Prudent Mariners Need A GPS Backup

Since Nathaniel Bowditch first put pen to paper in 1799, those practicing the art of maritime navigation have had as a first rule: “Prudent mariners use all means available to determine their position.” Today, the modern version of Bowditch’s “The American Practical Navigator,” published by the National Geospatial Intelligence Agency (NGA), more expansively says:

Use all available fix information. With the advent of accurate satellite navigational systems, it is especially tempting to disregard this maxim. However, the experienced navigator never feels comfortable relying solely on one particular system. Supplement the satellite positions with positions from Loran, celestial fixes, radar lines of position, soundings, or visual observations. Evaluate the accuracy of the various fix methods against the satellite position.