Simrad problem

[spudsdailey]

I have a Simrad AC 42 and an AP48 head unit. The chartplotter is a new Furuno TZT 14.

I am having trouble getting the two to communicate properly. As an example, when I Navigate to a "Go To" the auto pilot steers initially 25-40 degrees off target; then over a minute or two, it locks on to the proper bearing and is fine for the duration. Tried to re-calibrate; nothing works.

When I ask it to "Auto" course, it is fine; steers a perfectly straight course.

Any thoughts.

[Dsanduril]

Does the chartplotter heading agree with the AP heading? I've had the same problem with a different brand of AP. In that case the chartplotter was sending a BTW and the AP automatically turned to that heading, but the AP compass and the heading in the chartplotter didn't agree (a lot of times when I use 'Auto' I don't care what the 'heading' is, so never really bothered to check that calibration - as long as it steered straight I didn't care what the AP heading said). The AP had a calibration routine to align compass to GPS.

Another option, which I have also seen in other units is magnetic vs. true bearings. If the chartplotter is sending one and the AP is expecting the other it will give you a turn about the same as the variation for that location.

[spudsdailey]

Thank you for the note.
Yes, the chartplotter heading and the AP heading are the same, both in magnetic.
Could this be a malfunctioning fluxgate?

[Shoalcove]

It been a while, but when I installed a Raymarine e125, my AC42 had some issues recognizing some PGNs that appeared priorized by the e125 but seemingly not preferred by Simrad. I’m not a computer guy so may have the reasons incorrect but there was an issue. I ended up deep in the menus to sort things out and now the combo is flawless. Is it possible that for “go to” the AC42 is using incorrect heading info (ie.from a gps source rather than compass)? In my case, the problem was what the AP was using as a data source and it was in its menu where I found the solutions.
Good luck!

[spudsdailey]

Furuno says just turn on two PGN outputs: Cross trak error and gps navigation.

I have tried others to no avail.

[Shoalcove]

My issue wasn’t with the plotter but rather what the Simrad was reading. I’d give Simrad a call. I’ve found them very helpful in the past. Good luck with it!

[billknny]

Originally Posted by spudsdailey

I have a Simrad AC 42 and an AP48 head unit. The chartplotter is a new Furuno TZT 14.

I am having trouble getting the two to communicate properly. As an example, when I Navigate to a "Go To" the auto pilot steers initially 25-40 degrees off target; then over a minute or two, it locks on to the proper bearing and is fine for the duration. Tried to re-calibrate; nothing works.

When I ask it to "Auto" course, it is fine; steers a perfectly straight course.

Any thoughts.

That is actually not surprising, and is "expected" behavior.

What the AP is doing is quickly bringing the boat to be on top of the EXACT rhumb line between the starting point and destination.

If your boat is EXACTLY on a straight course toward the destination, that initial deviation will be smaller, but still will happen--at least a little--as the AP figures out what heading is required to maintain the boat within 50 feet of the rhumb line course.

(Depending on your AP brain the "rhumb line" course might actually be a great circle, but the concept is the same.)

[tanglewood]

Try resetting cross track error (reset XTE) immediately before you enter Nav mode on the AP. Also observe the reported XTE as reported by the pilot. It should be very small.