[CA] SPX30 Doing Poorly in Track Mode

[DSanduril]

I have an SPX30 (V3.05 software) connected to a P70 (V3.07). A non-Raymarine chartplotter is connected providing navigation information over NMEA.

The AP works flawlessly in Auto mode and does a pretty good job in Wind mode (from an ST60 over ST through an ST-STng bridge). Where it fails completely is in Track mode. My old 3000+ wheel pilot used to handle this without problem 20 years ago.

The NMEA output shows I am sending ECRMB, ECRMC, ECAPB, GPVTG, GPGGA, GPGLL, and GPRMC sentences to the AP (and other units on the network). I don't have a Ray MFD, so can't grab diagnostics.

With the SPX30 here is my sequence:

Get the boat on track (XTE 0.00 or 0.01) and pointed on heading. AP heading output agrees with nav system heading within a degree or two. Display shows that the AP is receiving XTE, COG, SOG, BTW, DTW from NMEA (on rare occasions I have a hiccup here and I'l get the 'no nav data' warning, but that is pretty rare).

Change to track mode. The AP will change heading exactly 30 degrees. If the XTE sentence says -0.00 it will change to the right, if it says +0.00 it will change to the left - i.e. if the LH in Auto mode is 000 it will change to either LH 330 or LH 030. I can have zero XTE, but it changes course based on the sign of the XTE. This is with response from 1 to 3. If I set response higher than 3 (which is where I normally have it in Auto mode) the turns become larger.

Of course that gets it way off course so then it over corrects and turns 60 degrees the opposite direction. It takes about 15 seconds, but it pretty much always ends up at exactly 30 degrees the other side of the correct heading.

This continues forever, never settles out. The longest I've let it run is 30 minutes, it usually wears out my patience long before then.

Other than the response setting I haven't found any other adjustment I can make (such as limiting the LH deviation from the BTW to 5 or 10 degrees instead of 30).

Of course it doesn't do anything like in this in Auto or Vane, there it seems to run just fine. Any thoughts? Any additional data I can provide?

Thanks

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum DSanduril,

The description which you have provided is consistent with the design of a SPX autopilot when Track mode is initiated. Unlike Auto mode, which is designed to maintain a specific heading, Track Mode will attempt to maintain the vessel within a corridor extending either side of the course line. The width of this corridor will be based upon the autopilots Response Level setting. This feature supports nine settings. Should the value of this setting be configured to 1, then the autopilot will maintain a looser course, while a setting of 9 will permit the tightest course to be maintained. Having a properly functioning rudder reference transducer is also important to the operation of this feature. As the function of the autopilot is to keep the vessel within aforementioned corridor, it is normal for the track to appear as an elongated S.

[DSanduril]

The problem (from our perspective) is the severity of the turns used to maintain that corridor. If the SPX made turns of 5 degrees or thereabouts it could easily maintain an XTE of +/- 0.01 nm. That's what we currently do in Auto mode, manually adjusting course, usually only one or two degrees and we are able to maintain a very small XTE. It just takes a lot of attention.

If we switch to Track mode the turns become so severe that the corridor actually gets much wider, usually 0.05 or 0.06 sometimes up to 0.10 nm XTE because it takes so long to make the turn, get to the new heading, correct, etc...

We'll give it a try again at Response = 1 to see if that helps reduce the turn amount. If not, is there any other adjustment to reduce/limit the turn allowed in Track mode?

There is rudder reference transducer fitted and working properly, and as noted the AP performs quite well in all other modes.

[Chuck - Raymarine - Moderator]

DSanduril,

The farther that the vessel strays from course line, the greater the correction will be. As indicated within my prior response, higher Response Level settings will yield tightest course (i.e. lowest XTE) to be maintained and there by reducing the magnitude of the steering correction. It is accordingly recommended that you try increasing the Response Level to 9 to reduce the angle of the correct. Again, it is expected that the initial heading corrections will be fairly large, but will reduce in magnitude.