NavList:

Bill wrote:


> The crew decided to crank it up, mostly out of curiosity I suppose, and it
> was 10' off on both lat and lon.  We grabbed the manual and went about
> setting it up from scratch.  I read, my buddy tweaked.  Fired it up and same
> results.  So my buddy read and I tweaked.  Same results.  My guess, some
> sort of antenna problem (short, open).

Lu replied:

It's maybe too late to know this, but I'd be curious about a couple of
things:

1)  How old was the Loran?

2)  Were the readings consistently off by always a certain amount, or
were they randomly off?

Bill guesses:

Working from memory (this would have been the 2004 Great Lake's season):

1. No way to know at this point the age of the unit.  Came with the used 34,
and I don't recall the boat's vintage.  The unit/supplied manual was set up
to read off in TD's or directly in lat and lon if that helps place its date
of manufacture.

2.  It/they seemed to be consistently off, but by a ton.  10' lat and 10'
lon.

I did recall when GPS arrived on the scene, pre fancy antennas, parallel
processing, DGPS, WAAS, and SA on or off that the common wisdom was if you
had never been there, GPS was better at locating the spot.  If you had been
there and marked a waypoint at a buoy, be careful you don't run over the
buoy on the return trip.  This was due to the effects you mentioned, "I
guess that the unit didn't correct for ASF (variation in the speed of radio
propagation as the signal travels over land or water)." I would add to that
radio waves being bounced off bluffs, structures etc.  How could the unit
know in those days?  But once it had been there and was told the location,
it factored in all that double-E stuff. All it had to do was recognize the
pattern it saw before at point A.  Yep, same pattern, so I must be at point
A.  Auto IC ;-)

I am not clear what was wrong in our situation. The Great Lakes, as I
understood it, had a pretty good selection of masters and slaves (lots of
chains) and very good signals. I could accept a fraction of a mile, but up
to 10 nautical miles?  Not good.

I recall reading articles on folks testing antenna leads with multimeters if
the LORAN readings went south, and that was often the problem.  I don't know
if something was fried or off spec in the unit's little brain, or if there
was an antenna/antenna lead problem, or both.  (What the heck, it "worked."
<G>) The owner traded up to a brand-new Catalina 350 that winter, so the
problem literally went away.  With it the chance to do some trouble shooting
and learn from the experience.

I muse about recounting these tales to children or grandchildren who grew up
with gaming, high-speed internet, and GPS.  "Well little Ted, people sat and
looked at scopes to see the difference in the time it took radio waves from
various starting points to get to them."  Blank stare.  "OK. Marilyn Monroe
and two clones start running toward me from different locations.  Being
duplicates, their speed is the same.  So I can tell how far I am from the
point each Marilyn started from how long each one took to get to me."  Then
little Ted says, "That's pretty neat grandpa, I know what a clone is, but
what's a Marilyn Monroe?  Was she like Laura in Tomb Raiders?"

Which begs the question, how much longer will they continue to put LORAN
lines on charts?

Bill

=========================
The reasons for these questions is that they remind me of my first
Loran, purchased in the early 1980s.    It was a Furuno unit.  I'm an
electrical engineer, and the insides of the box were truly magnificently
constructed.  Proverbial brick outhouse.   I think the base price of the
unit was around $1200, but I paid an extra $500 to get the "upgrade" to
have it display latitude and longitude rather than TDs.

After I installed it I discovered the L/Lo readings were off by about
1/4 mile.   After learning the fine grain details of the workings of
Loran many years later (and, by the way, the US Government's Loran User
Handbook is way better than the GPS handbook in explaining the
technology to someone who is technically knowledgeable), I guess that
the unit didn't correct for ASF (variation in the speed of radio
propagation as the signal travels over land or water).

The good news, though, was that the unit was CONSISTENTLY off.  If it's
longitude readout was off by 0.25 minutes at a known location, the
readout would be off by the same amount at all nearby locations.

Well, all I had to do is treat this like IE on a sextant.  If I wanted
to get to a new waypoint, all I had to do is measure its L/Lo and then
adjust the numbers for the loran's "offness" before entering them as
waypoints.

I successfully used this beast navigating in thick Maine fogs for many
years, always hitting desired points within 50 feet or so.

The poor Furuno died after a dozen years (just before GPS became
popular) and I replaced it with a Micrologic unit (speaking of the
dead).  It was 1/10 the size of the Furuno, had many more functions, and
L/Lo readings accurate to 0.01 of a degree (at least on the East Coast
of the US where the crossing angles are better).

But I missed the challenge of the old Furuno.  Maybe I shouldn't
castigate George for his old-fashioned ways so badly....

Lu Abel


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