Eric asked:  What is the bottom line?  Do folks who use radar/electronic
charting overlays like it or are they constantly chasing the alignment
around?

The alignment process is something that has to be done for every RADAR, not
just for overlay on a chart. It's usually only done once, and perhaps
adjusted every few years.  When you overlay the image on a chart, it's much
easier to identify that you have less than optimal alignment, so your
motivated to fix it.  You can use Nobeltec RADAR without a fluxgate compass,
and it will establish alignment with the GPS derived heading information.
However this isn't as good as having an external source for the RADAR image
alignment.  You can use a Dual GPS Heading sensor, or a 10hz Heading sensor,
or the fluxgate compass from the autopilot, each works, with varying degree
of accuracy.

The great thing about a RADAR overlay solution is you have the best of both
worlds.  If you don't like the overlay, just open up a dedicated window.  I
really like the overlay because there is so much more meaningful information
you can discern.  For instance, if you pick up a return, but it's hard to
visually locate it, using the underlying chart info will provide more
topographical information to assist in locating the target.  It is also
easier to discern buoys or markers, because they end up right on top of the
image on the chart.  It's easy to identify traffic in the shipping lanes,
ferry lanes and many other places where the chart provides corroborating
information.  And if it's too much to take in, just use the dedicated RADAR
image, or hit the space bar and all the information on the screen is removed
except the landmass, water and radar returns.

The question I asked wasn't about aligning the RADAR image, it was "How do
people on long voyages manage their equipment settings as the variation
changes"?  Do they just update it as needed, every week or so, once a month,
or when they remember?  Is it part of a log that is used to keep track of a
number of other issues like this as you travel the globe?  If anyone on the
list has real world experience it would be helpful to know how this is
managed.  Thanks!  Scott

Scott Bulger
Knot@Work, 31' Camano

Email:  scottebulger@comcast.net

Scott, I was pretty sure those who jumped on the image alignment issue had
missed your question, but I'm not convinced I fully understand what it is
you're after.  You ask: "How do people on long voyages manage their
equipment settings as the variation changes"?  I guess I just miss the
point.  I don't have anything set on my radar/chartplotter/GPS to convert
magnetic headings, bearings or tracks to True, so they always display in
Magnetic information.  And since the GPS knows where we are and uses that
information to calculate the local variation, I don't have to do any manual
recalibration whenever I travel a significant distance.  Is that the issue
you are asking about?

Bob Peterson
47' Lien Hwa CMY
"Lopaka Nane"
San Francisco

-----Original Message-----
From: Scott Bulger
Sent: Sunday, October 17, 2004 10:16 PM
To: trawlers-and-trawlering@lists.samurai.com
Subject: RE: T&T: Circumnavigation, Electronic Charting & Magnetic

Eric asked:  What is the bottom line?  Do folks who use radar/electronic
charting overlays like it or are they constantly chasing the alignment
around?

The question I asked wasn't about aligning the RADAR image, it was "How do
people on long voyages manage their equipment settings as the variation
changes"?  Do they just update it as needed, every week or so, once a month,
or when they remember?  Is it part of a log that is used to keep track of a
number of other issues like this as you travel the globe?  If anyone on the
list has real world experience it would be helpful to know how this is
managed.  Thanks!  Scott

Scott Bulger
Knot@Work, 31' Camano