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Sheldon Haynie

"Compass Safe" & Optimal sensor design.

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Having an email exchange with a major Marine electronics vendor's support staff, as they sell a VHF handset that looks interesting, and claims inductive charging from a 12V DC starting power. That would infer that they have to create some type of varying magnetic field to couple across the airgap, and my question of them was what was the distance to my compass(es) needed to be safe from their device.

They responded somewhat off the cuff that the 'industry standard" was 1 meter, (though their VHF console only requires 1 1/2 feet). Not sure where that came from, nor on reflection that it's a simple answer. I would like to have the charging cradle on a navpod at the helm, so that I would have a convenient Radio while steering..

My default navigation compass is mounted in a binnacle ahead of the wheel, and has been deviated every time I add major gear. My new electronic compass will self correct if given a few slow circles, but that's only for the magnetic state at the time of the correction.

I do have a rotary drive mounted almost directly below the compass and about 6 feet lower, that is fed by 15Amp DC and would be changing as the Autopilot works. I envision a feedback loop that I had not previously anticipated. and will have to see if that changes the compass reading while the boat is stationary.

Given a terrestrial Field of about 250 milliGauss (25 uT for MKS) what level of field do I need to stay below, and does it matter if the field is in plane of the sensor as the prospective handset would be, or is orthogonal as my autopilot drive is?

A related yet separate issue is the placement of the fluxgate and GPS sensors, previously they had been aft to be quiet and out of the way, not vulnerable to being broken or having a can set adjacent. Now thinking that placing them closer to center of mass/moment and turn/buoyancy makes a lot more sense to get quality signals, and minimize the amount of jitter on the MARPA, and overlay. (though the radar will be mounted aft on mizzen.

Any thoughts?

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