The GPS' are a cool toy but dont bet on the maps to be accurate to within 1000 feet. Or a depth of +/- 5-10 ft. I have seen mine with the "more accurate" maps show me standing in the ocean or on dry land when I was not. I use it as an amusement not as a protection from hazards. Use the chart and the GPS as a reference and then stay well clear of real hazards.