On Sun, 16 Sep 2007 22:00:26 -0400, Red wrote:

brucepaige wrote:
How come all the advocates of a relative low tech method of
determining a position never mention that the system is unusable for
navigation in tight spaces, narrow channels, etc. and dead reckoning
or taking sights or measuring depth will be necessary.

I never hear anyone recommend having a lead line on board in case your
electronic depth sounder fails or a chip log mounted on the stern
pulpit in case your electronic speed log fails.

I see a number of arguments in this discussion. Fist, GPS recievers,
like all electronics are prone to occasional errors and failures. There
are numerous stories that abound in cruiser's logs on the net of GPS
readings that reported the boat to be a half mile or so inland, or in
the middle of a channel but the boat hits a charted reef, etc. There
are perhaps hundreds or maybe thousands of places around the world that
have innacurate GPS coordinates or innacurate maps used for the GPS
data. The Garmin chartplotter on the boat I usually sail on shows us on
land when we are in the middle of the channel in home port (and yes, the
settings are correct for the charts). So other forms of measurement are
always appropriate to know. And like it or not, the Pentagon did shut
down the satellite system for one day, and can do that anytime again,
not to mention the likelyhood of the system having problems as the
satellites age. And since I both sail and work on boats I can tell you
that both the depth sounders and speed logs do fail with amazing regularity.
Red

Yes, electronic devices fail and sextants get dropped knocking the
mirrors out of alignment.

Yes some GPS positions show you as on dry land when you look at a
chart and a "cocked hat" sextant fix a mile on a side is doing really
good, i.e., you are somewhere inside a half a square mile area.

You can't use celestial navigation to stay in the middle of a narrow
channel because you can't take shots and work the calculations fast
enough, even with a calculator.

The original poster asked " Should I learn celestial navigation before
doing circumnavigation ?" and to me the answer is a resounding NO!

If you want to learn an archaic skill such as sword fighting, shooting
the long bow, or shooting stars then more power to you but the ability
to do celestial navigation is not a necessary skill in today's world.

In closing let me say that I learned celestial navigation from a Lt.
Colonel, the Lead Navigator in a SAC B-52 squadron and used to carry a
sextant, H.O. tables and expensive watch and all that, but that was
fifty years ago. Things have changed.



Bruce in Bangkok
(brucepaigeATgmailDOTcom)