Gary wrote:
Jeff wrote:

Wayne.B wrote:

On Fri, 10 Mar 2006 08:19:30 -0500, 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?

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.

On Fri, 10 Mar 2006 22:27:04 GMT, Gary wrote:

You certainly won't "spiral in" on a
12 mile track.

Hopefully we all agree on that.

There were a couple of times I was glad to have my old Ray Jeff RDF on
board but I am no more eager to dust it off and use it again, than I
am to do long division by hand.

Gary wrote:
....
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.

Well, I did specify "entering a harbor" and this sub-thread was
triggered by Larry's comment about "spiraling in" in a cross current,
which would not likely be an insurmountable problem for a professional
on a large ship 100 miles off (or even an amateur, back in the day).

The problem of spiraling certainly does happen on short trips.
Consider the crossing from Wood's Hole to Martha's Vineyard, about 3.5
miles across Vineyard Sound, which often has a 2.5 knot current. If
you simply "home in" on the West Chop Lighthouse (or a hypothetical
radiobeacon at that spot) you could find yourself halfway to
Nantucket, downwind, and with a nasty chop in your face. (Don't ask
how I know this ...) This little passage can be particularly
vexatious because there are almost always 2 or 3 ferries crossing,
which are usually pointed one way, but headed another.

Wayne.B wrote:
On Fri, 10 Mar 2006 22:27:04 GMT, Gary wrote:


You certainly won't "spiral in" on a
12 mile track.


Hopefully we all agree on that.

What kind of boats do you guys have??? You sound like a powerboater
claiming you don't have to think about currents because you're doing
30 knots all the time.

Where I sail there are frequently currents of 2 knots or more, plenty
to cause "spiral" for a slower sailboat.



There were a couple of times I was glad to have my old Ray Jeff RDF on
board but I am no more eager to dust it off and use it again, than I
am to do long division by hand.


I'm guessing I'm one of the few here that actually remembers how to
take square roots long hand.

Jeff wrote in :

Ah! So you're claiming that a GPS isn't really a GPS unless it has a
chartplotter, or two. Sorry, I didn't understand. And you know
you're being set because that little picture of a boat keeps drifting
off to one side. This is completely different from using RDF and
compass, where the compass bearing will keep shifting to one side.



Any GPS that has a DISPLAY is, by definition, a chart plotter. I don't
know of a single, cheap, even handheld GPS that doesn't have a plotter I
can put a waypoint into. There's none on the Raymarine Raystar 120, as
it's a feeder GPS for the Seatalk network, which has a display, which is a
chartplotter.....

NO RDF has any kind of a plotter I ever saw. It points to the station on
the null, duhh..

Why are we having this stupid troll? RDF is useless, now, a waste of
space. Use it to weight down the trash when you dump it overboard.

No, I don't have an astrolabe aboard, either!

Jeff wrote in
:

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 they should be arrested for stupidity as soon as they hit the dock.

On Fri, 10 Mar 2006 19:23:54 -0500, Jeff wrote:

What kind of boats do you guys have??? You sound like a powerboater
claiming you don't have to think about currents because you're doing
30 knots all the time.

Where I sail there are frequently currents of 2 knots or more, plenty
to cause "spiral" for a slower sailboat.

You're doing something wrong. Before you start, first solve the
current vector problem using an estimated speed for your boat and the
average current speed/direction from your tide tables. Use that as
your initial offset to the rhumb line course direction. Once enroute
check the bearing to your destination using the weapon of your choice
- bearing compass, RDF, whatever. Your bearing should stay constant
if your offset is correct, otherwise make a correction plus or minus
and continue to recheck. There is really no excuse for being
accidently swept down current, even in Vineyard Sound.

Gary wrote in news:aKiQf.130233$sa3.77836@pd7tw1no:

GPS is better, way better.



They remind me of my old ham buddies clutching onto their Morse keys as if
their very lives depended on it. "You can always get through on Morse when
nothing else works.", they assure anyone listening.

That's when I bring them in to watch what happens with PSK31, a new amateur
radio text mode that uses just the sound card and an SSB receiver. It
copies THREE signals slightly off each others frequencies
SIMULTANEOUSLY....signals you can't even detect with your ears...MORSE
ears.

Don't forget to tow your horse trailer, either. You never know when your
car might conk out and strand you! Having the horses in the trailer will
allow you to fall back on older technology.

There's 3 handheld GPSs, not counting what any guests bring, and two
mounted 12V GPSs on Lionheart. There's 4 chart plotters if you count the
Yeoman marking the paper chart from them. I can flip some little toggle
switches in the NMEA network and force GPS data to power the network if any
component, like the multiplexer, should fail. I'd say we have a fair
number of backup systems in case anything short of EMP from a nuclear
strike happens, in which case navigation won't be much of an issue....

Sure wish he'd get the AIS transponder, soon.....(c;

Larry wrote in
:

There's 3 handheld GPSs, not counting what any guests bring, and two
mounted 12V GPSs on Lionheart. There's 4 chart plotters if you count
the Yeoman marking the paper chart from them. I can flip some little
toggle switches in the NMEA network and force GPS data to power the
network if any component, like the multiplexer, should fail. I'd say
we have a fair number of backup systems in case anything short of EMP
from a nuclear strike happens, in which case navigation won't be much
of an issue....



Crap....that isn't the correct number. I forgot to count the GPS receiver
in the 406 Mhz EPIRB in the ditch bag....