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Loran questions

Old 12-07-2002, 11:57 AM
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I just bought a used interphase pilot loran 2 so I can convert all my TDs to my GPS.

Questions I have, it says I need to mount my antenna 6 feet away from my VHF antenna which is impossible since I have a 22' center with no T-Top, I can get about 3 feet but that puts me right next to my fishfinder, is this going to be a big problem?

Second question, whats the differnce between loran and loran C?

I used a loran about 10 years ago, and when we would come close to a number, we would use a chart which would tell us which direction would make the last two number gain, lose or hold. The person I bought this from says you dont have to do that with this unit, why is that?

Thanks for any help anyone can provide.
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Old 12-07-2002, 12:44 PM
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I'll try to get started... What GPS do you have? Most of the newer Garmin models will allow you to convert TDs to Lat/Lon. Not a perfect conversion, but close. I assume, you'll convert TDs to Lat/Lon then enter the Lat/Lon in the GPS? A lot of work. I do not know the difference between Loran and Loran C. I believe what you are referring is the Lorans ability to run your boat down a Loran line (X, Y, or Z) as I remember, keeping one set of Loran lines figures constant, etc. You'll still be able to do this on the Loran...but the question is: with the GPS why would you want/need to do this any more?. That ability with the Loran was somewhat of a navigational convience; no more. [img]/infopop/emoticons/icon_wink.gif[/img]
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Old 12-07-2002, 01:50 PM
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I have a brand new 182c GPS, problem is, converting just isnt even close. Its frustrating to spend 6 hours looking for numbers and 2 hours fishing.

Now, ill just put in the TD into the loran, go there, mark it with GPS once I find it, and its done forever.
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Old 12-07-2002, 03:04 PM
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That's where I thought you were going. Nothings perfect. Have fun. [img]/infopop/emoticons/icon_frown.gif[/img] [img]/infopop/emoticons/icon_wink.gif[/img]
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Old 12-07-2002, 10:19 PM
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Thom, I'd like your expert opinion on this one if you get a chance [img]/infopop/emoticons/icon_smile.gif[/img]
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Old 12-08-2002, 05:41 AM
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Simba, a friend has the Garmin 152 on his boat. It has the loran offsets in it. His loran and GPS track right together. Look in your menu for the T/D offsets. Now where you are going to get the ofsets is a different story. Find someone with the offsets in thier unit and get along side, this will get you going.
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Old 12-08-2002, 07:23 AM
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Simba,

Back to the first question. You should be OK at the 3 foot mounting. I've had them as close as 4 feet to VHF antennas without doing any damage to the LORAN myself (long long ago thankfully).

As to the conversions, well, that's just the way it goes. If you are in an area where the TD lines cross each other at near a 90 degree angle the conversions tend to be a lot closer to the mark, but that's just not how it goes for some areas. You might want to take a look at the chart for your favorite fishing grounds and see if you can change secondaries and get a better intersect between the TD's, that sometimes helps. In the end though the real problem is not with the conversion program and its not with the GPS. The real problem is with the initial positon inaccuracy of the LORAN system. Remember, LORAN is just great at getting you back to a point you've already visited, usually within a circle measured in feet, but it has the potential to be absolutly lousy at finding a spot with a known location in the first place. Even the Coast Guard never allowed the companys selling them (there were a lot fewer manufacturers of LORANS then there ever were companys selling them under their own names) to advertise that they were more accurate than down to a quarter mile - really!

Good luck with your conversion. I will tell you that when I bought my first GPS it did not have conversion capability and I found myself plotting TD's on a chart and then converting them from the chart to LAT/LON and entering that info into the GPS. It did not work real well, but it was all I had at the time. Then I used the Coast Guard's PosiAid-II for a while, and found it no better. So it goes. Now days, because TD's tend to be used in radio conversations where I fish, I keep one GPS set in Lat/Lon and the other in TD's while we are out there playing Sportsman. Its not really necessary, cause you get it in your head where you are after 10 or 20 years, but it gives me a rosy feeling to see it [img]/infopop/emoticons/icon_razz.gif[/img]

Thom

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Old 12-08-2002, 09:36 PM
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Your statement that the TD -> Lat/Lon conversion "isn't even close", is unfortunately, the norm with LORAN. Thom's observation about precision (returning to a previously recorded spot) as opposed to absolute positional accuracy really says it all. There is however, a simple way to correct the conversions. This method was used by most of the calculater-based LORAN navitation programs that were available in the late 70's and 80's. It is based on the observation that based upon a single calibration point, one can "warp" the observed TD's in just the right direction and magnitude to yield accurate Lat/Lon values within a limited geographical area surrounding that point. In practice, it's fairly simple to do. One must have the measured TD of a known landmark (hopefully, the precise geopgraphic location of one or more of your previously stored waypoints is known with certainty; e.g., a channel marker, etc.), the calculated TD's (your Garmin 182 will calc' these) and the actual Lat/Lon for a calibration point (obtained from a chart, or supplied by your Garmin GPS). Conservatively, correction values from a single calibration point should provide acceptable accuracy within a radius of approximately 25 miles of the calibration point. For each calibration point, simply calculate the difference between the actual and calculated TD's for each Master/Slave station pair. These two numbers serve as correction factors. Apply these correction factors to any of your previously measured TD's within the limited geographical area around the calibration point. Enter the corrected TD's into the Garmin and the resulting calculated Lat/Lon should be quite accurate. The accuracy of this method is dependent upon Master/Slave station geometry as well as location within the coverage area, but if you are anywhere on the East Coast, it should work quite well.
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Old 12-09-2002, 09:59 AM
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I spent about 3 mo early this year doing research and converting 400 old loran #s to L/L. I have 3 GPS unit with conversion capability--- wrong answer on all. I am in a bad relative location due to angle of loran TDLs (see Thoms comments above). After much head scratching I used a program that corrected the TDs with the Navy ASFs, a measurement last done in 1990. I also purchased an old loran unit to be sure I could get to the old "hot spots". I will start verifying the conversions on the next fishing trip and will let those interested know how it came out. I guess my biggest worry isn't the conversion but the accuracy of some of the initial readings. I have found fairly large errors in published numbers. This was probably due to bad conversion by someone without noteing the original source no. In one case the DNR # missed the Navy tower by about 10 mi.
Thats why the chart disclaimers.
Joe

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Old 12-09-2002, 11:32 AM
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Cadjh ,has it right as to figuring the offset factors. I recommend you use an object that does'nt move like a light tower or channel range. Buoys aren't as accurate as they move with the current. Once you establish the factors then you can use a known reference point to use when you restart the unit As far as the vhf being close to the loran antenna, the only problem you may have is if you use the radio while having a weak loran signal. The use of the vhf in this circumstance could cause you to lose your loran signal momentarily. I really wish someone made an eletronic loran chartplotter, as finding your position on a chart with loran is much easier than with GPS. And to tell you the truth I don't think the loran will ever be phased out. The electronics companies have been preparing for the phase out for over ten years and they continue to extend the phase out dates.


Good Luck

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Old 12-09-2002, 05:08 PM
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Simba,
Before GPS when I used Loran C I had my Loran antenna approx 2 1/2" from my VHF antenna and had no problems. Good luck

"Snow Goose", John Jensen
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