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Old 02-28-2018, 04:18 PM   #19
twistedtree's Avatar
City: Gloucester, MA
Country: USA
Join Date: Jan 2013
Posts: 4,969
Originally Posted by Maerin View Post
Not so. Your ST6001 is not determining the width of anything, it's a controller. Your chartplotter is setting the steering commands, and relaying them to the course computer via the NMEA link. If your AP is off 100 ft, there's something not right. My S3 autopilot will reliably hold less than 20 ft of cross track error, close quarters/ inland/ at sea - has little to do with it.

Check to see how often your chartplotter is refreshing the data to the AP, and see if you can decrease the refresh, say from 2 sec. to 1 sec. Also, check to see what sentences are being sent. If you send all of them, you'll jam up the bandwidth of the NMEA bus, and likely create a data loop that prevents the AP from responding smoothly. Best to start very lean, then turn on only those sentences that it actually needs to function. Start with APB, RMC, VTG. If you want to view other data on the ST6001 control head, that data may have to come from the NMEA link between the chartplotter and the AP. Again, it's helpful to turn on only those sentences that are actually needed.
I'm not familiar with the Ray AP, but most will display the current cross track error that it gets from the chart plotter. If the cross track error is small, then suddenly gets very larger, then you have a communications problem between the AP computer and plotter.

When working correctly, the plotter will update the cross track error (XTE) every 1-2 seconds, and you will see it gradually getting larger and larger on your AP display.

If the AP display shows XTE growing, but the AP isn't taking any action to steer back to the track line, then you have an AP problem. As previously mentioned, many APs have a setting for the allowable cross track error before it starts to take corrective action. From the sounds of it, this is most likely where you problem is. Every pilot process all the inputs a bit differently, but a number of them can effect the behavior. Rudder deadband, gain, rudder position indicator, etc can all have an impact. Air in your steering can also have a big effect, as can any other mechanical wear in the steering mechanism.
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