The Hull Truth - Boating and Fishing Forum

Go Back   The Hull Truth - Boating and Fishing Forum > BOATING FORUMS > The Boating Forum
Search

Notices

Random Quote: You know it's good when she starts cavitatin'.
Closed Thread
 
Thread Tools Search this Thread
Old 08-11-2004, 11:59 AM
  #1    
Senior MemberCaptains Club Member
 
Join Date: Mar 2003
Location: Johnsonville, SC
Posts: 358
Default How accurate are your Loran td to Lat/Lon conversions?

I have aquired several pages of bottom #'s from a commercial fisherman, the bad thing is they are all loran #'s. I have down loaded the POSAID2 conversion program from the USCG site and have been trying to convert the #'s. As you all know, in bottom fishing accuracy is very important so I took the numbers from a wreck that was on the SCDNR site with loran and gps numbers, input the loran numbers into the posaid program and checked to see how close the lat/lon position it gave was to the lat/lon position given by the SCDNR site for the same wreck. There was a difference of over 700 meters!!! Maybe the flaw was using the SCDNR #'s. Has anyone used this program to convert loran numbers they knew were right and checked to see how accurate they were??? I have several hundred numbers to convert, but do not want to waste my time if the conversions are going to be 700 meters off.
reel trick is offline  
Old 08-11-2004, 12:26 PM
  #2    
Senior Member
 
Join Date: Jul 2003
Location: Flowood MS/Orange Beach AL
Posts: 967
Default RE: How accurate are your Loran td to Lat/Lon conversions?

I've tried many and not a one has worked well. They will just drive you crazy.
mscontender is offline  
 
Old 08-11-2004, 12:33 PM
  #3    
MemberCaptains Club Member
 
Join Date: Apr 2002
Location: Mobile-AL
Posts: 34
Default RE: How accurate are your Loran td to Lat/Lon conversions?

My understanding is that the conversion from Loran to Lat/Long is very inaccurate and often reaches one quarter mile inaccuracy... just in the conversion... then you have to remember that the GPS is not 100% accurate either. Loran's repeatable accuracy with the same unit and same antennae is "decent" you should try to buy the old unit from the person who gave you the numbers.
__________________
-- Wahoo! 1850cc with 115 Johnson (1989)
-- 2001 Go-Devil Duck hunting machine! Brigs&Stratton 23 HP air-cooled
will_wahoo is offline  
Old 08-11-2004, 12:38 PM
  #4    
Senior Member
 
Join Date: Dec 2002
Location: Sugar Land, Texas
Posts: 203
Default RE: How accurate are your Loran td to Lat/Lon conversions?

What you need to do is get his Loran as well as the numbers. Run to the location and hit save on the GPS.

I am in the same situation. I acquired more Loran positions than I will ever be able to get to. BUT, I do have a working Furuno LC 90 MkII Loran. I have been cherry picking them as I work known areas.

Good luck with it..........

Bob

__________________
25' Grady White - 2 X Johnson 150 Oceanrunners "Dutch Treat"
Bob VH is offline  
Old 08-11-2004, 12:43 PM
  #5    
Senior MemberCaptains Club Member
 
Join Date: Aug 2002
Location: SW Florida
Posts: 662
Default RE: How accurate are your Loran td to Lat/Lon conversions?

My suggestion is to buy a cheap Loran unit, use it to go to the numbers, verify something is there with your FF, mark that spot on your GPS. Loran requires corrections that vary based on where you are and most of these formulas don't take that into account.
Good luck,
Chris
In Too Deep is offline  
Old 08-11-2004, 12:49 PM
  #6    
Senior MemberCaptains Club Member
 
Join Date: Apr 2003
Location: Houston, Tx
Posts: 1,994
Default RE: How accurate are your Loran td to Lat/Lon conversions?

i just bought the andren conversion software and have been plotting the gps and loran. when i put the same known location on the chart in both formats it is putting them right on top of each other. it seems to work well. you can also plot using both numbers if you have for a location. for $80 i figured i would give it a try. i will let you know how accurate it turns out to be.
AGULHAS is offline  
Old 08-11-2004, 01:07 PM
  #7    
Senior MemberCaptains Club Member
 
Join Date: Apr 2003
Location: Marion, MA
Posts: 950
Default RE: How accurate are your Loran td to Lat/Lon conversions?

Though I've never used it, my Garmin 2010c has the ability to function using Loran TD format.
Recovery Room is offline  
Old 08-11-2004, 01:51 PM
  #8    
Senior MemberCaptains Club Member
 
Join Date: Apr 2004
Location: Merritt Island, FL
Posts: 415
Default RE: How accurate are your Loran td to Lat/Lon conversions?

Adren Software makes a program which converts from TD to LL using calibration data from your area. It has worked pretty well for me but nothing is perfect. With this program you save a couple of point in both the TD and LL formats and the program calculates a converstion based on this data and applies it to all other TD points.

http://www.andren.com/

This program is also great for saving your points, graphing them and gives me the ability to download points directly to/from my GPS .
__________________
Scubadown
1981 Grady White 24 Offshore
1997 200 HP Evinrude

scubadown is offline  
Old 08-11-2004, 01:52 PM
  #9    
Senior Member
 
Join Date: Jul 2004
Location: lawrenceville, ga
Posts: 268
Default RE: How accurate are your Loran td to Lat/Lon conversions?

I think my Lowrance will also convert the numbers although I've never tried it either.

TD
treedawg is offline  
Old 08-11-2004, 02:02 PM
  #10    
Senior MemberCaptains Club Member
 
Join Date: Mar 2004
Location:
Posts: 140
Default RE: How accurate are your Loran td to Lat/Lon conversions?

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

I too have pages of LORAN numbers from commercial fishermen. I have used POSAID2 to convert lat/lon to GPS and compared the results to HOT SPOT maps. HOT SPOT used the conversion program from Andren Software Co. www.andren.com. Consistency between the two is lacking. I can't point to either one and claim that they are on the money. My Garmin hand held has conversion capability. Your note has peaked my curiosity. I'll play with it a bit and see what shakes out.
__________________
--200%Dave
200%Dave is offline  
Old 08-11-2004, 03:47 PM
  #11    
Senior MemberCaptains Club Member
 
Join Date: Jun 2001
Location: Charleston, SC
Posts: 1,200
Default RE: How accurate are your Loran td to Lat/Lon conversions?

For whatever it's worth, the conversion features on GPS units are pretty much worthless. Tried it out w/ some old loran numbers a few weeks back and the conversion on my Garmin was about a half mile off. Really sucks b/c all of my old bottom numbers are in TDs.
The Dude is offline  
Old 08-11-2004, 03:56 PM
  #12    
Senior Member
 
Join Date: Jul 2003
Location: Flowood MS/Orange Beach AL
Posts: 967
Default RE: How accurate are your Loran td to Lat/Lon conversions?

I've used the Andren Software and enjoyed some of its charting abilities, but it was worthless for converting bottom spots. I also had a bear of a time finding and buying a loran, cheap or otherwise. I bought a cheapo model that lasted less than three months.

MScontender
mscontender is offline  
Old 08-11-2004, 04:03 PM
  #13    
Senior MemberCaptains Club Member
 
Join Date: Feb 2001
Location: West Virginia
Posts: 3,877
Default RE: How accurate are your Loran td to Lat/Lon conversions?

It seems to me this is sort of a non-question anyway. What seems to make sense really doesn't have anything to do with a conversion program or where the inaccuracy comes from (the problem is not the conversion formulas or the GPS, its all the LORAN's fault). The real question is how can you use the numbers you have and have to do the least work to get them into a machine where you can use them.

It seems to me your choice is clear. Take your GPS and put it into TD format and then just enter the numbers you have. When you flip it over to LL it will do the conversion. The GPS doesn't actually do a conversion from TD's to LL but that is the effect you see. It won't be any more or less accurate than any other method you use, they will only get you so close, but you weren't going to get any closer than that no matter which type of conversion software you used anyway, and doing it this way you only have to do the data entry one time. So the converted numbers get you close and then you use your depthfinder, or whatever you use, to find the exact special spot and resave it with the push of a button or two. That seems far better to me than entering it once into a conversion program and then seeing the results it give and then re-entering it into the GPS, only then to still have to wonder around a bit to find the target and then resave it. See what I mean?

Oh, on that conversion error, its different depending on where you are. One pretty easy way to tell if your conversions are going to be half way accurate or not is to look at a chart of the area where the TD's are located. See if the light purple lines (TD's) intersect each other at nearly 90 degrees. In some parts of the coast they will make neat little square boxes, and those places the conversions tend to be pretty accurate. On the other hand if they look more like little diamonds, with two large and two small angles, well, the conversion isn't going to be very good..

Thom
Thom is offline  
Old 08-11-2004, 10:13 PM
  #14    
Member
 
Join Date: Apr 2004
Location: johnny walker
Posts: 41
Default RE: How accurate are your Loran td to Lat/Lon conversions?

I have the answer. I use a loran to view my present position when I am near the coordinates. My furuno 1850 gps will display converted td's, I can then open a menu that allows me to "edit" the td's displayed on the furuno gps by adding to or subtracting from the displayed td's. Then I can use the gps to navigate to the Loran coordinates. If I move more than one or two miles I must "edit" the displayed td's again to get a proper fix. Of course the key here is I have the Loran receiver to view true td's. The amount of variance from true td's to gps converted LL to td's is extreme. Sometimes 200 foot error, sometimes .4 mile error. Look at a chart with Loran overlay for the N Gulf(where I fish) and then at S East Florida. The distance between the lines is very different. That means one microsecond of distance is not the same in one area as it is in another. That is why I believe no one conversion is accurate to convert a parabolic coordinate system to a linear system. Bottom line is if you really need some N Gulf numbers accurately converted just email them to me and I will be happy to send you the DGPS corresponding LL. Mark
firstafence is offline  
Old 08-11-2004, 10:47 PM
  #15    
Senior MemberCaptains Club Member
 
Join Date: Apr 2003
Location: Houston, Tx
Posts: 1,994
Default RE: How accurate are your Loran td to Lat/Lon conversions?

i think the accuracy of the conversions might be dependant on where you are. i think they may be more accurate in the gulf.

i am using the adren to chart the numbers (i have about 3000 and they are scattered over a lot of miles) and then i will run them over with the loran and mark on the gps when i pick it up on the bottom.
AGULHAS is offline  
Old 08-12-2004, 06:56 AM
  #16    
Junior Member
 
Join Date: Jul 2004
Location: Port St. Lucie
Posts: 5
Default RE: How accurate are your Loran td to Lat/Lon conversions?

The Coast Guard has a program that is available to the public for converting TD's to Lat/Long haven't used yet, if it is from the CG it should work pretty well link to the program http://www.rdc.uscg.gov/rdcpages/software.html

chris
Loranmk is offline  
Old 08-12-2004, 08:18 AM
  #17    
Senior MemberCaptains Club Member
 
Join Date: Mar 2003
Location: Johnsonville, SC
Posts: 358
Default RE: How accurate are your Loran td to Lat/Lon conversions?

Well, thanks for the response even though it is sad to see that the conversions are pretty much useless. I will have to decide whether to try to install a loran for a while, or sift through the hundreds of numbers and isolate the "clusters" of numbers in a small area, convert them and then use the ff to locate some of the structure.

there are some single numbers in deep water for snowies, tiles, and yellowedge that I really wanted to visit one day.
reel trick is offline  
Old 08-12-2004, 08:28 PM
  #18    
Senior MemberCaptains Club Member
 
Join Date: Jan 2003
Location: Cary/Wrightsville NC
Posts: 1,451
Default RE: How accurate are your Loran td to Lat/Lon conversions?

The best conversion I have seen so far is the Northstar 951XD. Several AR bouys on my last boat came up right on the money when entered as TDs. I believe the unit uses internal ASF tables that take into account the area you are in when doing the math.

My new boat has a Navnet which allows you to apply an offset for your area. I used numbers that are suppose to be good for SE NC but I have not yet confirmed how well the TDs actually convert.
__________________
2004 30' Grady-White Marlin
Megabytes
VHF 68/69
troll is offline  
Old 08-12-2004, 11:45 PM
  #19    
Senior Member
 
Join Date: Feb 2001
Location: Australia
Posts: 2,674
Default RE: How accurate are your Loran td to Lat/Lon conversions?

Right place this time.

Same question, same comments as this one

http://thehulltruth.net/forums/threa...sts=10#M311743

Cheers, Kerry.



Kerry is offline  
Old 08-13-2004, 09:18 AM
  #20    
Senior MemberCaptains Club Member
 
Join Date: Mar 2002
Location: Pensacola, FL
Posts: 4,107
Default RE: How accurate are your Loran td to Lat/Lon conversions?

Quote:
reel trick - 8/12/2004 8:18 AM

Well, thanks for the response even though it is sad to see that the conversions are pretty much useless. I will have to decide whether to try to install a loran for a while, or sift through the hundreds of numbers and isolate the "clusters" of numbers in a small area, convert them and then use the ff to locate some of the structure.

there are some single numbers in deep water for snowies, tiles, and yellowedge that I really wanted to visit one day.
I have much success using the built in conversion on my furuno GP 36. In the upper gulf my loran numbers were always within .05 miles of my GPS conversion. When I got to the conversion point, I would just go to wide cone on my FF and start a search pattern spiraling out from the conversion point. Never took me more than 15-20 minutes to find a number. Mine seems to always be off in the same direction. For what is is worth I have learned that I can input a loran coordinate into my gps, go to the converted number and head NE (40-60 degrees) to find my spot.
DreamWeaver21 is offline  
 
 
Closed Thread

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Garmin 4212 can you toggle from lat/lon to loran td #'s? Ktrain Marine Electronics Forum 3 09-26-2007 01:15 PM
Loran TD's to Lat/Lon conversion trouble cass Marine Electronics Forum 3 01-18-2007 09:27 AM
Lat/Lon Queston saltwaters The Boating Forum 12 09-15-2006 11:46 AM
Converting Loran to Lat/Lon Siv The Boating Forum 20 01-06-2006 03:52 PM
Lat Lon #s for Garmin seanick Marine Electronics Forum 4 11-08-2005 11:08 PM

 



©2009 TheHullTruth.com

Powered by vBulletin® Version 3.7.6
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.2.0