LORAN-C was the first method of electronic navigation that was both widely available and affordable for small boat owners. The use of LORAN-C revolutionized saltwater fishing in many ways. Prior to LORAN-C, anglers used a chart, ruler and compass to navigate. Finding the way out and home again was time consuming, distracting and sometimes dangerous.
When most people mention LORAN, they refer to LORAN C which is a refinement of earlier LORAN systems. LORAN C is widely misunderstood and does have it's peculiarities. The basic concept uses a radio receiver to determine a vessel's position by determining the time delays or TD's of an array (typically 2) of LORAN stations.
LORAN-C receivers obtained TD's for W, X, Y and Z stations in the mid-Atlantic region. A pair of numbers displayed on a LORAN equates to a certain geographic position. The exact value can be affected by several factors but the repeatability of a fix obtained by LORAN was excellent by standards of the time period. Charts were overlaid with lines of position for W, X, Y and Z stations. The predicted lines were very accurate over open water but cannot be predicted over land.
During the 1990's there was a big scare related to possible shutdown of the LORAN C system. As a result, most mariners scrambled to buy GPS receivers. Later the government decided to extend the life of LORAN C. The popularity of LORAN equipment never regained it's momentum and eventually the U.S. LORAN C system was shut down.
LORAN-C has several characteristics that make less attractive than the new GPS equipment. LORAN-C needs a bulky antenna, making portable units impractical. Other disadvantages include the need for specialized charts, area specific coverage, and the tendency of receivers to shut down during electrical storms.
Many old fishermen have a crumpled old book filled with pairs of LORAN TD's for fishing spots, wrecks, buoys, and other waypoints. In some areas, anglers still use the TD pair system in leiu of the Latitude/Longitude format favored among GPS users. Many GPS units will read position in LORAN TD's for those of us that are geographically impaired.
The exact conversion of TD's to geographic position or GP's is difficult and dependant upon several factors including the position involved and the specific model of LORAN. Near perfect results for a batch of numbers within a limited area can be done using a computer program from Andren Software called "LORANGPS". Basically a fix needs to be taken for a test spot within the conversion file area with both LORAN C and GPS. Additional secondary factors or ASF's can then be adjusted in the chosen program until the LORAN and GPS positons match. Once a value for ASF's is attained, it can be applied to all positions within the local area. The result is a group of old LORAN data which can now be used with a GPS.