How to Read a Marine GPS
Depending on the make and model of GPS receiver, you' may find yourself swamped with navigational information. In addition to your current latitude and longitude, screens may include a digital compass, a display that showing your boat's position--left or right of the center line--telling you how far you are off your optimum course (this is called the cross-track, or "XTRAK" feature). You'll even have an exact graphic showing exactly how you got where you are, in case you need to backtrack to look for someone or something that fell over the side.
Other People Are Reading
Instructions
-
-
1
Turn the GPS receiver on. The first screen you see, after the unit acquires satellites, will tell you your current latitude and longitude. Latitude has the letter "N" for north latitude, or "S" for south latitude in front of the numbers. Longitude has the letter "E" for east latitudes and the letter "W" for west latitudes in front of the numbers. Your current latitude and longitude are displayed on all screens, will change as you move and your position changes, and can be used to plot your current position on your paper chart.
-
2
Press the "NAV" button to change screens; the order that screens appear depends on the make and model of GPS receiver. All receivers have a digital compass screen, a cross-track, or "XTRAK" feature showing how far you are from the optimum course and a graphic of the route you've traveled so far. The digital compass is read exactly like you read any compass; if it says your heading is 036 degrees, then your heading is 036 degrees.
-
-
3
Use the XTRAK (cross-track) screen to tell how far you are left or right of the optimum course to your destination. That's what XTRAK does: it shows you the line that's the shortest course, and it shows you how far you've wandered away from that course because of winds or currents. If you're right of the center line of the track, steer to the left to compensate.
-
4
Look at the screen and find the numbers next to the letters "DTD" (Distance to Destination) and "TTG" (Time to Go). These are the distance and time to the next waypoint (if you have entered a destination) on your voyage that you've programmed into the GPS, in a straightforward digital format. The DTD and TTG will decrease as you near your next waypoint.
-
5
Move to the "TRK" or "TRACK" display and you can see where you've been, including any movements away from the course to your destination. This is useful because it gives you an accurate representation of the track you've followed to reach your current position: if you have a MOB (man overboard) situation, you can return to any point on your track to search for your missing crew member.
-
1
Tips & Warnings
The latitude and longitude on your GPS are displayed in "partial decimal degrees" by default, meaning that the display will show degrees and of latitude or longitude; minutes and seconds are displayed as a decimal portion of a degree: N 29.034 isn't "North 29 degrees, 3 minutes and 4 seconds"; it's North 29 point 034 degrees. You can switch to a standard Degrees Minutes Seconds display using the "Setup" function on all receivers.
GPS is an electronic marvel, but have paper charts on your boat and use them for planning and to keep a running plot of your position every half- or quarter-hour, in case the GPS fails.
