Bruce in Alaska wrote:
I would like to add a simple note here.
OTN talks about using Radar and the Mark One Eyeball to get position
fixes while navigating in coastal and inshore waters. Ok, that is common
practice, and has been for MANY years.
Now consider the accuracy of those fixes, as compared with the accuracy
of an Electronic Position Fixing Device.
BG Dang! I gotta find this place you guys are navigating through, that
requires instant position data, within a few inches.....
Mark One Eyeball.... Taking a sight with binocs even over a compass card
will usually get a line within a degree or two, IF the guy is really
good at it or is using one of those old WWII TBT's... Ok, now figure
that your going to have to do that on at least two bearings, and better
yet, three or four. Ok, now you have to go plot those bearings on the
chart using the reverse bearing from the marker you sited on, and then
figuring in the time difference between the bearings, and the speed of
advance, of the vessel, and you don't get a REAL FIX, but an AREA of
FIX that IS "Orders of Magnitude" bigger than the REALTIME GPS Fix.
First off, the "Mark One Eyeball" method of navigation, can be many
things. What you describe above, is just one of them. The accuracy of
that same method can vary, from, exceeding GPS, to useless, but on
average,will be well within the needed parameters to safely navigate an
area under normal conditions.
Needless to say, this method tends to suck in restricted visibility.
With all due respect Bruce, it's obvious from your above that you are
not all that familiar with the method you are discussing.
Radar..... Same thing here, except that your bearing will tend to be
better, depending on the Horozontal Beamwidth of the antenna, and the
distance, and area of the target which the bearing is to. Again, the
AREA of the FIX will be smaller for the radar because the time to get
the bearins, (two or more) will be shorter, but the plotting times and
the speed of advance will be the same. Again the Area of fix will
be "Orders of Magnitude" larger than the REALTIME GPS Fix.
Here, you are using only one of the methods available to you (in fact,
the time consuming one). Sorry Bruce, but like Jim, your radar
navigation needs work, also. Stand beside me under most coastal
navigation areas in Alaska, take a reading on a GPS fix, at the same
time I take a range and bearing via radar ... betcha I beat you plotting
said fix and the only discrepancy between the two positions will revolve
around how sharp my pencil was (unless of course the chart is in error,
in which case my position is more apt to keep us out of trouble).
BTW, forget the "speed of advance" junk .... it's a lame argument at the
speeds we are talking about for most cruisers.... unless, of course,
they've screwed up and gotten too close to a nav hazard, to begin with.
GPS Fix..... even with out WAAS, this should be in the 30 foot centered
circle, and the speed of advance isn't even a problem due to the small
amount of advance in the one second cycle times of GPS Calulations.
The same can be said for LORAN-C with modern day Receivers, that have
builtin Lat/LONG Calculators, especially if the route has been run
before, and Know Anomalies in the TD's are already accounted for.
If, for the most part, your navigation requires you to be within a 30'
centered circle, then I have to question your "route planning". Granted,
there are times when you need precise distance information and you are
navigating in narrow areas such a marina's and harbors where you have to
work between docks, but in those areas, I'll take radar every time,
because it doesn't care if the charted positions are correct.
Now all the above really is mostly not a GIANT Issue at 7 - 12 Knots,
as there is always enough time to figure this all out. However, I defy
anyone to show me how anything but a Very GOOD GPS Based Navigation
System can be used on a Fast Ferry doing 35+ Knots inside Boston Harbour.
Speed KILLS, and the faster these guys go, the faster one of them is
going to run the rest of us over, because the navigator isn't watching
where he is going, because he is busy PLOTTING his position.
Explain to me why this isn't a problem......
Sorry, haven't ridden any fast ferries in Boston. Rode the ones from
Hyannis to Nantucket. From what I saw, most "general" navigation was
done by "eyeball" and "radar"..... Why?....For those running a familiar
route, it's faster and generally, more "spatial awareness" accurate for
the operator. When a chart plotter is available, it's a fantastic third
tool that frequently changes ranking in importance over the radar and
eyeball..... so, in answer to your question, it IS a problem that
various operators need address, though a simple GPS without a chart
plotter is NOT the solution.
otn
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