Chartplotter heading vectors

[Painkiller]

I have a Raymarine C120 chartplotter, GPS, and radar system in my 2005 420. As you can see the picture showing the heading vector (red) and COG vector (green) are different. The boat in the chartplotter is pointed along the heading vector. However, the boat is actually heading in the COG vector direction. Is this deviation between the two vectors typical or is something wrong? I believe something is wrong for a number of reasons such as autocorrect on my autopilot takes me off actual course. Does anyone have an idea on what I need to do to correct such as recalibrate the system, call a professional, etc? Thanks.
Tim

 

[Jaybeaux]

Variations in COG and Heading are "normal" and can be attributed to external forces such as wind or current. From your picture, I would assume that the wind that day was coming from your Starboard side.

Have you ever seen a video of an airplane landing in a strong cross-wind? Pilots call it crabbing...

Jaybeaux

 

[Woody]

It's not always the same is it? I mean, some times the boat symbol/heading vector could be pointed to port, or anywhere between.

The projected COG comes from your GPS(satellites). It knows this because it knows where you are now and where you were a bit before. It knows that's the direction your moving at that point in time but I does not know which way your boat is pointing, only which way it's moving.

Your fluxgate compass properly orientated/installed knows which way you boat bow is pointed. It's the fluxgate that feeds the autopilot so correct steering inputs are made to keep you on course, like when you go to a waypoint.

Sometimes the COG and heading should be the same or pretty close, like no wind, waves, swells, tides.

It is possible though that your fluxgate needs to be calibrated/orientated, there's probably a procedure for that in the manual. I think it involve driving slowly around in big circles.

 

[Creekwood]

You can also align the compass to the COG. Firat recalibrate it and then align it to COG. Look it up in the manual. I can’t recall the steps.

 

[juggernaut1]

Not sure what ap you have, but see if its in the below manual link. If it's covered by the manual, calibration is at page 28.

http://www.svsarah.com/Sarah/Manual...02, ST8001, ST8002 controllers 81273-2-EN.pdf

 

[Painkiller]

Thanks everyone. I will try to calibrate this weekend if weather permits. It just seems like the heading vector is always 20 degrees off no matter what the conditions are.