Fluxgate compass

[Des_Beechey]

I have a steel yacht with fluxgate compass as part of the autopilot system. Does it display a heading in degrees magnetic or degrees true?
I have just had the main magnetic steering compass professionally adjusted, and am now trying to get the fluxgate compass right. I have two ways of adjusting the fluxgate:
1. Auto adjustment, by putting it into adjustment mode and going around in a circle, which I have done.
2. If there is still a constant error, rotate the fluxgate circuit card in the fluxgate unit.
At the moment, the fluxgate gives the same numbers for heading as the magnetic compass. Is this what it should do? If so, this implies the fluxgate reads out in magnetic. Or should it differ from the magnetic by the variation (13 degrees east for here), in which case the fluxgate is showing a constant error of around 13 degrees?



Des Beechey

 

[kimhollamby]

Depends on the display it is connected to. You can usually programme the display to show in mag or true, so check the manual and look for user settings.

If you have managed to get the ship's compass and fluxgate to agree, that's a great start. I'd leave the actual fluxgate itself alone at that point.

 

[peterb]

Your fluxgate measures the local magnetic field. In the absence of boat-induced deviation, it will give you magnetic bearings.

Most fluxgate compasses include a cunning scheme for measuring boat-induced deviation and allowing for it. Again, this should result in the compass giving magnetic bearings.

Some fluxgate compasses (via a GPS link, usually) can use a pre-stored map of variation to convert the magnetic bearing into true. But it's still the magnetic bearing that is measured.

I would take Kim's advice; if the two agree then don't try to change either. Decide which you intend to use as your primary instrument (I'ld go for the swinging card version, as having less to go wrong) and use the other as a back-up and as a source of periodic checks.