I checked that nothing was interfering with the fluxgate compass and drew a blank.
Could be the compass and still could be interference
. They can go bad and things can change. You can notice errors in the compass by 90 degree quadrant usually if the compass is bad. In flat water
do a large slow circle and see what the ships compass heading reads vs. the fluxgate reading. Do it clockwise and counter clockwise several times. Try straight line courses and compare the GPS
reading to the fluxgate. It helps to have someone watching one compass as you call out the fluxgate numbers. Watching the two yourself and steering
the boat all at the same time can drive you nuts. Make written notes and try to repeat anything you think is a problem.
Another trick is to disconnect the compass from it's mounting and leave it connected and powered. Turn it by hand in small increments going clockwise then counter clockwise while in the slip. It should be possible to see the reading become in error if it is the fluxgate compass. You may need an assistant to do this too.
The last issue is calibration. The calibration of a fluxgate stores a table of degrees and the plus or minus deviations. The calibration process builds this table by making you run in circles. It then knows you are in circle mode then it can compute what should be the headings from what it sees. This accounts for the magnetic deviation on the boat. If that table gets trashed in the memory of the computer that can cause errors like you see too. Re calibration might fix it or there may be an electronic problem and it gets trashed again or never stores properly.
You can't see interference
so you can't know for sure it's not there. You have symptoms that could be interference so don't assume it's not. It took me days to find that out. The above will prove it one way or another. There should also be extra cable coiled up on the fluxgate as they don't always cut off the extra. Try moving it and see what happens.
So far none of this will cost you any money
, you won't break anything, and you might find the problem with some certainty. After that you need to start swapping components or pull the whole thing out and bench test it. That process is expensive and time consuming. Swapping out parts
is expensive since you can't return them if the part you swap is not the problem.
I went through something like this with a Simrad
unit in the last boat. In the end it was not the compass. the compass was fine everything was fine. The compass was getting interference and we never found out what it was since there was nothing near by but moving it to a new location worked. The autopilot
only ever worked in calm conditions and had been installed improperly by the original owner. On paper the install location for the compass was a great choice but in practice there was interference since we proved it. The problem was masked several ways. The original owner had a defective piston in the hydraulics and the second owner found that. I had a problem with the hydraulic motor
and eventually fixed that. That eventually led to a problem where the calibration would fail always. Mechanical problems hid the installation
problem for a long time. Everyone always assumed there was no interference. Odd stuff happens. Hope for a cheap