Tried cmapecs again, didn't work like it did yesterday.
Then I moved the GPS-puck about 3 meters. After 20 seconds I had COG and SOG and own vessel position indicator. Waited some minutes, switched cmapecs off and restarted. No own ship indicator. Moved the GPS-puck and got COG, SOG and position indicator.
Restarted the computer, started cmapecs on and got all the bad indications. Moved the GPS-puck and after 20 seconds I got COG, SOG and position indicator. Moved the GPS-puck back to the original position, everything still ok.
If you leave the GPS-puck in the same position for some minutes the COG indicator starts flashing on and of, and so does the position indicator. Also the sign "no position" starts flashing.
Seems cmapecs needs at least 2 gps
positions to start working properly. I wonder if it makes use of the speed and course data provided by the GPS-puck or if it calculates these based on the gps positions.