Autopilot Woes

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   Hi all. I’m looking for some insights on a SimNet / NMEA Micro-C network issue that I’ve been chasing for a while.  Our boat is a 2014 Hanse 445 - it's got a mix of the original Simrad equipment and newer (2021/22/24/25) B&G replacement/upgrades that use Micro-C.
My fundamental problem is our autopilot going into standby mode.
Here's the equipment:
Jefa direct drive autopilot motor (original)
Simrad AC42 autopilot computer (original)
Zeus 3S chartplotter (2021)
Triton displays (2021)
RC42 rate compass (original)
RF25 rudder feedback sensor (replaced 2024)
Airmar DST (replaced 2022, NMEA micro-c)
B&G Wind Speed WS-310 (Replaced 2025, NMEA micro-c)
Autopilot randomly disengages in both Heading Hold and NAV.  No apparent issues on Wind.
Errors seen at different times:
AP Heading Data Missing
AP Depth Data Missing
Rudder feedback error
AP NAV data missing (other times)
Steering quality itself is now fine after tuning deadband. No thrashing.
Compass: RC42 will not calibrate.  I've tried 15+ calibration attempts.  Neighbor got a text saying a drunk person was just doing circles in the bay at 11am.  Which is ridiculous, we didn't start drinking until 11:50... but I digress...
We were in calm seas, slow steady turns and I've tried engine running, silent running  (no engine, no autopilot or chart plotter on, no other electronics except nav related).
Calibration always fails.
Heading appears plausible on displays.
Recent changes
Last spring we replaced an older Simrad / SimNet wind sensor with a B&G wind sensor that outputs NMEA on a micro-c connector.  I know on the simnet, one end of the termination is supposed to be the masthead.... I don't know if this matters.  It's been tied into our Simnet with adapters and we've been running a mix for awhile when there were no issues.
I've reseated and cleaned most SimNet connectors.
Replaced a couple of clearly bad micro-c NMEA-to-SimNet cables feeding GPS and Triton displays
Checked RF25 calibration and rudder test. Both pass
Other sensors, Zeus, and Tritons otherwise behave normally
All data appears present most of the time
Any insight from people who have debugged this would be much appreciated.

Edited by stulk75 - 08 February 2026 at 13:03

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stulk75 Members Profile Send Private Message Find Members Posts Add to Buddy List Lieutenant Commander Joined: 25 November 2020 Status: Offline Points: 72	Post Options Post Reply Quote stulk75 Report Post Thanks(0) Quote Reply Topic: Autopilot Woes Posted: 06 February 2026 at 20:54
	Hi all. I’m looking for some insights on a SimNet / ~~NMEA~~ Micro-C network issue that I’ve been chasing for a while. Our boat is a 2014 Hanse 445 - it's got a mix of the original Simrad equipment and newer (2021/22/24/25) B&G replacement/upgrades that use Micro-C. My fundamental problem is our autopilot going into standby mode. Here's the equipment: Jefa direct drive autopilot motor (original) Simrad AC42 autopilot computer (original) Zeus 3S chartplotter (2021) Triton displays (2021) RC42 rate compass (original) RF25 rudder feedback sensor (replaced 2024) Airmar DST (replaced 2022, ~~NMEA~~ micro-c) B&G Wind Speed WS-310 (Replaced 2025, ~~NMEA~~ micro-c) Autopilot randomly disengages in both Heading Hold and NAV. No apparent issues on Wind. Errors seen at different times: AP Heading Data Missing AP Depth Data Missing Rudder feedback error AP NAV data missing (other times) Steering quality itself is now fine after tuning deadband. No thrashing. Compass: RC42 will not calibrate. I've tried 15+ calibration attempts. Neighbor got a text saying a drunk person was just doing circles in the bay at 11am. Which is ridiculous, we didn't start drinking until 11:50... but I digress... We were in calm seas, slow steady turns and I've tried engine running, silent running (no engine, no autopilot or chart plotter on, no other electronics except nav related). Calibration always fails. Heading appears plausible on displays. Recent changes Last spring we replaced an older Simrad / SimNet wind sensor with a B&G wind sensor that outputs NMEA on a micro-c connector. I know on the simnet, one end of the termination is supposed to be the masthead.... I don't know if this matters. It's been tied into our Simnet with adapters and we've been running a mix for awhile when there were no issues. I've reseated and cleaned most SimNet connectors. Replaced a couple of clearly bad micro-c ~~NMEA~~-to-SimNet cables feeding GPS and Triton displays Checked RF25 calibration and rudder test. Both pass Other sensors, Zeus, and Tritons otherwise behave normally All data appears present most of the time Any insight from people who have debugged this would be much appreciated. Edited by stulk75 - 08 February 2026 at 13:03

marsella Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 21 June 2022 Location: Antigua Jolly H Status: Offline Points: 592	Post Options Post Reply Quote marsella Report Post Thanks(0) Quote Reply Posted: 06 February 2026 at 23:08
	Sounds like network problem. If you go to Zeus>network, do you see all your devices listed there at the time when the error(s) pop up?

Jojo Members Profile Send Private Message Find Members Posts Add to Buddy List Captain Joined: 03 August 2022 Location: liljeholmen swe Status: Offline Points: 166	Post Options Post Reply Quote Jojo Report Post Thanks(0) Quote Reply Posted: 07 February 2026 at 09:11
	Have you tested your simnet resistance? If you test resistance (60 ohm) the 2 pin on the right of the keyhole female connector yellow and blue. If you still experience falling and you have 60 ohm 58-61 is OK in my experience, you might have the need for a noise filter in your simmnet Edited by Jojo - 07 February 2026 at 09:11
	3 Cabin, Hanse 342, Deep draft, Tiller version.

stulk75 Members Profile Send Private Message Find Members Posts Add to Buddy List Lieutenant Commander Joined: 25 November 2020 Status: Offline Points: 72	Post Options Post Reply Quote stulk75 Report Post Thanks(0) Quote Reply Posted: 07 February 2026 at 19:27
	I have not tested the resistance. My multimeter is not working... I'm certain it is a network problem! Today I crawled through the boat and documented every multi joiner, tjoiner, device and connection type. I discovered an extra simnet style terminator (I think) and removed it. It was located at a tjoiner at the base of the mast. So cable in from nav station, then the mast cable to the wind sensor, then a terminator. I don't know if this was added when we had our B&G WS-310 wind sensor installed or if it was there from the original installation. My understanding of the original simnet only network was the wind sensor acted as a terminator at the top of the mast... but why would there be a simnet terminator at the tjoiner? Or was that how it was originally done? Does anyone know if the B&G WS-310 functions as a terminator?

Mark_J1 Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 12 March 2013 Location: Dover&Medway UK Status: Offline Points: 690	Post Options Post Reply Quote Mark_J1 Report Post Thanks(0) Quote Reply Posted: 07 February 2026 at 22:11
	Someone may have left a Simnet terminator plug at the foot of the mast so the network can be terminated without the wind sensor. Useful in situations where the wind sensor is missing or damaged. Then perhaps forgot to remove it when the new wind sensor was installed? Mark
	Hanse 400e "Grey Goose" Hull #31

marsella Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 21 June 2022 Location: Antigua Jolly H Status: Offline Points: 592	Post Options Post Reply Quote marsella Report Post Thanks(0) Quote Reply Posted: 07 February 2026 at 22:21
	If you have a network diagram that comes with the new boat, you can probably locate which branch is at fault by tracking the devices connected to it. Here is how this diagram looks for 458: https://1drv.ms/b/c/d95c2a4f8fd7b619/IQCZHiHRIun4Q6InW6hLcRggAa2_X1R8BcqxgfoeuDzOjaY

Jojo Members Profile Send Private Message Find Members Posts Add to Buddy List Captain Joined: 03 August 2022 Location: liljeholmen swe Status: Offline Points: 166	Post Options Post Reply Quote Jojo Report Post Thanks(0) Quote Reply Posted: 08 February 2026 at 10:17
	The b&g is using NMEA 0183 down the mast and then converted to NMEA 2k at the bottom using a dongle to convert that signal. From what i recall that interface do not have a terminator so you need to add one Question did you update your plotter to latest firmware as the b&g is newer I have tested that on my boat and it did not work well to my Garmin plotter so I repaired the old original windvain It was a broken cable that was the original fault so it was a fairly easy fix at the beginning that I was over solving Now it working
	3 Cabin, Hanse 342, Deep draft, Tiller version.

stulk75 Members Profile Send Private Message Find Members Posts Add to Buddy List Lieutenant Commander Joined: 25 November 2020 Status: Offline Points: 72	Post Options Post Reply Quote stulk75 Report Post Thanks(0) Quote Reply Posted: 08 February 2026 at 13:00
	I guess I should correct my original post to state "micro-c" vs NMEA, as I meant the connection types. Since I've upgraded over time from the original Simrad equipment, the network is now a mix of SimNet and Micro-C connectors. @marcsella those Network diagrams were helpful, even if not identical to my setup to help my thinking through this mess. Would be great to know if there is software out there to create our own. @Mark - I discovered that what I thought was an extra terminator at the base of the mast, was a SimNet noise filter... which apparently may not be needed anymore. My understanding is it would have been used with an older Simrad wind vane using a SimNet cable. Since I now have a B&G WS-310 with a Micro-C cable, I'm going to leave it out of the picture. So far the diagnostic screen on the Zeus is NOT throwing any errors or packet collisions while everything is powered on and autopilot is engaged. But this is on my mooring without real sailing/motoring conditions. Will be going out in a bit to try and get my compass to calibrate... Edited by stulk75 - 08 February 2026 at 15:44



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