Losing Our Waypoints

[bhcva]

Search reveals no clues....so...is anyone else 'losing' the next waypoint on routes that are near due north? We are having the problem with the stable version and the 6.2.8 beta. The waypoint on my radar screen will erratically jump to the west about 100 degrees or so...and the ownship will display rotated apparently the same amount in the opposite direction. Steering away from the near-north waypoint will help stabilize the situation.

The config is raymarine ethernet data into/out of the laptop via a ray converter to nmea...output via the autopilot interface.

Other than that OpenCPN is working wonderfully on our trip to Maine from the Chesapeake. Great job by the team.

Bruce

[Littlechay]

As the waypoint is displayed on the Raymarine display it presumably has been uploaded from OpenCPN to the Raymarine system.

Disconnect OpenCPN and see what happens.

What versions are you using? of everything?

[nilespf]

Is it a raymarine pilot and what is the Chart Plotter?

[bhcva]

little...yes, the waypoints are coming to the sl70 radar screen via the nema to seatalk i/f from opencpn...disconnecting opencpn would accomplish nothing except to lose the wps. the gps info is coming to opencpn from the raymarine gps, thru the ray 620 chartplotter and the nmea-seatalk i/f (by raymarine). there is no autopilot...opencpn outputs via the pilot com port.

Possibly the error is being introduced by the radar or by the i/f box? what confuses me is that the ownship is displayed by opencpn with the incorrect azimuth when the problem occurs.

the chartplotter cannot be taken out of the mix as it is the interface for the gps.

apparently no one else is having this problem so i will try other approaches...if there are any that will get all my data (includimg opencpn output) displayed on the radar screen.

[nilespf]

I'm sure I do not understand how your system is setup. If you have not already solved the problem, let us know how the system is setup. I need to know what mode your operating the 620 in, what model GPS and how is the system interconnected? It seems as if there may be some trashing of data going on. What do you mean by "there is no autopilot...opencpn outputs via the pilot com port."

Phil

[Littlechay]

A better description of your setup or a diagram would help us here.

Sounds to me like it could be a heading data issue. What speed is this happening at? If your heading data is coming from the GPS and you are slow your COG could be all over the place giving the symptoms that you describe.

What provides your heading data? Compass or GPS giving COG?

Chris

[bhcva]

Little...no relation to cog...sailboat speed.

The config is simple....Ray gps, 620+ plotter, sl70 radar all on seatalk....it's old, but works fine. I added a seatalk - nmea convertert/translator which feeds the pc with opencpn and receives the waypoint data from opencpn which is then displayed on the radar screen...course and distance (perhaps more) ....the radar displays the waypoint exactly as it would had it been sent by the plotter. All works well except when the course is around due north.

The plotter is not managing the routes/waypoints....it is interfacing with the gps and putting appropriate data on the net that opencpn uses. I would turn it off except that it needs to interface to the ray gps and, if it's not on, the other instrumnents aren't displayed...it may be powering the seatalk net?

After reading one of the other threads here, I believe the problem has to do with conversion from opencpn's true headings to the mag headings the radar uses. I do not know who does that translation....probably the radar...it's not rocket science to deal with the north problem??

What does confuse my is why does opencpn display the ownship heading shifted to the east by the same amount the waypoint shifts to the west???
The distance to the wp is never wrong.

Bruce

[Littlechay]

Bruce.. I think this has a lot to do with COG.

What mode is your radar in; Head up, Course Up, North UP? What is the source of the heading information to the Radar? Do you have a Raymarine fluxgate compass in your system or is the heading data only coming from the GPS COG?

The reason your are getting opposite shifts is that the radar is aligned to the course of the boat. The course data is shifting more east therefore the relative bearing to the waypoint changes and it is shown on the radar as being further west. i.e. the radar thinks the boats heading has changed.

The problem is the COG info that OpenCPN has is changing, causing it to output an incorrect relative bearing to the WP.

If you can tell us what mode the radar is in that will help with understanding the problem.

I doubt very much that it has anything to do with magnetic or true. The heading info is labled on NMEA and seatalk and the instruments will use whatever is appropriate to their setting.

[bhcva]

Little..remember, this never happens unless the boat is on a heading close to due north.

The radar is in a course up mode. I'd have to check the nmea sentences that opencpn is sending...if opencpn is sending cog, then it's probably coming from both open and the plotter... i believe that it is coming from the plotter for sure.

You state that the course is shifting more to the east....just to make it clear, the real course to waypoint is not shifting, it's somewhere near 000. When this 'jump' of the waypoint about 100 degrees to the west, the open icon is shown pointing that same (?) amount to the east...sporadically!....this jumping comes and goes while on this course. As i said earlier, the farther i steer away from the course the less 'jumping' there is.

Bruce

[bhcva]

Little...the plotter is providing cog, sog to the system. So the problem is ocurring in the plotter which explains why the ownship shows incorrectly in opencpn. In 12 years prior to introducing opencpn I've never seen this problem so there is something in the interface that's causing the problem and I'll bet that it's the mag vs true 'conversion' in the plotter.

Bruce

[Littlechay]

Bruce, yep I thought this might be the case, but didn't have enough info.

I wouldn't be so sure about the mag to true conversion, that could very well be a red herring.

You imply up the page that the radar is using mag mode. Apparently you don't have a fluxgate compass; so in fact you have no magnetic input into your sytem at all.

My suggestion as a next step is to make sure your entire system is displaying all courses and bearings in true. That way there are no conversions in the system. That should eliminate the mag / true conversion issue, or confirm it.

Have you upgraded the firmware in the plotter? I am not familiar with that model but you can usually upgrade by downloading a fix to a card and booting the plotter with the new card installed in the chart slot.

Is the GPS built into the plotter with an external antenna; or is the GPS one of the newer Raystar units which has all the brains inside the mushroom? The antenna will have a coaxial cable output from the mushroom, the Raystar will have a seatalk cable output from the mushroom, and it will also have a LED on it the blinks to tell you various diagnostic information.

[nilespf]

bhcva,
Is this correct:
The converter connects to CPN via the RS232 port only. The converter seatalk out goes to the SL70. The converters other seatalk out goes to the 620. The GPS goes to the 620 and the SL70 has no NMEA connectors utililzed.

It is my understanding the following sentences are used by Raymarine Radar displays and in this order:
1. Bearing from origin to destination, i.e. intended course.
2. Locked heading from an Autopilot.
3. Bearing to waypoint.
4. Instantaneous heading.

Try changing from course up mode to N up to see if the processing of the above is changed. What is the speed of the vessel when this occurs?

Phil

[bhcva]

yes...sorry...no fluxgate...

the 620 plotter hasn't been supported in years...the gps is circa 2001 w/ a cable direct to the plotter....believe it is rather dumb?

have thought about going all 'true'...will gtry it when i get a chance...in the middle of a trip.

Bruce

[bhcva]

niles...you're essentially correct keeping in mind that there is only one seatalk connection per device...no direct connect to sl70. no nmea i/i to sl70.

don't know about the priority of sl70 processing...i'll change to n up when the problem occurs to see if it makes a difference.

bruce