Every now and then, Blue Opal’s SeaTalk gear would boot up and display a ST FAIL message on the autopilot control at the pedestal console. I’ve never been able to work out what it was, and the old trick of “turn it off and back on again” would clear the message.

This weekend, while fiddling with the new GPS antenna and trying to get it to run through the ShipModul, I noticed that I hadn’t connected the ShipModul ground wire on input 1. This goes to the shield/ground on the SeaTalk bus.

The ShipModul uses an opto-isolation setup internally, so there was probably noise on the bus. Given I had installed the ShipModul very shortly after buying Blue Opal, I never connected installation with the problem. The ground/shield is now wired up properly, and hopefully that fixes things.

As a note, when using a ShipModul with iNavX, make sure Location Services use is turned off in iNavX if you’re trying to get the GPS data from the GPS attached to the ShipModul. iNavX doesn’t appear to be smart enough to go “hey, you asked for location services, but they’re off so I’ll tell you that and fall back to the NMEA data” – it just tells you location services are off.

Solving intermittent SeaTalk failures
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