobots.com :D

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