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108 GPSMAP 188/188C Sounder Owner’s Manual
APPENDIX > LORAN TD SYSTEM
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.
Change to Loran TD from the Units
tab on the Main Menu.
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 can be displayed as TDs,
and all navigation functions can 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 always references the
LORAN chain number and secondary stations currently selected in
the Setup TD field. If you enter a different LORAN chain number
or change the secondary stations or offsets in the Setup TD field,
the active waypoint information reflects those changes. Because
the GPSMAP 188/188C 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.