Navigating waters before GPS: Why some mariners still refer to Loran-C

by Nick Perugini

One of the most popular recurring questions received by NOAA’s Office of Coast Survey involves customers – typically fishermen – wanting to obtain a chart with a Loran-C navigation grid on it. Here are a few inquiries from NOAA’s Nautical Inquiry & Comment System:

  • Hello, I was wondering if it is still possible to purchase or locate older editions of Lake Huron charts (14862-3-4) with the LORAN-C overlay. Many older wrecks and reported snags are still in Loran and have not been converted to GPS. Artificial algorithms are difficult to use when plotting grids. Any help you can give me is much appreciated.
  • Is it possible to access Loran-C charts of New England from prior to 2009 when NOAA stopped published with the LORAN-C lines? THANKS!
  • I was wondering if there was a way for me to buy a chart that has LORAN lines and notes on it? I understand that all of the new charts no longer have this information on them. I am most interested in Chart 11520, Cape Hatteras to Charleston. I didn’t know if there might be an archived form of this chart that shows the LORAN features. Any help in finding a chart like this would be greatly appreciated.

A quick history lesson on Loran-C: Loran (Long range navigation) was a hyperbolic radio navigation system developed in World War II. Loran grid lines (actually hyperbolas) first appeared on nautical charts during the 1950’s. The intersection of these electronic lines of position generated from shore transmitters provided mariners with accurate positions, within hundreds of feet, as their vessels operated nearshore as well as many hundreds of miles offshore. In the 1970’s, the U.S. Coast Guard (USCG) upgraded Loran-A to Loran-C, a system that was even more accurate and much easier to use.

However, positioning technology marches on. With the dawning of a high accuracy Global Positioning System (GPS) in the early 1990s, Loran-C slowly became antiquated and finally the USCG took Loran-C transmitting stations offline in 2010. With no Loran-C signal, Coast Survey followed suit and began to eliminate Loran-C lattices from nautical charts. Most charting customers welcomed the removal of the busy lattices from the chart as it made the chart more readable.

The entrance to the Chesapeake Bay, Chart 12221, with a Loran-C grid on the 2009 edition (left) and without Loran-C (right).
The entrance to the Chesapeake Bay, Chart 12221, with a Loran-C grid on the 2009 edition (left) and without Loran-C (right).

So why do some people still want nautical charts with a Loran-C lattice? Prior to GPS, many fishermen and commercial diving operations did not use a true latitude and longitude (Lat/Lon) geographic coordinate system to position their offshore features. They identified their favorite fishing or diving locations by Loran-C time delay coordinates. When Loran-C lattices were removed from NOAA charts, many fishermen were left with Loran-C coordinates that had no corresponding Lat/Lon. Therefore, they did not have a way of plotting their Loran-C coordinates on current charts.

The Office of Coast Survey Historical Map & Chart Collection provides one way to address the problem. Users can find editions of their charts published prior to 2010 that would likely contain a Loran-C lattice. While historical charts should not be used for navigation today since they have not been updated, they can be used to convert Loran-C coordinates to Lat/Lon (GPS coordinates). Customers can download charts as high-resolution images, transfer the files to a flash drive, and take it to a local printer who can print the charts in a large format. Alternatively, some electronic chart systems allow you to display Loran-C lattices over current up-to-date charts, or to import a chart image, define its Lat/Lon origin, and utilize it with chart plotter software.

So is Loran gone forever? Not quite. In fact, Loran is making a comeback as Enhanced Loran, i.e. “eLoran.” With increased awareness of the vulnerabilities of satellite positioning systems, there is a growing consensus in the national security community that an independent back-up positioning system is required. The USCG and other organizations within the Department of Homeland Security are conducting tests on eLoran. Like the original Loran-C, the new system would have shore-based transmitters that generate hyperbolic grids. Unlike the old system, eLoran would be much more accurate with differential corrections built into the signal transmissions. When and if eLoran comes to fruition, you will not see Loran grid lines returning to NOAA charts since receivers will likely be working in a Lat/Lon coordinate system.

One thought on “Navigating waters before GPS: Why some mariners still refer to Loran-C

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