[SeaSparks]

There is no practical way of shielding against EMI on your boat. To be honest, I have only seen one device actually effect a compass, and that was a tach.

Marine electronics are built fairly well, and usually dont effect a compass at all. Have you noticed a change with the GPS installed vs removed?? If not, don't sweat it

Small boat compass are terribly inaccurate to start with.

 

[SeaSparks]

Yeah when I turn on gps it will turn a little over 90 degrees. The garmin unit instructions is telling me to mount it 39 3/8 in away from the compass. My console is not that big...LOL

Wow!!! I never have seen one that bad!! Unfortunately the only way to really block EMF is going to have more of a adverse affect on the compass.