Chart plotter issue

[Fishpants]

Hi all,
I have a 2016 Ranger 29S. On my Garmin chart plotter I’ve recently found that even when set to “heading up”, the blue heading line is way off, and the boat icon is facing up. I can’t seem to correct this unless I do a compass calibration, which still doesn’t correct it 100%. Wondering if it’s some sort of interference with the Garmin compass? If so, is this built into the unit, or is it mounted externally somewhere. (If so, where?)
Would love some thoughts on this. It’s a pain to have to regularly recalibrate.
-David

 

[Full_O_Fish]

On the chart layers there are options for the following extensions from the vessel... Heading line (hdg), Course over ground line (cog), both hdg/cog.

Hdg comes from the autopilot compass and its calibration and is what aligns the vessel icon on the chart, while the cog comes from the internal or external gps antenna source and displays the actual direction of travel. If there is current or wind the hdg will not match the cog as the vessel is actually "crabbing" more or less depending on the speed of travel relevant to those external forces.

A cog extension line is useful for determining where the boat will actually be in a certain time or distance if answering stays the same, which is great for determining set and drift.

A hdg extension line just shows which way the bow is actually pointing and is useful for aligning the compass and radar overlay.