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Wings

Hello, Derek,

Your suggested solution for the autopilot was spot-on. I disconnected the SPX30-to-Seatalk-bus cable and the autopilot system is now functioning correctly, as before. It behaves as a standalone unit, but that's entirely acceptable. Thank you for your help.

Once the SPX30 was disconnected from the other instruments (Classic C80, ST60+ Wind/short arm transducer and ST+Graphic Display) some of the ST problem in these other instruments disappeared. We could again "see" more types of information on the graphic display, for instance. This seems to imply the problem was in the AP system, and that's disconcerting. Should I suspect a fault in the autopilot system itself, or in the connection between the AP system and the Seatalk bus?

I'm taking the liberty of asking another question related to these others. Our venerable C80 MFD works well but position and heading functions are still misbehaving.

We have read the C80 manual and have learned that the GPS sends heading and position information to the C80. With position data only, the C80 displays boat position as a solid black dot, and with heading provided, too, the vessel is presented as a ship icon. Our C80 is now losing the heading information that's provided by the GPS. In other words, we see a black dot in the correct location, but not a ship icon. In addition, the Graphic Display does not display a heading.

The C80 does display the COG, though, and that's being forwarded to the ST bus since it displays on both the C80 and our Graphic Display. No heading, but COG. We have both a numeric COG read-out and a two-arrow green vector. We do not have a one-arrow heading vector. How can the GPS or C80 find the COG and not know the heading? The manual is quite specific that the GPS provides position and heading information. Is COG is being "derived" by the C80 by looking at position information only (i.e. without heading information) at two different times?

Our reading of the C80 manual and our experience tell us that heading is the direction the boat's bow is pointed, while COG is the direction the boat is traveling over the ground, a GPS-based value. Are we wrong in that understanding? How is the heading information being generated?

I've cleaned and returned the GPS yellow data wire on the ST bus, but it didn't help. Periodically, the C80 "No Heading" alarm sounds, and the ship icon changes to a dot. Periodically, the "fix" icon in the upper right changes to "no fix" and our position disappears from the screen.

I have captured the GPS data stream but don't know what I'm seeing other than our Lat/Long, evident in the GPS sentence. I've enclosed an image.

We're at a loss on the next step. If you discern that the GPS is failing, and I think that it's possible since we're using losing position and heading data, can we use the info from a standalone AIS system? Shouldn't the sentences be usable by the C80?

Thanks for the help, as usual.