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On the Units Tab of
the Main Menu, press
MENU, then highlight
‘Loran TD On’ and
press ENTER to select
Loran TD.
Or, highlight the Position
Format fi eld, highlight
‘Loran TD’ and press
ENTER to select Loran TD.
102
Appendix D
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 Confl uence 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 collec-
tion of LORAN fi xes for favorite fi shing 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 thirty 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 func-
tions 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 fi eld before storing the waypoint. You must
have the correct chain number as well as the secondary station identifi ers to use this option correctly.
These values will vary per coordinate set or geographical location. Failure to enter correct information
could result in inaccuracies for the desired destination. 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 fi eld. If you enter a different LORAN chain number, change the secondary stations or offsets in the
Setup TD fi eld, the active waypoint information will refl ect 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.
188188C238 Manual Part 2.indd 102 6/30/2003, 3:32:46 PM