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> Loran-C TD Conversion toL/L
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post Aug 15 2002, 08:50 PM
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Over the years I have collected quite a few loran TD's of unpublished sites. I recently began attempting to convert them to L/L. What a mess!
I purchased a CD program called GPS LORAN Locker. It has the ability to use asf correction factors based upon the Navy chart adjustments. To make a long story short I attempted to check the conversion by converting known tower TD's. TILT! Most printed tower locations appear
incorrectly translated or the Vault is a bust. I then found a book by Captain Rod and Susie Stebbins entitled Coastal Loran & GPS Coordinates. The L/L and TD's for the tower locations off the Ga. coast don't match most locally published #'s. The Vault conversion hower, works perfectly with the Stebbens' book numbers.
HELP! Anyone had this experience (the loran went with the old boat).
Anyone got a good loran for sale? GPS units don't correct closer than .25 mi.
Tight Lines
Joe
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reeljustice
post Aug 15 2002, 09:18 PM
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Joe, I didn't do too well in math in high school and avoided it almost completely in college, so, I can't explain all the details. But, I'll give it a shot as best I know it.

The conversion programs you talked about are composed of alogorithims. Since the earth is round, there is no simple formula to convert a TD to a Lat/Lon. Notice on your maps that the distance between the longitude lines are very wide near the equator, but, very close near the poles. The alogorithims have to account for these differences, depending on the exact location on the earth. That is why you have the ASF corrections.

I am told that the most accurate alogorithim had the ASFs every 4 minutes or 4 seconds. That was/is the Fisherman's Black Book in the old C2C program. It is my understanding that program is still available when you join the Bluewater Fishfinder (formerly C2C). I forget the name they call it now, but, it's still the same thing.

I can tell you that I have used Loran GPS, Fisherman's Black Book, Posaid and a few other conversion programs. Black Book gave me the best results, but, I still always had to search around for the EXACT spot once I got to the general area to find the spot and re-mark it with the GPS.

So, use the conversions to get as close as you can, throw out a buoy and begin an ever-widening circular search pattern until you find your spot and mark it with your GPS. Slow, but, the only way I know.

Tight lines,
Joel


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Guest_Brad_*
post Aug 16 2002, 06:47 AM
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There is a program that the Coast Guard uses called POSAID. That's one that Joel mentioned. It is a conversion program for Loran to L/L. I fish with some guys on the Gulf side that use it for conversions. There is some tweaking that has to be done, but the master of POSAID, Grouper Sandwich, on the Florida Sportsman board Northwest section usually gets the numbers to within 200 feet.

If you download that program, I can hook you two up and he can give you a brief tutorial on how it's done. He's made some changes from the directions included with the download.

Edit: Here is the link to POSAID

http://www.rdc.uscg.gov/rdcpages/soft-posaid2.html

Let me know,

Brad
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GunDog
post Aug 16 2002, 09:19 AM
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I don't know if this will help or not but figured I'd throw it out there. I purchased a newer model Locan-C for "The Buddies" that does this for you. According to the book that came with it, it claims that it can put you back with-in +/- 25' of the waypoint that has been recalled, in TD's or L/L. But then on the next sentence it states that it is not absolute? I don't know, but have had real good luck at returning to different structure on the bottom with it when recalled. We still run in circles but seem to narrow them down to a great extint. I have noticed that running both the loran-c and gps does help in our setup, for what it's worth. GDog


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pop
post Aug 16 2002, 12:28 PM
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Thanks for the thoughts guys.
I downloaded POSAID, a dos progran written in the 60's.(our gov.at work).
It works but won't use the Navy asf adjustment factors. I think I just solved the problen, ordered a used Furuno LC-90 over the net. I think we still have some problems with the Ga. published L/L and TD #s though.
The Sapelo Cat had to go back to Riverside Al. for some minor warranty work but I plan to have her back in the water by labor day. With two WAAS GPS units and an old loran, I should be able to get to the bottom of the published number problem(a little at a time). I'll let you know what I find.
Thanks Again
Joe
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