[jclark003]

Ok that makes more sense now. The gps tells your chartplotter where you are, your course over ground (cog), speed, etc. without a gps fix your chartplotter is lost. It's actually a little surprising your boat icon and chart information moved at all.

Heading data comes from the heading sensor and is primarily used by the autopilot to steer. The autopilot also uses gps data such as cog and speed to adjust for cross track error, etc. additionally the heading sensor usually gets magnetic deviation data from the gps which corrects heading Based on position.

What does his all mean? If you have bad or no gps data you are much better off with paper charts.

If your electronics installation is relatively new and you are seeing funny things happen like sensors dropping offline inadvertently you may have issues on your network. NMEA2000 networks have very specific power requirements especially on the ground and shield side. A very high percentage of electronics installation issues come from power and cable issues.

Your chartplotter installation manual should have a section on network installation and troubleshooting. That is usually a good place to start. Maretron.com also has some good data to help understand how these networks function and where to identify issues.

Good luck