I have a somewhat lengthy and technical GPS question. I have a Garmin handheld 76S but I suspect this question may be generic. I charter frequently and use the unit in the cockpit. It is usually found propped up near the binnacle. One night I was using the unit to follow my heading only to eventually figure out it was about 30 degrees off compared to the binnacle and my handheld.
As I read through the manual it noted that the unit is set up from the factory to use an electronic compass to establish heading at speeds <10 mph and to use the GPS receiver at speeds > 10 mph. Clearly I am always going < 10 mph. I can change the default setting so it will use the GPS receiver for navigation instead of the electronic compass at speeds down to 0 mph.
So here are my questions:
1. I assume the GPS was way off that night because I had it propped up (the instructions say the electronic compass likes to be flat) and it was near the binnacle compass and a radio. Does that sound right? Is an electronic compass subject to the same interference problems as a magnetic one? I really do not know what is meant by an electronic compass.
2. Is there any reason not to change the settings so that the unit is always using the GPS receiver to navigate, i.e., I can change the default down to 0 mph? I know that a GPS only navigates "correctly" when one is moving but of course in a sailboat when not moving I am generally anchored and using my handheld regular compass anyway.