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From: Faure, Marin (no email)
Date: Fri Jul 02 2004 - 13:15:09 EDT
Perhaps I'm overly influenced by my experience in aviation, but I
believe that being able to overlay a radar (and wx radar) picture over a
positional picture is far superior to having separate displays for both.
When you think about it, the whole idea of radar is to give you a
"picture" of what's out there. Unfortunately, the nature of radar is
such that it can only paint things that reflect the radar signal. Plus
with the kind of radar we use, it doesn't tell you much, if anything,
about the return it's getting. So even with a stand-alone unit-- like
the old Raytheon 2600 on our boat-- you end up mentally "painting in" a
lot of the same information that's on a chart.
You see a target marking a buoy in the middle a shipping channel. I
wager to bet that you're mentally painting the boundaries of the
shipping channel as you're looking at the radar picture. Or you see the
return that you know is the point of land you're going to go around.
The radar doesn't show it, but you know the bay you're headed for is on
the other side of the point and you mentally project the location of the
bay onto your radar image.
So why not do it accurately? Having the radar picture overlaid on a
chart solves a lot of mysteries. Is that target the buoy marking Parker
Reef, or is it someone fishing for salmon near Parker Reef?
The trick as I see it is to be able to tailor the chart underlay (or
overlay) so that you can control the amount of data displayed on the
screen. This to me is the big advantage of vector charts over raster
charts (I think I've got that right). As I understand it, a raster
chart is just an electronic picture of a chart. A vector chart has the
same information, but it's been layered rather than everything being in
the one "picture." So with a vector chart like the C-Map NT system we
have on our boat, you can turn off whatever layer(s) you don't want to
see at the time. You can turn off depths, bottom contour lines, place
names, bottom description, land details, etc., etc., etc.
The ability to do this means that you can superimpose the radar picture
over the positional picture without there being so much information on
the screen that you can't make sense of the radar picture. We do this a
fair amount even though our equipment does not permit the combining of
the radar picture and the plotter picture. There are times when we want
to see all the information on the chart, and times when we want to
simplify the display to just the basic information of route, water and
land outlines, and navaids.
The reliability issue is one to be considered, as it is nice to have a
backup if the primary system(s) fail. I use computers enough at work
for complex operations to personally not want to trust my navigation to
one at this point. It's not that I don't trust the navigation
software-- I don't trust the ability of a consumer computer to work
indefinitely without crashing, locking up, or entering any of its other
1,327 failure modes.
Consumer computer operating systems are getting better (usually) with
each new version, and eventually they'll reach a point of being
something that can be truly counted on. (You don't need to tell me that
you've been running Windows XYZ 24/7/365 and never had crash, because
for every one of you that tells me that I can walk around in my building
and find someone who will say that Windows XYZ has done everything to
them but burn their house down.)
But if we were in a position to install a new nav system on our boat
today, if there is a dedicated system that overlays radar and chart
plotter functions from reputable manufacturers like Furuno, etc., we
would be inclined to go that route. Yes, they are computers too, as is
our now-old-fashioned Echotec plotter. But they're not trying to do
navigation functions while also trying to keep the acrobatic act that is
Microsoft Windows from falling off the high-wire. I believe the
reliability of dedicated system-- the Furunos, Raymarines, etc.-- is
such these days that the odds of a failure are pretty remote. I would
definitely want a backup to the plotter system, either a second GPS
unit, a handheld plotter, a Loran, etc. And of course, when it all goes
to hell and the batteries fall out of the boat, there are the paper
charts and the compass.
The radar I personally don't view as quite so critical, although I know
there are people who will vehemently disagree with me. Perhaps this is
because in the 1980s and early '90s we did a lot of boating (fishing) in
the fog in Puget Sound in a boat with no radar (but with a Loran and
charts). Don't get me wrong-- I'm not advocating not using a radar if
you have one-- we certainly do. But if it went blink and died, as long
as we knew where we were and where we were going route-wise, it would
not be the end of the world.
As I said, I'm used to aviation, where displays combining radar and
positioning information have been around for a couple of decades now.
Granted, the radar so far tends to be wx radar, but the value of putting
the two together is obvious as soon as you see the display. A perhaps
better example is the ground control radar most airport towers have
these days, which paint real-time images of everything that's stationary
or moving on the airport (except people) on top of a graphic
reproduction of the airport. This is the display supported by the round
antenna you'll see spinning real fast on top of a control tower. If all
they saw on this display were the targets, the system would be of little
value.
______________________________
C. Marin Faure
GB36-403 "La Perouse"
Bellingham, Washington
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