S1G Fluxgate Compass Alignment Drifts - Use External Compass?

[Bill Kneller]

Problem: When engaging S1G Autopilot there is sometimes a course jump a few degrees.

Diagnosis: The S1G course computer is connected to a Type 1 drive, a Raymarine fluxgate compass and rudder sensor. It is also interfaced via a Seatalk to Seatalk NG converter to a Nexus multi-axis compass used for my instruments (Nexus & B&G) and Raymarine e97 & e125 multifunction displays. The MFDs are set to use the Nexus multi-axis compass which has a 10 Hz update rate. Per the manual, the S1G defaults to the Fluxgate compass over the heading received via Seatalk since the Fluxgate compass is connected. Interconnections diagrams are at this link: http://j109.org/forum/download/file.php?id=44

The Nexus compass is very accurate and responsive. The Raymarine compass appears to drift a few degrees over time (weeks). When the Raymarine and Nexus Compass read the same value, there is no course jump when the Autopilot is engaged. If there is a difference between the two compass readings, there is a course jump when engaging the Autopilot. I can adjust the Raymarine fluxgate compass so it tracks the Nexus compass every few weeks, but this is inconvenient.

I notice in the S1G manual that the course computer will accept a NMEA or Seatalk compass and if it is used, the fluxgate compass should be disconnected.

Questions:
1. Will the S1G perform as well using an external Seatalk connected compass (actually Nexus HPC multi-axis compass over NMEA 2000 -> Setalk NG -> Seatalk)?

2. Can the Raymarine Fluxgate compass be disabled by removing only a single lead (e.g. power or ground), or does it require that all leads (power ground and coils) be disconnected from the course computer?