So which is our primary? We have a Garmin GPSMap at the helm and our Nobeltec Passport charts with a small USB gps receiver plug-in. We can plug the laptop into the original GPS that came with the boat, but the newer USB GPS receiver is WAAS capable and more accurate.

Beyond those two, we also have the original GPS on the boat which serves as a backup to the laptop GPS USB receiver. And also the original Magellan GPS that we used from Annapolis to Charlotte Harbor FL ... we actually got it for free by test driving a Cadillac. Didn't want the car, but the GPS was very functional and still serves as our back up to our back up.

I also have an iphone, but we've never tried using it for navigation or as a gps.

Cheers! J