Compass bearing mismatch

[DougM]

Here is an interesting phenomenon: I have a Raymarine autopilot, RS125 GPS, and a C70 display. If I turn on the autopilot only, the compass bearing on the autopilot display matches the binnacle heading within a degree or so, If I switch on the C70 at the same time, it shows shows a compass heading that matches the binnacle heading. However, the heading on the autopilot goes awry by 90 degrees, and the C70 display shows the boat icon traveling sideways along the compass heading. Then if I power the autopilot off, the boat icon reverts to pointing in the direction of travel. I have never seen this happen before.

Short of recalibrating the autopilot compass, I cannot think of a remedy. Has anyone got any better solution?

 

[Jackdaw]

It sounds like turning on your C70 is creating a magnetic field that is screwing up the compass in/attached-to your AP. The C70 is getting HEADING information from the AP as well, so even it knows your GPS course, it correctly shows your heading as wrong.

 

[kloudie1]

C70 or more likely the power wire that feeds the C70 is too close to the autopilot Flux gate sensor??

 

[DougM]

Jackdaw, Kloudie; neither case seems very likely. The boat has had these systems working well together since new in 2005. The flux gate compass is not near the autopilot computer box, connections are tight and cables do not run that close to one another to consider any kind of interference. The only linkage is the seatalk cabling. GPS position on chart is accurate.

I will grant you the fact that the proximity to the binnacle is not ideal, but the way the instrument pod is set on the pedestal governs that. Chalk that up to a designer with little knowledge of potential interference and a need for aesthetics. If I could figure out another place on the boat to put the chart plotter and still be able to see it , I would.

 

[Bill Roosa]

So it worked correctly and just started having kittens?
I'd have to agree with Jackdaw the C70 is causing interference with the fluxgate compass. When you turn off the AP the C70 uses the GPS heading (bearing to be navigationally correct) instead of the fluxgate.
Since it was working correctly ask yourself what have you done near the fluxgate lately. All current carring wires make magnetic fields so if you recently installed an electrical appliance turn it off and see what happens.
I'd also agree that recalibrating the fluxgate is not needed as it seems to be working correctly when it is not being interfered with.