How to Convert Loran to GPS Numbers
By Will Charpentier
LORAN was an electronic navigation system used in the United States from 1958 to 2010. It compared the signal strength of the radio signals from any two LORAN transmitters to identify the location of a shipboard receiver on an electronic grid, accurate to within 1 mile. The Global Positioning System (GPS) is an artificial constellation of satellites, using computer technology to localize a vessel based on the relative distance from three or more satellites, and accurate to 15 feet or less. Some computer programs convert LORAN to GPS, but their calculations aren't quite as accurate as manual conversion.
Copy the LORAN readings on paper with a pencil. LORAN-C receivers built after 1980 gave their "time-distance" (TD) readings in latitude and longitude, without the north/south or east/west indicators, so the "degrees," "minutes" and "seconds" of the position will be the same for the GPS as they are in the LORAN reading.
Add the north/south and east/west indicators by penciling in an "N" for North latitudes, "S" for south latitudes, "W" for west latitudes and "E" for east latitudes after the readings for latitude and longitude. If a location is north of the equator, it's in north latitudes, indicated by the letter "N" following the "degrees/minutes/seconds" reading. Locations south of the equator are in south latitudes and indicated by the letter "S" following the "degrees/minutes/seconds" reading. Locations west of the Greenwich Meridian and east of the International Date Line are west, and indicated by the letter "W" following the "degrees/minutes/seconds" reading. Longitudes east of the Greenwich Meridian and west of the International Date line are indicated by the letter "E" following the "degrees/minutes/seconds" reading. Almost all LORAN-C readings are in North latitude and West longitude, because the LORAN system was based in the United States and the Eastern Soviet Union. The sole exception to West longitudes was in the waters of the Bering Straits, west of the International Date Line.
The indicators are essential in converting the LORAN readings to GPS waypoints: a position that's 90 degrees west longitude and 29 degrees 57 minutes north latitude, for instance, is in New Orleans, LA. A position that's 90 degrees east longitude and 29 degrees 57 minutes south latitude is in the middle of the Indian Ocean, halfway between the west coast of Australia and the east coast of Africa. Without the indicators, the GPS might send you to the Indian Ocean instead of the French Quarter.
Transfer the latitude and longitude, with north/south and east/west indicators, from your notes on the readings from the LORAN unit to the GPS receiver, by entering the "Navigation" screen and using the number keypad to enter the numeric part of the latitude, then using the arrow keys to select "North" or "South" latitude. When the GPS prompts you for the longitude, enter the longitude using the number keypad to enter the numeric part of the longitude and the arrow keys to select "East" or "West" longitude.
For example, touch "Navigation," then use the keypad to enter "29 57 00" in the first set of blanks--flashing, before you make an entry--and touch "Enter." When the second set of blanks begins to flash, enter "90 00 00" and touch "Enter." As soon as you touch "Enter," you will be returned to the navigation screen and the waypoint will appear, along with the distance, travel time and compass bearing to the waypoint.
- Before the introduction of the GPS, navigation was a hodgepodge of national or regional systems. LORAN C wasn't functional in European waters, the Southern Ocean, or the Western Pacific east of the International Date Line--meaning that all valid LORAN C readings are West latitude and North longitude.
Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history.