Help? I got a HB 581i for Christmas and I have installed it on the bow of my boat. The boat icon (on the GPS screens) wanders wildly. The boat is sitting still, on the trailer, and the boat icon moves around as much as several hundred feet in every direction. The speed readout reads anywhere from 0.3 to 1.4 mph. I did send HB an email about it, but I'm afraid they may be off for the Holidays. Anyone know anything about this?