Using Loran TD with a Garmin Marine Device

Garmin® has added the Loran TD format to all current GPS devices; this allows consumers who have used Loran in the past to enter old Loran TD numbers into their new Garmin GPS devices. The GPS does not receive a Loran signal. It only converts the Loran TD that is entered and converts it to Lat/Lon for display or navigation.

The device will need five pieces of information to create a Loran TD waypoint and work properly. The user will need to know the main chain station (GRI_xxxx), the call sign of the two substations used in their area (Typically W, X, Y, Z), and the time offsets for each station (usually a low number, and can be positive or negative). If any information is incorrect, the waypoint will not be in the correct location. For more information on Loran TDs, refer to the Loran TD Position Handbook.

After setting up the chartplotter for Loran TDs, enter the Loran waypoints, then switch the GPS back to a Lat/Lon position format. The device will automatically convert the waypoints from Loran TD since the GPS device makes the conversion based on a static model, only expect accuracy within about 100 yards. An error occurs if an incorrect primary or secondary station entry input or the two secondary stations’ order is incorrect. We recommend you mark these waypoints upon arrival using the GPS signals received for the most accurate position because of this error.

The LORAN system was taken offline in 2012 by the US government. If information about stations, chains, and offsets values is necessary, contact the USCG. Unfortunately, if the USCG cannot supply the required information (Chain numbers and offset values), the Garmin device will not accurately calculate.   

For more information about changing settings or manually creating waypoints, refer to the Owner’s Manual of the device.