Mounting Fluxgate Compass in Aluminium Yacht

[noelex 77]

Any problems with mounting the fluxgate compass in the mast will come from the wires running up to the masthead, or ferrous components in winches etc that are mounted on or close to mast. The aluminum mast section on its own will not cause any (practical) deviation.

[David M]

This is not as complex as it is being made out to be.

Aluminum does not influence a magnetic field, unless it has DC current running through it. Anything with current running through it does have a magnetic field unless it is AC or DC wrapped around the negative and positive conductors...and even then there will be some magnetic influence.

You DON'T want to put a compass where there is DC current flowing, like a mast that has wires running through it unless you don't mind seeing two different headings when your mast lights are on versus when they are off. Or you dont mind seeing your heading reading swing wildly when you transmit on your masthead antenna.

Put the fluxgate below deck as far away from the iron engine and DC wires as you can get it. Being as close as possible to the boats center of buoyancy is not all that critical...getting it way from DC wires and the engine is very important in you want minimal corrections to you fluxgates deviation table. Deviation table corrections outside of 10 degrees are generally considered unacceptable.

[chala]

Originally Posted by hellosailor

But guys, there's a simpler empirical way to answer this question. Take a modern smartphone

Or also any fluxgate compass etc.

Originally Posted by noelex 77

Any problems with mounting the fluxgate compass in the mast will come from the wires running up to the masthead

Originally Posted by cal40john

If two wires are close to each other with currents flowing in opposite directions, they make opposite magnetic fields that tend to cancel each other. Twisting them does the job better.
John

Originally Posted by noelex 77

or ferrous components in winches etc that are mounted on or close to mast.

This is taken care by the automatic compass deviation correction.

Originally Posted by noelex 77

The aluminum mast section on its own will not cause any (practical) deviation.

Yes it will.

Originally Posted by chala

Mast or vessel both will make a change of reluctance following a change of direction.

Magnetic reluctance - Wikipedia, the free encyclopedia

Originally Posted by David M

Deviation table corrections outside of 10 degrees are generally considered unacceptable.

See manufacturer recommendations.

Note that the manufacturer recommends 1.2m from the steel deck at the stern railing. I have found that 0.6m work all right making a good compromise between ferrous object and height above the roll centre.

[hellosailor]

Chala, I suggested a smartphone because they're more common than "spare" fluxgate compasses. And the software will usually show you analomoous magnetic fields in one-tesla readings, rather than letting you try to figure out how your degree readout is quivering.

Real sailors still use sunstones. All this high-tech magnetic compass stuff is totally unreliable. <WEG>