711C Drifting off course

711C Drifting off course

Postby Catmando » Tue Aug 29, 2017 5:55 am

I have a 711C that continuously drifts off track to the East while in Nav/Course mode with no wind or current. If I change to XTE Precision the AP seems to be fighting the drift and I get a lot of rudder activity/swinging around the course line. In Auto (not advanced auto) mode, (setting course using Heading To Steer) the boat will track perfectly straight to the WP with only occasional 1 degree course corrections and very little rudder activity.

PG-700 shows Heading that is usually 5-7 degrees off my COG (again with no wind or current). Adding in compass offset seems to help but the further I travel North or South changes how much offset I need. Re-calibrated the PG-700 twice and have sea state set to full/auto. Not sure what else to try so any ideas/thoughts would be appreciated.
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Re: 711C Drifting off course

Postby Melville » Tue Aug 29, 2017 8:01 am

What MFD/plotter system is driving the pilot in nav mode?
What do you have set for the XTE limits?
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Re: 711C Drifting off course

Postby Catmando » Tue Aug 29, 2017 8:13 am

Thanks for the reply Melville. I have two TZT2 15's, one of which I typically use for Navigation. Not sure what value is set for XTE limit (probably default). Is that configured in Settings? I will check.
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Re: 711C Drifting off course

Postby Catmando » Tue Aug 29, 2017 8:54 am

If I am looking at the correct setting the XTE Value is 67 Yards
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Re: 711C Drifting off course

Postby Melville » Tue Aug 29, 2017 9:50 am

The XTE setting is under the route set up. 67 yards means the boat can drift up to 200' left or right of the course line when in Nav mode. Try bringing it down.
Also, please check that you have these PGNs turned on in the N2K output.
129283, 129284, and 129285.

Let us know if this helped and if not we can investigate further.
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Re: 711C Drifting off course

Postby Catmando » Mon Sep 18, 2017 5:43 am

Thanks again for the reply. I adjusted the XTE and verified PGN settings which helped but the AP still shows a lot of rudder activity and drifts on every few minutes makes a relatively steep turn to get back on course. If I switch the Nav setting to Course mode the boat immediately starts to track to the west again (sorry, I meant west in my first post) at a rate equal to about 5% (.05 miles for each mile traveled).

It is only in Nav mode that I get this behavior. In non-advanced Auto mode I can get it to track to WP on an exact line with minimal rudder activity. That is once I figure out how to get the right course which is usually not the same as the WP bearing.

Appreciate any other pointers
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Re: 711C Drifting off course

Postby Melville » Thu Sep 21, 2017 9:22 am

Before you start to navigate to a selected point do you hit the course line, select restart, and then select Nav on the 711C.

The XTE message that is output begins when you call up a destination point. if you travel a distance before engaging Nav it is trying to get back to that old rhumb line.
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Re: 711C Drifting off course

Postby Catmando » Fri Sep 22, 2017 8:37 am

Thanks Melville. Yes I hit restart after aligning to course line, and engage AP from TZT. Just to be clear the following is going on:
1) AP will hold the rhumb line (while in precision Nav mode), but seems to only do so with a lot of rudder activity.
2) In Nav/Course mode the rudder activity is much lower, the boat tracks in a fairly straight line but constantly/significantly drifts West off of original rhumb line (on North or South heading) with no wind or current.
3) In Auto mode (not advanced Auto mode), the AP will hold a near perfect line to WP with almost no rudder activity providing I adjust the course East of WP bearing
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Re: 711C Drifting off course

Postby Melville » Sun Sep 24, 2017 6:14 am

Cat-
Let's look at some basics and see if there might be a set-up issue.
Next time you are out please get up on plane or cruising speed and steer a dead on straight course, hopefully in some flat water. With the pilot in standby does the rudder angle indicate 0?

At the dock turn your wheel hard over port or starboard. Then slowly and smoothly turn it hard over the other way. Are you seeing any jumps in rudder angle reading or lags where it stops and catches up?

Finally let me know if your Net Towing mode is on or off. And if you have a chance see what affect turning setting it on or off has. (I realize you are not towing, but on allows the pilot to take the current rudder trim into account when going into auto)

BTW- Precision in Nav mode will always cause excessive rudder movement. In heavy seas and open water it is actually more efficient to use economy.
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Re: 711C Drifting off course

Postby Catmando » Mon Sep 25, 2017 5:47 am

Thanks again Melville. I did reset rudder center but admittedly did so off plane. Will reset at planing speed to see if that changes anything. No jumps in rudder angle readings while helming over, smooth as can be. Will check for Net Towing mode and will report back.

Yes I get that Precision results in more rudder activity. I guess what bothers me the most is the level of cross track in Nav/Course on calm days with no waves/wind/current. And I suspect whatever is causing that is driving excessive rudder activity in Nav/Precision (including occasional large swings in course). My last AP (511) did a flawless job at holding the line in worse conditions which is why I am suspect something is off here. Let me do some additional checking and report back.
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