Given that the objective is to locate, identify, and determine accurate Lat/Lon coordinates for the thousands upon thousands of time difference coordinates that were gathered, and recorded, by several generations of local fishermen, I've got good news, and I've got bad news. The good news is, "There is a way to do it;" the bad news is, "There is only one way, and it's not going to be simple, or easy."

Succinctly put, the target areas identified by time difference coordinates must be re-located by means of the same LORAN technology that recorded their position to begin with. Then, a new GPS/WAAS receiver can be used to record an accurate Lat/Lon position that should allow you to return to that spot indefinitely, and/or share it with others.

For most people trying to find these fishing/diving "hot spots," that is going to sound significantly easier than it will ultimately prove to be.

Unfortunately, someone seems to have convinced the general public that LORAN is an antiquated system, and many people believe it has been shut down. Although neither is true, this general and widespread perception has dramatically impacted the market. Virtually every marine electronics manufacturer quit selling LORAN receivers.

Therefore, the first problem for those wishing to hunt down these old time difference coordinates will be finding a functional LORAN receiver, and a matched coupler. Fortunately, new couplers can still be ordered for old receivers.

I personally use an old Si-Tex 787C, but almost any similar unit available on e-Bay will work as well. Be careful when you see old Si-Tex LORANs with "XJ" designators. The XJ1 and XJ9 were excellent units, but XJ units with numbers between 1 and 9 (such as XJ2) were "odd-ball" units that incorporated some sort of architecture by Ross. I don't suggest that they aren't reliable, but they will not take you to the same place as was recorded by any other Si-Tex LORAN.

There appears to be good news on the horizon.

As I said in my introduction to this project,

"Shopping for a LORAN these days is about like shopping for an 8-Track player . . . Mark my words -- that will change."

I said that because the Coast Guard has been pouring money into upgrading the LORAN system and the Department of Homeland Security is pushing it - along with virtually everybody who is anybody from MIT to the Royal Navy. Based upon my research and everything I was reading, I believed (and continue to believe) that LORAN is going to be the focus of a great deal of renewed attention.

And so it has. Si-Tex Marine recently announced the reintroduction of LORAN into their product line - you can read their announcement here:

http://www.si-tex.com/html/new_secure_navigation_system.html

In order to visualize the reason why LORAN must be used to chase down LORAN coordinates, and understand why LORAN continues to be viable technology, I refer you to a scatterplot published by MIT. A picture is truly worth a thousand words. Those of us who have used this equipment know that there is a certain amount of "dither" inherent in these systems. This is what you get when you plot the GPS and LORAN fixes of a STATIONARY object over a 24 HR period.

This tells the whole story eloquently. Study the scatter plot and note the following:

1) GPS is much more accurate than LORAN. Throughout the 24 HR period, the GPS receiver reported fluctuating positions, but the reported position was always within 100 meters of it's true location and usually within 25 meters.

2) Although the LORAN receiver thought it was about 180 meters southeast of it's true position (measure to zero point at center of chart), it was much more consistent; it reported position fluctuations of no more than 15 meters in any direction.

3) It would be futile to try and use the GPS to return to the position marked by the LORAN - you could be as much as 240 meters off (measure from extremes of each plot).

4) It could be frustrating to try and use the GPS to return to the position marked by the GPS - you could be off by as much as 150 meters (measure between extremes of GPS plot).

5) It would be simple to use the LORAN to return to a position marked with the LORAN. You could expect to return to the same position within 25 meters (measure between extremes of LORAN plot).

In actuality, the difference is not as extreme as this scatterplot depicts - the GPS plots were adversely effected by selective availability (SA) and the LORAN plots were generated without the benefit of ASF correction. I'll further address those issues when I discuss the use of this equipment in an upcoming report.

The point is, these are very different, complimentary technologies. High frequency, low power, airwave signal propagation versus low frequency, high power groundwave signal propagation. Considering the critical significance to aviation and marine navigation, why would the government abandon a reliable secondary system like LORAN? They won't.

The potential here is especially obvious to any marksman who understands the principal of "Kentucky Windage." Look at the scatter plot again and imagine that it represents a rifle target. Bear in mind that GPS makes it possible to precisely correct for the LORAN's inherent error - imagine what you would get if you "zeroed" the LORAN rifle scope, adjusting it 137 meters west and 137 meters north!

Over the last ten years, the public's infatuation with new technology has knocked the bottom out of the LORAN industry, but Si-Tex is returning to it, and I believe that you can expect that the other major manufacturers of marine related equipment will follow suit - although what the others do probably won't matter to me, or anyone trying to do what I am doing.

I say that because I had occasion to be aboard a lot of boats during the course of my marine law enforcement career, so I know for certain that most of the local commercial fishermen have always relied heavily on Si-Tex equipment - probably as much as ten-to-one. Therefore, most of the time difference LORAN coordinates in circulation here in SW Florida were recorded with Si-Tex equipment.

If the new Si-Tex LORAN/GPS/WAAS receivers report the same TD's as the old ones did, it will be a one-stop shopping answer to the first part of the problem, and I have no reason to suspect that this will not be the case. At any rate, I will have one of these new LORANs on my boat just as soon as they hit the street; I'll operate it alongside my venerable 787 and find out whether it can be used to run down old numbers.

I'll report back on that so stay tuned!

So, to Jim Jones, at Walker's Marine, I would say that with regard to this first aspect of the situation, you can tell your Clients that it boils down to this:

Anyone who hopes to run down the old time difference coordinates needs a functional LORAN receiver, coupler and the readily available whip antenna. They can either buy used equipment and take their chances, or wait a month or so until the new Si-Tex units become available.

In the meantime, it might be wise for them to give the SONAR issue some thought. Whether they attempt to use LORAN, GPS, DGPS, WAAS, or good old fashioned haruspicy as their guide to navigation, they will need an effective "bottom machine" to see what's down there, when they get there.

That will be the subject of my next article.

I will address the use of this equipment once we have it all introduced, and identified.

I welcome your comments, questions and suggestions.