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Title: Wild swings on Nav—not NMEA related!
#15
fish2live Wrote:I'm driving a 48' commercial fishing boat. The multiplexer is mostly there as a convenient way to go from USB to the autopilot's rx terminal. It is also a backup route to put an alternate GPS feed into the computer.

I'm assuming the backup GPS is either not turned or not wired? No possibility that it is feeding data into the incoming stream....

fish2live Wrote:The VHF radio is a red herring.

yeah, I don't think it's the radio, easy way to verify it would be to key it and if nothing happens AP-wise, probably not the cause...

fish2live Wrote:My autopilot also has settings to control the turn rate. Those settings don't do anything to control the new direction of travel. They only control how long it takes to swing around to the new heading. Normally my autopilot does a pretty good job of turning on to a new heading. The 100°+ turn that I described in my first post overshot the new course bearing line only because of the extreme angle of turn and it corrected itself rapidly when it came back to the course line. When the problem occurs the autopilot display clearly shows that it is receiving a new heading that is way off the proper bearing. In fact, since the wrong heading is usually 40-60° off the proper bearing, the autopilot usually does a great job of turning to the wrong heading.


When you say the autopilot display shows it is receiving new heading..do you mean it is displaying the same BTW as the computer? To the best of my recollection, the NMEA sentences for Autopilot data do NOT include heading info for steering to a WP, only BTW (Bearing to WP not to be confused with the heading to the WP) An Autopilot in "Nav" mode steers to a WP using crosstrack, not heading. It may or may not, depending on the SW residing in the AP itself, use heading info to increase or decrease rudder in order to null crosstrack.

I would suggest experimenting with the rate of turn control. I think that what is happening upon receiving the new WP, the AP is oversteering to come onto the new course.

Lastly, what version of MacENC are you running? Older versions (much older) dealt with new waypoints in routes in a manner that would explain perfectly what is happening...
 
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