Jeff wrote:


Yes, of course. And now for the third time I'll point out that
noticing the compass bearing of an RDF target change is no more
complex than watching the x-track change.


I agree but if you are starting to drift off your track line, you will
usually pick it up on cross track error well before you see a bearing
change of even one degree.

Of course. I certainly wouldn't argue that RDF and Compass is more
accurate than GPS with x-track. My point is simply that anyone who
would unknowingly "spiral in" on an RDF target probably couldn't be
trusted to understand a GPS either.

If all you do is blindly minimize x-track you might not appreciate
the nature of the current, and how it's affecting other boats.

Actually, my recollection of using RDF is that when we approached a
harbor in limited visibility we made sure that the compass bearing
was shifting in the proper direction, to ensure we were on the proper
side of the transmitter.


That is bush league navigation. You should have been applying the
half convergence correction and steering a compass course.


So? Of course its bush league navigation! What other type did you
expect from a couple of soggy guys on a 24 foot wooden boat a dozen
miles off the Maine coast on a foggy night, with nothing more than a
compass, a Ray Jeff radio, and an old paper chart, probably issued by
Texaco? (The big step up was the spinning light depth sounder!)

And of course the helmsman had a compass course to follow. Are you
actually suggesting that the helmsman was sitting there with the RDF in
his hand? That's the way we do it today, where the helmsman is
surrounded by and array of LCD screens, but it was only a few years ago
that even the smallest boat need a separate nav center down below
because none of the instruments were remotely waterproof.

I'm not familiar with the term "half convergence correction," though I'm
guessing its a method of correcting for the difference between great
circle and rhumb line, and thus of little import to entering a harbor in
a small boat. Perhaps you can explain?

You didn't explain earlier that you were "on a 24 foot wooden boat a
dozen miles off the Maine coast on a foggy night, with nothing more than
a compass, a Ray Jeff radio, and an old paper chart, probably issued by
Texaco?" Half convergence is not important until you are about 100
miles away from the transmitting station. I am trying to explain the
corrections to RDF when used as a nav tool in slightly different
cicumstances. In your case, half convergence doesn't matter and there
is no way of calculating cross track error unless you know the current
or get proper fixes with the RDF. You certainly won't "spiral in" on a
12 mile track.