Autohelm ST 7000 track mode problem

[LJK]

Having trouble with ST 7000 control unit in “track mode”. Waypoint data is supplied over Seatalk as RMB sentence. Data for waypoint can be reviewed on control unit (so this does not appear to be a “NO DATA” problem).

When at <5deg from course and <0.1NM crosstrack distance, I engage unit by pressing AUTO, then press TRACK to (supposedly) enter track mode. Boat appears to steer to waypoint. At the waypoint AutoPilot continues on previous course, no alarm sounds and no display of proposed turn direction. Pressing DISPLAY does however show the details for the next, new, Waypoint.

Boat has 2 control units, behaviour is the same at both controls. Alarms do sound if for instance I force "NO DATA" or exceptional cross track "OFF COURSE". System behaves without fault otherwise. "Track mode" previously worked, suspect operator error on my behalf or that I have mis-configured something (with new GPS and Chartplotter). But what? Any suggestions welcome.

thanks,

L

 

[Keith-i]

Not sure I can help with you specific problem but I had some issues with my ST6000 a while back. Presumably you have checked that it is receiving waypoint name, XTE, bearing info etc from the GPS. IIRC you scroll through the display screens and make sure there is info on each pages an no dashes showing. If that is the case then I'd be tempted to recalibrate. After going through the whole calibration process again and minimising compass error mine now seems to be behaving.
If it all worked prior to GPS change then perhaps it is a NMEA sentence problem. Mine works fine on RMB alone though.

 

[LJK]

Belatedly I have been able to get down the boat and check my facts.
I have recalibrated (odd driving slowly in a circle!) but the problem persists - the ST7000 will not enter "TRACK mode".
I reviewed the data pages you mention. I have WP name, XTE, WP distance and WP bearing. However I notice that the WP bearing is displayed as TRUE and only as true. Can you recall if your unit also displays WP bearing as MAG?
I am wondering if for some reason the ST7000 is failing to convert the RMB sentence's TRUE bearing to the MAG it needs to actually steer.

 

[jrudge]

You might also consider entering dealer mode and resetting the unit to factory.

I would also remove / disable the second control head so that you are limiting the number of variables as you try and fault find.

I would also call ray marine support who are very helpful and may point you rapidly in the right direction

 

[Keith-i]

Can you recall if your unit also displays WP bearing as MAG?
I am wondering if for some reason the ST7000 is failing to convert the RMB sentence's TRUE bearing to the MAG it needs to actually steer.

That could be your problem as rather interestingly I have a note on my crib sheet about setting this thing up that the GPS must be set to mag for it to work. I must have read it somewhere in the installation manual and noted it as being a subtle but important bit of info.

 

[LJK]

Thanks for the replies.

@jrudge – I cannot find from the manuals how to enter dealer mode or reset the unit. Clarification: my unit is a ST7000, not a ST7000+ (for which I can find description of a dealer mode). I can access “calibration” menus which configure how the AP steers but there’s no mention of a reset function in the manual. However, I will check the settings when back on the boat.

@Keith-i - Yes, I suspect MAG vs TRUE BTW is the problem.

This Raymarine FAQ post http://forum.raymarine.com/showthread.php?tid=4077 says “the RMB NMEA 0183 sentence is usually the best choice for supporting the autopilot’s Track feature when using autopilot designs preceding Raymarine's Evolution autopilots“

but it also says:

“Any Bearings need to be magnetic (preferred); otherwise, the autopilot must receive true bearings with variation in order to permit the autopilot convert the true bearings to magnetic bearings.”
This seems a bit contradictory: according to the NMEA spec for RMB, Bearing to Waypoint (BTW) is expressed in TRUE.

Nonetheless, this post seems to suggest there are two ways to communicate BTW to the ST700. Either send TRUE BTW (in for instance RMB) and the ST7000 will convert to MAG or send MAG BTW.

So, I will try sending APB from the chartplotter (which I can set to contain MAG BTW).