Autopilot Track Following

[RobbieW]

Hi Folks,
I'm trying to figure out why my autopilot swings 0.02 Nm either side of its desired track without settling on the inputted track from the 'in use' OpenCPN route.

The background is that I have recently switched from MaxSea (it finally broke on XP) to OpenCPN, which I've used off and on for about 18 months. I had recently discovered that on the new (to me) boat I could set up MaxSea to recieve GPS input from the GP32 and output commands to the Raymarine S3G autopilot, thus the autopilot would accurately follow the 'in use' route in MaxSea.

Having switched to OpenCPN (initially 2.3.1, now 2.5) the autopilot now hunts as described in para 1. I'm not pointing a finger at OpenCPN but at the moment that change seems to be the point where things went awry. The boat used to 'wind follow' accurately with MaxSea in use, that too started to hunt at about the time I switched to OpenCPN.

Having read these forums a bit, I should say that the GPS input and autopilot output are both on COM1. I have tried a couple of suggestions from the forum to gain some insight into the scenario. So, I've tried adding the RMC message to the autopilot output - no difference. I have AIS input but that comes in on COM5 from a NASA AIS Engine, nonetheless I defined my GPS input port as an AIS shared port - on my system it seems to do exactly that and shared COM5.

Today I tried using a GPS mouse on COM4 instead of taking GPS input from COM1 and doing some wind following which worked perfectly. I have not yet been able to try a track follow with the GPS input separated from the autopilot output.

At the moment I'm thinking that the shared COM1 setup is where the problem lies? I dont seem to have the option of making this a shared AIS port as thats not where AIS input comes from but that seems to be the pre-req for port sharing in OpenCPN.

The way the boat is wired puts input and output on COM1 using an Actisense PC-Opto-1-A NMEA/RS232 adapter. If I can find the button to add a document about the wiring I'll do so, but bear in mind this documents what is inside a connection box not what the function of each pair of wires is at its functional end!