How to Use a GPS on a Boat


A marine GPS provides not only your own boat's location but shows you the course to steer to reach that destination, both graphically and as a heading or course to the destination once you have the coordinates of your destination in hand. Some GPS units give only this basic information; others, called chart plotters, may render a navigational chart on the display screen to show your boat's approximate location relative to the maritime environment. Whichever type of GPS you have, visually confirm the information it presents and operate for the safety of the vessel.

  • Turn on the GPS. The default screen on most GPS units is the navigation screen where you can enter the latitude and longitude of your destination. Use the GPS manual's directions for that operation. As you enter the latitude, the GPS will offer an option: "N" or "S". Choose "N" for latitudes north of the equator or "S" for latitudes south of the equator, depending on your destination's location.

  • Enter the longitude for the destination. As with the "N" or "S" entry for the latitude, the GPS will query, "E" for longitudes east of Greenwich, UK, and "W" for longitudes west of Greenwich. Once the latitude and longitude are properly entered, verify both once more on the GPS before departure.

  • Move your vessel away from its dock or mooring and, while observing the navigation rules and restrictive buoyage present, if any, turn your vessel toward the course displayed on the GPS. Press the "Navigate" or "Go To" key as you leave the harbor or marina. A "course line" representing a straight-line course to the destination will appear, originating at your current position and terminating at the destination. The GPS will also display the course-to-destination, the course you should steer to reach your destination.

  • Keep your vessel to the course, while maintaining a lookout for any obstructions, such as other boats or land masses, navigating around them in a generally prudential manner. The course line still represents a straight line between the destination and the point where you instructed the GPS to go to the destination. The graphic display on the GPS will also show you how far you are from that line. As long as you steer the course-to-destination indicated by the GPS, you will head directly for your destination.

  • Notice that when you reach your destination, your GPS unit may have a "reverse course" option. Follow the instructions for your particular GPS to initiate this feature, which will display the return course to your starting point.

Tips & Warnings

  • The prudent mariner will trust no single navigational source, and should take relative bearings between his vessel and any visible landmark to ensure the vessel is progressing safely along its correct course.
  • There is no substitute for visual confirmation of the information that an aid to navigation, such as a GPS, provides.

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