Rich... My old waas enabled magelan seems to do better when it comes to accuracy. At the same time I would hope that the units would compensate for those inaccuracies because otherwise the max speed would be all over the place. Not sure what the samplerate is - assuming the unit samples a few times a second - having those samples taken up to 40 feet apart would result in high speed readings while standing still.

What type of Garmin Mapsource Software are you using? Anything available for marine use? Just some topographic map? Thanks

Patrick