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Reference
Main Menu: Units Tab- Loran TD
Loran TD System
LORAN C is a radio navigation aid operated and maintained in the United States by the United States
Coast Guard. The name LORAN is an acronym for “LOng RAnge Navigation”. The LORAN system covers
the entire United States and the U.S. Coastal Confluence Zone. From the perspective of a mariner, the
system is used for ocean and coastal navigation. It can be used as a supplemental system for harbor and
harbor approach navigation, and it is used for inland navigation by recreational vehicles.
LORAN TD Feature
The LORAN TD (Time Delay) feature eases the transition from using LORAN to using GPS. The
GPSMAP unit automatically converts GPS coordinates to LORAN TDs for those who have a collection of
LORAN fixes for favorite fishing spots and other waypoints recorded as TDs. You can display your position
as a TD or enter waypoints as TDs. The accuracy to be expected from this conversion is approximately 30
meters. When the unit is placed in the LORAN TD format mode, it simulates the operation of a LORAN
receiver. Position coordinates may be displayed as TDs, and all navigation functions may be used as if the
unit was actually receiving LORAN signals.
Using the LORAN TD Format
When creating new waypoints using LORAN TD coordinates, you must set the correct LORAN chain
number and secondary stations in the Setup TD field before storing the waypoint. After the waypoint is
stored in unit memory, it will always reference the LORAN chain number and secondary stations currently
selected in the Setup TD field. If you enter a different LORAN chain number, change the secondary stations
or offsets in the Setup TD field, the active waypoint information will reflect those changes. Since the
GPSMAP unit does not rely on the LORAN signal for navigation, it can reference a different GRI chain
and/or secondary stations and still navigate to the location stored in memory.
The LORAN Position Format field is located under the Units tab in the Main Menu. The ‘LORAN
TD Setup’ window contains the fields to select the Loran GRI-Chain Number, Primary and Secondary
Stations, and TD Offsets.
