Re: [Paddlewise] GPS Errors Summary

PeterO wrote:

> Three questions if you have time. i) What is GPSD compared with GPS 

Differential GPS uses a second signal from a land based reference to
correct for some of the errors in the signal. It makes a very accurate
system much more accurate.

The WAAS system is another version of the same idea.

> Is
> it possible to determine longitude without a time reference (Greenwich)
> using celestial navigation. 

Yes it is possible but not easy.
The lunar distance method was mentioned and has been used by a few
people. Joshua Slocum was one who used lunar distance, he had a clock
but it
had no minute or second hands.  :-) At least so goes the legends.


> With your measurements on the trimaran is
> the sextant gimballed in any way to help with stability or is that a
> ludicrous concept?

The only boat I know of that used a mounted sextant is a submarine. They
have the sextant function built into the periscope.
On a trimaran the boat rolls so much less than a monohull that it is
far easier to get a good sight and it is faster so that a navigator
might
shoot three rounds of stars in the time it would take to do one round on
a mono.
The better accuracy of each sight and the greater number of them to show 
you when one of them is not good you can be much more certain of the
fix.

In general, on a ocean crossing you don't need to be very accurate at
all.
You only need to be good enough to be sure of not missing the
destination
land mass. In many cases this can be pretty rough.

Most navigators make it a matter of pride to refine their ability to
produce an accurate fix and make a landfall at a desired spot at a 
predicted time.


> By the way I still have a problem using the word pilotage or piloting for
> finding ones way along the coast in a kayak. My friends in the Australian
> Navy tell me its a bit inappropriate considering the sophistication and
> skill required to bring a modern large ship into harbour. Is the phrase
> "coastal navigation" generally considered an acceptable alternative these
> days?

Yes, today most people, especially in the small boat world (rather than
ships)
would call it coastal navigation.

Just to note a "Pilot" is also a term used to refer to a book of
information
used to navigate and operate a vessel in a particular part of the world.
Much information is gathered together and kept for reference, some of it
dates
back centuries.  These books make interesting reading.

 
> All the best, PeterO

Thanks,
I'm rambling again so will stop here.

michael
***************************************************************************
PaddleWise Paddling Mailing List - Any opinions or suggestions expressed
here are solely those of the writer(s). You must assume the entire
responsibility for reliance upon them. All postings copyright the author.
Submissions:     PaddleWise_at_PaddleWise.net
Subscriptions:   PaddleWise-request_at_PaddleWise.net
Website:         http://www.paddlewise.net/
***************************************************************************