Originally Posted by Straightrazor41
I use a cetrek chartplotter
, it has a compass
page that gives heading so I thought they all did. .
I think you will probably find your chart plotter is showing COG not heading. It's important to understand the difference.
You can do this simple test to what is displayed. Look when you are at anchor
, or tied to a dock
. If its COG, as I expect, you will find the "compass" page on the chart plotter is all over the place and has nothing to do with the way the bow is pointing.
If it is heading data it will be steady and will reflect the direction the boat is pointing. (Just like an ordinary compass).
If you have an autopilot
leave this on as sometimes this will feed heading data into the chart plotter.
COG is very useful figure to have. It's one of the wonders of GPS
that we get accurate information on something that used to take considerable calculation and guesswork to estimate.
The difference between COG and heading tells is a lot about what currents and leeway is effecting the boat. If we loose the compass
we loose heading data and can no longer see the difference. Not understanding the difference between COG and heading data does the same thing