I agree Kinch. If I were operating in the more modern pre-GPS days,
I'd be inclined to use Celestial until I hit the coastal charts with the LORAN
lattices overlaid on them and start using LORAN (ground waves) with Celestial
checks. When I got close enough (20 nm or so) I'd start looking for
conspicuous radar targets and finally go to visual bearings and radar ranges as
I made true landfall. Is this about right?
The wonderful thing in my mind about modern navigational convinces is that
we can be very confident that we are where our electronics tell us we are.
This allows us to quantify the effects that were only known generally in the
past e.g., set and drift. I can actually watch set and drift occur on my
ECDIS screen as each position marker is laid down. It amazes me how much
the ship can be pushed off course in a matter of hours. We now correct for
this periodically so we stay quite close to track at all times.
When I last made landfall in September of 2009, we were arriving in
Wilmington, NC. Our last sighting of land was Ascension island, many days
before. We navigated by GPS and my Celestial observations which were in
agreement. I was on watch when we first made radar contact. The
coast is not well contoured, so I was looking at the buoy placement for the
channel for confirmation. There was a lighthouse which was identified
by light characteristic and bearings were begun at about 17 nm (it was about 5
AM local). I also started taking radar ranges as I could find them and
crossing them with visual bearings. Of course the ECDIS and other GPS
receivers were plotted as well. I found, not surprisingly, that the visual
bearings and GPS crossed nicely, but the ranges were off due to the nature of
the coastline and I tended to disregard them. I even tried a range off of
a known buoy which was slightly better than land, although obviously a low
quality LOP due to the fact that it was floating Navaid.
The point is that i did what every navigator should do in these
circumstances, I used every available means to obtain a position so that i could
safely navigate the ship to the pilot station.
Jeremy
In a message dated 12/14/2010 4:03:40 P.M. Central Asia Standard Tim,
Kinch@Telefonica.net writes:
Very well put Jeremy and perhaps some more people sitting at their desks
will realise that navigation is about much much more than the Maths – a point
I raised myself in an earlier post. (Perhaps my gaff about the bad horizon
under that star to the Northeast just went over the heads of those who only
look out their South facing windows!).
In another post you stated “On the other hand, sailors made landfall by
these graphical methods for years without problems, so perhaps I am being a
bit pernickety.” I believe you might be – we did just fine without
programmable calculators or GPS confirmation of our position. And (although
again shot down by the purists), I still believe that a mile or three made no
difference whatsoever. Celestial navigation was for ocean passages. After
three weeks crossing the Pacific from Panama to Japan, you would be a very
imprudent mariner indeed if you navigated in close to coastal dangers without
first having established your vessel position by means other than by Sun, Moon
or stars .....a position that may be many hours old, leaving the vessel
subject to varying effects of winds and tides in the interim period.
Kinch.
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