Raymarine Chart Plotter - Strange Track / Heading Angle

[FraidNot]

I seem to have a heading angle offset sometimes with my Raymarine C70 chartplotter.
For example:
Boat: Hdg Nth directly at a bouy. No tide - so hdg and CMG are the same.
Plotter: has the line boat-bouy offset some 15 degrees from straight-ahead. Boat icon does track to bouy.

I have changed from Nth Up, to CUP to HUP and it doesn't seem to go away. This only seems to happen once every few weeks. Hmm.

As a variation to this - on plotter I have had a few occasions where the boat icon has shown heading off perhaps 45 deg from actual - but the boat icon does crab along the correct CMG line. Weird!! Seems to fix itself eventually. Only happened a few times. Messes with your visualisation of terrain!

Ideas?
Plotter and autopilot are both in MAG with correct local variation set.

[scotte]

What inputs are hooked up and what feeds them? Do you have both COG (yellow) and HDG (red) vector lines (from memory, I think I have those right)?

I had a somewhat similar problem, turned out to be a bug in the C70 software combined with my particular configuration (a Brookhouse NMEA MUX which echoed bogus VHW sentences generated by the C70 back, which the C70 would then assume were valid). I had another problem when the C70 would get confused when it received the same sentences both on it's local SeaTalk bus, as well as via NMEA (the MUX has built-in SeaTalk conversion). The solution to that was some filtering rules on the MUX.

Here's the response from Raymarine support, if it helps:

VHW Is a NMEA sentence generated by both C & E-Series displays when mechanical water speed (via a DSM module or instrument received via Seatalk) is connected to the displays.

This sentence is given a false heading and transmitted over NMEA if no other heading is available via either NMEA or Seatalk.

If the NMEA receiving units, such as some position polling VHF radios do not buffer this sentence; it will be looped back into the plotter displaying both an inaccurate heading and also a skewed vessel indicator on the display.

This can be solved by turning OFF the VHW sentence in the C/E-Series NMEA Output portion of the menus.

In my case, there was a valid heading available, but the C70 would still sporadically seem to choose this invalid VHW sentence instead.

Not really sure if this is your problem, but it's similar and maybe this will help with problem determination. Easy to turn off VHW sentence output to try it!

[Bill S]

Do you have an autopilot with a fluxgagte compass connected to the system? If so, I think that the heading information is picked up from the fluxgate and the calibration or deviation of the fluxgate may be off. I wish that Raymarine would explain in its documentation where various data was coming from.

Bill

[David M]

I have had fluxgates stick. One time I had to replace it and the other time getting underway and having the boat pitch and swing allowed it to unstick.

[scotte]

Originally Posted by scotte

COG (yellow) and HDG (red) vector lines (from memory, I think I have those right)?

I verified it's COG (green) and HDG (red). Sorry about that.