Jeff wrote in :

The same will happen with a GPS, unless you know how to use cross
track error. And its certainly better than simply following a compass
bearing.



It will? How's that? My GPS has a few chart plotters connected to it.
They all have at least one, even without the chart plug. You know where
the waypoint is. It draws a line you follow, even if you're steering it by
hand.

How do you spiral in with this? You might be looking at the wrong display!

Larry wrote:
Jeff wrote in :


The same will happen with a GPS, unless you know how to use cross
track error. And its certainly better than simply following a compass
bearing.




It will? How's that? My GPS has a few chart plotters connected to it.
They all have at least one, even without the chart plug. You know where
the waypoint is. It draws a line you follow, even if you're steering it by
hand.

How do you spiral in with this? You might be looking at the wrong display!


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.

On Thu, 09 Mar 2006 22:33:00 -0500, Jeff wrote:

Ah! So you're claiming that a GPS isn't really a GPS unless it has a
chartplotter, or two.

Even the simplest handheld will have a cross track error function
these days. Anyone who doesn't know what it is, or how to use it
really does not belong in a situation where navigation is required.

Wayne.B wrote:
On Thu, 09 Mar 2006 22:33:00 -0500, Jeff wrote:


Ah! So you're claiming that a GPS isn't really a GPS unless it has a
chartplotter, or two.


Even the simplest handheld will have a cross track error function
these days. Anyone who doesn't know what it is, or how to use it
really does not belong in a situation where navigation is required.

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.

The ability to connect a GPS to an Autopilot and track a straight line
across a current is real spiffy. Being able to do it manually by
understanding what's going on around you is even better.

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.

Larry wrote:
RDF is great as long as there is NO DRIFT, water current or wind drift.

If you don't learn to take that into account and just follow the RDF to the
station, you end up in this big spiral to the target, the long way around!

GPS, of course, doesn't suffer these 1930's problems.


Well, all it's doing is solving the relative bearing drift
for you. If a person doesn't know how to do this for
themselves, then they can't navigate. Period. It's one of
the basic skills.

Of course, under most circumstances you can let the machine
do it for you. But I'm of the old school that says it's
better to know how, yourself.

Another poster here said, a long time ago: "When people
complain that learning to navigate the old-fashioned way is
difficult, slow, & boring, you can always answer that
crashing your boat into the rocks is easy, fast, and
exciting!" It's the best answer I've heard.

Fresh Breezes- Doug King

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.

DSK wrote:
Larry wrote:

RDF is great as long as there is NO DRIFT, water current or wind drift.

If you don't learn to take that into account and just follow the RDF
to the station, you end up in this big spiral to the target, the long
way around!

GPS, of course, doesn't suffer these 1930's problems.


Well, all it's doing is solving the relative bearing drift for you. If a
person doesn't know how to do this for themselves, then they can't
navigate. Period. It's one of the basic skills.

Of course, under most circumstances you can let the machine do it for
you. But I'm of the old school that says it's better to know how, yourself.

Another poster here said, a long time ago: "When people complain that
learning to navigate the old-fashioned way is difficult, slow, & boring,
you can always answer that crashing your boat into the rocks is easy,
fast, and exciting!" It's the best answer I've heard.

Fresh Breezes- Doug King

When you take a bearing using RDF of a coast station that you want to
get to you don't steer the bearing on the RDF. That bearing is called a
"curve of constant bearing" and is only part of the solution. The
curve of constant bearing can be either north or south of the actual
bearing to the station unless both the ship and the station are either
on the equator or on the same longitude. What you have to apply to any
other bearing to get the Rhumb line is half convergency. That will give
you the course to steer.

The same problem applies when using RDF bearings to plot a fix. Those
are not straight lines from the radio station but curves of constant
bearing and the resolution of the fix becomes a sperical trig problem
unless you use the half convergency tables to correct those bearings.
Of course the closer you are to the radio station the less the correction.

GPS is better, way better.

Gaz

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.

otnmbrd wrote:
Wayne.B wrote in
news

On Mon, 06 Mar 2006 05:01:05 GMT, otnmbrd
wrote:


Gee, I wonder how I navigated all over the world, offshore, prior to
GPS, if I had no viable alternative to GPS.

Probably celestial and DR unless you were lucky enough to be on a ship
with a good inertial system.

Tell us about the times when you couldn't get a celestial fix because
of clouds.




First off remember..... you're offshore. Although it's great to know
exactly where you are at all times, for much of your trip it's not really
necessary and even when things were great for celestial you only got three
"exact" fixes every day ... morning/evening stars and noon.
Sure there are times when you don't get a fix for extended periods and
anyone can tell of cases where this caused a grounding, etc., but for the
most part you were and are able to use your knowledge of your boat's
reaction to weather, known currents, etc. to maintain a reasonable DR until
you do get a sight, come on soundings, approach land, etc.
You use whatever is there.
The problem with the sole reliance on GPS or multiple GPS is that you
become a "mechanical" navigator and either forget how to use other methods
or never learn them to begin with, which can rear up and bite you on the
butt when the bananas hit the fan.

otn
Although a yachtie or freighter may not have cared where they were all
the time, that was not everyone's attitude. Take a military example
where you have to rendezvous with another ship or submarine in mid
ocean. A few miles could mean disaster. Take the search and rescue
problem. Same thing. What about the research done on specific things
on the bottom? GPS has facilitated accurate navigation to a degree that
was only dreamed of in the past. It should be your first line piece of
kit when offshore, not at the exculsion of anything else but certainly
head and shoulders above all the rest.
In my opinion the only better way to navigate is by visual fix or radar
fix. Even then I check the fixes against GPS.

Gaz