How to Use a Marine GPS
A marine GPS, or Global Positioning System receiver, can tell where where you are; the bearing, distance and time to get to the destination you select; the expected time of arrival based on the current course and speed; and exactly where the boat has been, so that you can backtrack to rescue anyone who fell overboard. Even the least expensive marine GPS units provide an electronic compass that allows a true course--shown on marine charts--to be followed.
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Instructions
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Turn the GPS on by pressing the power button, usually the button with a picture of a circle with its top interrupted by a vertical line. The first display is the current location of the GPS, in terms of latitude and longitude.
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Press the "Menu" button. To go to a destination, scroll to "Waypoints" and touch "Enter." Select a pre-existing destination or press "New." To enter a new waypoint, enter the numerical component of the destination's latitude and select "N" for locations in the Northern Hemisphere, or "S" for locations in the Southern Hemisphere. Enter the destination's longitude and select "E" for locations in the Eastern Hemisphere or "W" for the Western Hemisphere. Press "Enter" and the GPS will shift to the navigation screen or position window.
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The navigation screen displays distance, or DST, and bearing, or BRG, from the boat's present location to the destination, as well as time required to reach the destination--the time to go or TTG, and the estimated time of arrival or ETA. The bearing is the optimum course to be steered to arrive at the destination at the ETA. The navigation screen also displays, the vessel's current position, usually in the upper left corner.
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Press the "Menu" button again and scroll to "Track," and the vessel's track--what turns it's made, and where--will be displayed. Minor course corrections of less than 15 meters are recorded. To see small changes in course, use the arrow keys to move the screen to a specific location on the track, and touch "Zoom."
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If someone falls overboard, touch the "Man Overboard" key, or MOB, immediately. The MOB key creates a special waypoint that is visible both in the navigation screen and on the "Track" screen, allowing the person at the helm to return to within 15 meters of the location where the man overboard was reported.
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Tips & Warnings
Like any other electronic device, GPS receiver models vary from one to another. "Menu" might be different, or it might even be represented by the presence of a virtual key on the screen instead of a button. The only common feature is the Man Overboard key. Reading the instruction manual for your GPS will increase its utility.
Never use the MOB key to mark locations where you've seen something that's merely "of interest." Instead, write down the latitude and longitude displayed on the navigation screen.
