Appendix B: Loran Td - Garmin GPSMAP 178 Owner's Manual

Appendix B
Loran TD
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 field,
highlight 'Loran TD' and press ENTER to
select Loran TD.
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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 posi-
tion as a TD or enter waypoints as TDs. The accuracy to be expected from this conversion is approxi-
mately 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 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. You must have the
correct chain number as well as the secondary station identifiers to use this option correctly. These values
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 always references
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 reflects 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.