Simrad autopilot weird behaviour

[Shuggy]

I installed a Simrad AP44 course computer and head unit, linked to my B&G Vulcan MFD a couple of years ago. It works brilliantly. I have one niggle. When I ask it to go into 'Nav' mode and navigate to a waypoint on the MFD/plotter it initially goes batsh*t mental and offers up the weirdest heading, often 40 degrees off where it should be heading. When I click 'accept' it makes a wild course correction and I then jab my finger at 're-start' on the MFD about 10 times until it relents and goes back to a sensible heading. Then it behaves impeccably. It does this every single flipping time I use the 'Nav' function. It doesn't do it on Heading Hold, No Drift, Wind etc. I will contact Simrad but before I do I wondered if anyone else has this problem? Everything else is just great - fluxgate compass behaves with the right heading all the time, all other functionality is fine. I'm baffled! Particularly as once my fat finger has jabbed 'reset' on the Vulcan a few times it settles down and is as good as gold.

Just to be clear - although bits of my NMEA 2k system are mix'n'match, the B&G/Simrad MFD, GPS, steering sensor, head unit and course computer are all the same make and are on an uninterrupted NMEA 2k backbone. The wind and depth instruments are Raymarine and are interfaced through a Raymarine Seatalk-NMEA 2k interface. I don't believe this is the issue.

I installed all of the wiring and kit myself so I know it intimately. The rudder angle sensor is perfectly aligned and everything has been calibrated as per the book of destructions.

I can live with this foible but it never fails to amuse us when we hit the 'Nav to waypoint' mode and career around wildly for about 20 seconds. My wife thinks it always goes to starboard but I think it always points to the nearest bit of rock!

 

[Skylark]

Not 100% sure but I recall something similar happening with my Simrad NSS12. Where is the cursor when you engage the autopilot? It needs to be at your boat, done by pressing “clear cursor”. Otherwise, iirc, it wants to steer towards the WP from the current cursor position, not the boat position.

 

[Shuggy]

Not 100% sure but I recall something similar happening with my Simrad NSS12. Where is the cursor when you engage the autopilot? It needs to be at your boat, done by pressing “clear cursor”. Otherwise, iirc, it wants to steer towards the WP from the current cursor position, not the boat position.

We always 'clear cursor' so I don't think that's the issue.

 

[jwfrary]

Software on your NSS and autopilot is up to date?

You could rule out the other components of the network by shortening the back bone temporarily. Disconnect everything except the plotter compass and autopilot and try it.

 

[lustyd]

I may have missed it, but what heading sensor do you have, and is it correctly configured and calibrated?

 

[Shuggy]

I may have missed it, but what heading sensor do you have, and is it correctly configured and calibrated?

It's the Simrad fluxgate compass that came with the autopilot pack and it works perfectly - all configured and calibrated.

 

[Skylark]

@Shuggy have you tried Simrad on-line tech support? I’ve used this resource a few times and always had a good response.

 

[RichardS]

My Raymarine system used to behave in a somewhat similar way when I inadvertently set up a data loop whereby the GPS data was being sent into the plotter and then sent back out again and then going back in and setting up the loop. It happened after I connected up my AIS unit and DSC VHF with GPS input along with a multiplexer. Once I realised what was going on I was able to turn off the re-transmit GPS data function and everything started working properly again.

Richard

 

[Shuggy]

@Shuggy have you tried Simrad on-line tech support? I’ve used this resource a few times and always had a good response.

That's the next port of call. Thank you.

My Raymarine system used to behave in a somewhat similar way when I inadvertently set up a data loop whereby the GPS data was being sent into the plotter and then sent back out again and then going back in and setting up the loop. It happened after I connected up my AIS unit and DSC VHF with GPS input along with a multiplexer. Once I realised what was going on I was able to turn off the re-transmit GPS data function and everything started working properly again.

Richard

Thanks - I don't think it's that as the GPS data comes from the MFD (which has an integrated GPS). The AIS GPS is separate.