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. Here in the Chesapeake LORAN operated on the
9960 Chain 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. Popularity of LORAN equipment never regained it's momentum
and eventually the system was shut down.
LORAN-C has several
characteristics that make less attractive than the new GPS equipment. LORAN
needs a bulky antenna, making portable units impractical. Other disadvantages
are the need for specialized charts, area specific coverage and LORAN's tendency
to shut down during electrical storms.
Most old timers have a crumpled old book
filled with pairs of LORAN TD's for every manner of fishing spot, wreck, buoy
and the like. 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 the LORAN
and a 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.
LORAN navigation systems are explained in detail by this Garmin
LORAN TD Position Handbook.