[CA] Keeping Autopilot in use without Raymarine MFD

Hi,

I have searched for information but have not found the answer.

I have a perfectly good Raymarine Autopilot system on my Nordic Tug 37 (Raymarine Smart Pilot S3G with ST 8001 Control head). It is connected to a Raymarine Fluxgate Compass that is working well. The Autopilot works extremely well even in rough following seas that are a challenge to steer manually. I would like to keep the Autopilot in place and running.

I am replacing the my Raymarine E120 Classic MFD, the Raymarine (?Raystar) GPS, and the accompanying DSM 300 and analog radar. I am replacing the E-120 system with a third party MFD and third party radar.

Other sensors/devices in the system:
1. Airmar 150WX providing GPS and heading information in addition to weather & wind etc.
2. Airmar H-2183 Fast heading sensor giving 10-20 Hz heading values via NMEA 2000
3. Vesper XB-8000 AIS providing GPS and AIS data and also acts as a NMEA 0183 - NMEA 2000 bridge to a Brookhouse iMux channeling 0183 data.
4. I plan to have the Cummins Engine data streaming to and from the new MFD via 0183.

I can have GPS and any other 0183 data ported to the Autopilot via the iMux or from the third party MFD's 0183 OUT port.

Since I am removing the E-120 MFD. How do I keep the Autopilot running as well as it has been without the E-120 in the system? (Before removing the E120, if I tried starting the Autopilot without the E120 MFD powered up, I would get a "Seatalk Fail" Alarm. How do I avoid this?)

What components of the current system do I need to keep? (I do not actually care if it receives instructions from the new MFD, I just want to be able to dial in a heading and have the boat stick to that...)

Any suggestions or insights greatly appreciated.

Thanks.

-evan