Plotter "Autoroute"

[MapisM]

@JR: 'salright, that's what I also learned to do, since I've got the Raymarine stuff on the DP.
My point was that with Furuno a/p you neither needed to fiddle with the plotter nor reset the XTE.
And as I understood, WL argued that even if can't go round the XTE reset with Raymarine a/p (because returning to track without doing that that would induce a silly hard over steering), you don't actually need to use also the plotter, because you can handle the XTE reset from the a/p control screen.
This is the bit I wasn't aware of, and which I don't know how to handle.

As an aside, the behaviour that you describe (rudder hunting when on track mode) sounds like you should swing your electronic compass.
IIRC, it's described in the manual as "compass calibration".

@WL: no worries, I take your word for it, and no big deal anyway - you just made me curious.
TBH, I can't remember what exactly is accessible from the ST6001, other than the usual a/p data.
On each helm station, aside from the larger screens, I have both that a/p head and the tridata, so I never use the a/p head for anything else than its main purpose...
Btw, did you refit your instruments yourself, or were they replaced by the previous owner? I'm pretty sure that they weren't available at the time your boat was built.

 

[jrudge]

As an aside, the behaviour that you describe (rudder hunting when on track mode) sounds like you should swing your electronic compass.
IIRC, it's described in the manual as "compass calibration".

The compass is pretty accurate on this one so I wont bugger about with it.

I just find heading hold simpler most of the time - just habit I suppose. The wandering is not bad, just a little worse than when doing a simple heading.

I dont think there is a way to reset the XTE from the control head. I have a new one ( 7001??? cant recall) with LED colour display etc and i am pretty certain it does not support anything like that.

 

[petem]

As an aside, the behaviour that you describe (rudder hunting when on track mode) sounds like you should swing your electronic compass.

P, would changing the A/P "Response Level" from "2" to "1" cure this symptom on Raymarine?

 

[Whitelighter]

I refitted them myself to replace the failing black ST50 autohelm kit.

They were the latest compatible kit to go with the RL80CRCs fitted by the previous owner

 

[MapisM]

P, would changing the A/P "Response Level" from "2" to "1" cure this symptom on Raymarine?

I don't think so. I'm not expert enough to tell for sure, mind.
But while response level can definitely affect... erm… the a/p response, I can't think of any reason why such effect should be different between auto and track.
In fact, afaik, the difference in the algorithms driving the auto and track modes has nothing to see with response level, because essentially the a/p always works as if on auto, with just one additional correction (if required) when on track.
This is far from being obvious, though. I'll try to explain what my understanding is on this matter:

1) when on Auto, the a/p checks the heading reported by its own fluxgate compass, compares it with the required heading which you selected, and constantly steers as required in order to minimize such difference. There's obviously much more than that in terms of possible parameters to fine tune, but in principle that's it - a relatively simple process.

2) when on Track, the logic becomes more tricky, because the a/p must consider (and let me stress again, afaik!) BOTH its own heading and the route-relevant data received from the plotter.
In fact, the a/p could never react fast enough if it should consider only the XTE, no matter how strict.
As a practical example, just think of a scenario where you are happily sticking to your plotted route, with a negligible XTE.
A wave hits the boat, changing her heading significantly, let's say by +10 degrees.
Now, if the a/p should move the rudders only whenever the plotter senses a meaningful XTE, it should wait for quite a while before making the -10 degree correction which obviously the wave-induced alteration requires, and which the sooner is done, the better.
Therefore, in order to react promptly enough, the a/p moves the rudders as soon as it senses a heading alteration from the fluxgate compass - pretty much as it does when on auto.
BUT, an alteration against what? In track mode, we don't feed any heading to the a/p, we just ask it to follow the plotted route.
The only unit which is aware of the required heading is the plotter, which in fact does not send to the a/p just the XTE, but also the BOD (Bearing from Origin to Destination).
This number is by definition a constant for each leg of your route, and could change only if and when you reset the XTE after a course alteration, or after reaching a WP and head for the next.
So, when you put the a/p on track, what happens if that it reads the BOD and the XTE from the plotter.
If the XTE is within a rather strict range which the a/p considers negligible (as it happens when you activate track right after resetting the XTE), all the a/p does is steer the boat till the heading received by its own compass matches the BOD.
And from that point onward, it keeps doing just that (as if it were on auto, and you would have selected the same heading as the BOD calculated by the plotter).
It does just that, UNLESS the XTE for any reason becomes not negligible anymore, in which case the a/p gives priority to XTE reduction, rather than stick to the BOD - to the point of steering hard over like there's no tomorrow with Raymarine, as opposed to much more smoothly with Furuno. But this is just a manufacturer's choice, irrelevant in this context.

Now, if you managed to follow my elucubrations so far without falling asleep, you will understand why I suggested to jrudge that his a/p might use a calibration.
In fact, the plotter calculates a theoretical BOD, based on the route waypoints.
Then the a/p takes this number and uses it as a reference for the correct boat heading, constantly comparing it with the number that it receives from the fluxgate.
A poorly calibrated fluxgate implies that the a/p actually follows a route which can be, albeit probably slightly, different from the ideal one.
As a result, the boat makes a sort of zigzag pattern, either to port or stbd of the ideal route depending on the fluxgate error, because the a/p keeps aiming for a "wrong" heading, till the XTE becomes meaningful and the a/p gives priority to it and takes care of bringing the boat back on the plotted route.
And all this quietly happens in the background, unknown to the helmsman. Wouldn't Christopher Columbus be impressed!?

All that said, I'm happy to be corrected on anything I said from whoever knows better!

 

[MapisM]

I refitted them myself to replace the failing black ST50 autohelm kit.
They were the latest compatible kit to go with the RL80CRCs fitted by the previous owner

Good choice.
Even if in several ways I still prefer the much older Furuno stuff in my old lady, which btw never missed a beat, I can see why the pathfinder generation of Raymarine instruments was so popular, back in those days.
In fact, I actually expanded a bit the OEM installation on the DP, without thinking for a minute to replace it with newer generation instruments.
I'd rather use man math for something else, like justifying 7 rather than 2 liters/Nm burned !

 

[jrudge]

Just to be clear following a route is not a disaster - i just think heading does it better!

I do find that it is very helpful to the auto helm to try and head it in the right direction before engaging a route as otherwise ( I assume for MAPISM reasons above) it does have to figure out what is going on by a bit of trial and error which does take some time.

I dont know how sophisticated the "computer" is on old Raymarine kit, but in essence is it trying to find the heading to steer that results in nil drift from track taking into account the real world behaviour of the boat which is influenced by wind, tide, waves and so on. It will I guess try a sensible heading ( as a human would) and then adjust to allow for what is happening and how fast ( which it should be able to calculate a opposed to the gut feel of a human).

I will re calibrate next year and see if it makes a difference, but the heading reported on the autohelm is always reassuringly accurate!

MAPISM - did you update your system and add in the joystick?

 

[Hurricane]

I don't think so. I'm not expert enough to tell for sure, mind.
But while response level can definitely affect... erm… the a/p response, I can't think of any reason why such effect should be different between auto and track.
In fact, afaik, the difference in the algorithms driving the auto and track modes has nothing to see with response level, because essentially the a/p always works as if on auto, with just one additional correction (if required) when on track.
This is far from being obvious, though. I'll try to explain what my understanding is on this matter:

1) when on Auto, the a/p checks the heading reported by its own fluxgate compass, compares it with the required heading which you selected, and constantly steers as required in order to minimize such difference. There's obviously much more than that in terms of possible parameters to fine tune, but in principle that's it - a relatively simple process.

2) when on Track, the logic becomes more tricky, because the a/p must consider (and let me stress again, afaik!) BOTH its own heading and the route-relevant data received from the plotter.
In fact, the a/p could never react fast enough if it should consider only the XTE, no matter how strict.
As a practical example, just think of a scenario where you are happily sticking to your plotted route, with a negligible XTE.
A wave hits the boat, changing her heading significantly, let's say by +10 degrees.
Now, if the a/p should move the rudders only whenever the plotter senses a meaningful XTE, it should wait for quite a while before making the -10 degree correction which obviously the wave-induced alteration requires, and which the sooner is done, the better.
Therefore, in order to react promptly enough, the a/p moves the rudders as soon as it senses a heading alteration from the fluxgate compass - pretty much as it does when on auto.
BUT, an alteration against what? In track mode, we don't feed any heading to the a/p, we just ask it to follow the plotted route.
The only unit which is aware of the required heading is the plotter, which in fact does not send to the a/p just the XTE, but also the BOD (Bearing from Origin to Destination).
This number is by definition a constant for each leg of your route, and could change only if and when you reset the XTE after a course alteration, or after reaching a WP and head for the next.
So, when you put the a/p on track, what happens if that it reads the BOD and the XTE from the plotter.
If the XTE is within a rather strict range which the a/p considers negligible (as it happens when you activate track right after resetting the XTE), all the a/p does is steer the boat till the heading received by its own compass matches the BOD.
And from that point onward, it keeps doing just that (as if it were on auto, and you would have selected the same heading as the BOD calculated by the plotter).
It does just that, UNLESS the XTE for any reason becomes not negligible anymore, in which case the a/p gives priority to XTE reduction, rather than stick to the BOD - to the point of steering hard over like there's no tomorrow with Raymarine, as opposed to much more smoothly with Furuno. But this is just a manufacturer's choice, irrelevant in this context.

Now, if you managed to follow my elucubrations so far without falling asleep, you will understand why I suggested to jrudge that his a/p might use a calibration.
In fact, the plotter calculates a theoretical BOD, based on the route waypoints.
Then the a/p takes this number and uses it as a reference for the correct boat heading, constantly comparing it with the number that it receives from the fluxgate.
A poorly calibrated fluxgate implies that the a/p actually follows a route which can be, albeit probably slightly, different from the ideal one.
As a result, the boat makes a sort of zigzag pattern, either to port or stbd of the ideal route depending on the fluxgate error, because the a/p keeps aiming for a "wrong" heading, till the XTE becomes meaningful and the a/p gives priority to it and takes care of bringing the boat back on the plotted route.
And all this quietly happens in the background, unknown to the helmsman. Wouldn't Christopher Columbus be impressed!?

All that said, I'm happy to be corrected on anything I said from whoever knows better!

I read all this stuff years ago and as I get older, I forget things - especially stuff that I don't use much so this post might be all wrong.
I'm not sure about your above logic - I've never really thought about it.

But I challenge your point about using the Auto rather than a Route.
We used to use Routes in the early days but these days, we don't bother.
BUT without a doubt, we use Go To Cursor a lot.
Only using specifically Auto during pilotage (into and around marinas etc)
But Go To cursor to all intent and purposes forms the same argument - Go To Watpoint is really just the current leg of a Route.
And Go To Cursor is SO useful, I believe it should be the MOST important thing that anyone is taught on a navigation course - way more important that any paper nav.
And how many newbies actually know about Go To Cursor??

I use it differently to the way that has been explained on this thread.
My plotters (Raymarine GPM's actually) show the course to the next waypoint.
Once the Auto Pilot is set to navigate to a waypoint (Go To Cursor) and if we alter the course for any reason (encounter ship - play with dolphins etc) we disengage the Auto Pilot from Track to either Auto or Standby mode.
When we want to go "back on track" we use a Plotter to "reset its XTE and then re-engage the Autopilot. Our system allows us to do all this from the Plotter's control interface without using the ST6000 control head.
This process of changing the "track to next way point" avoids the sudden turn back to the original track.

I've never used the XTE option inside the ST6000 head.

AFAIK - Response adjusts the amount of time that the rudders are being used.
Sailing boats don't have the power available that we have so it suits them to let the auto pilot make fewer adjustments to keep the boat on course.
Our system defaults to a Response level of 2 - I usually change it whilst under way to a Response level of 3 (by pressing +1 and -1 together at the same time).
If you look at the boats wake, you can easily see a difference in the various Response levels when you adjust them.

There is also a setting for Rudder Gain which I believe adjusts the amount of rudder that is required for a particular adjustment.

As I say, it has been a long time since I read the manuals but this Go To logic run from the plotter works for me.

 

[MapisM]

MAPISM - did you update your system and add in the joystick?

I feared this question, 'cause not yet is the short answer, I'm afraid.

Trouble is, when we reached CF after having "missed" last summer, our agenda was overwhelmed with all sort of trivial commitments...
...and onboard DIY activities quickly fell down in the ranking of priorities!

I won't forget to post about that job whenever I will tackle it, anyway.
Don't hold your breath, though!