NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: That darned old cocked hat
From: Jeremy C
Date: 2010 Dec 13, 23:53 EST
As one of those "practical navigators" using a mixture of traditional techniques and modern conveniences, Peter has something written above something that has struck me.
From: Jeremy C
Date: 2010 Dec 13, 23:53 EST
Peter wrote:
The other apparent contradiction is that practical navigators tend to
take a small triangle as an indication of little error, and a large triangle as
an indication of significant error, and for practical purposes this makes
sense. Yet John Karl and his proposal has reminded us that the larger the
triangle the better the chance that it actually contains the fix position, while
if the triangle becomes particularly small the chances of it containing the fix
position, logically, approach zero.
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As one of those "practical navigators" using a mixture of traditional techniques and modern conveniences, Peter has something written above something that has struck me.
Call me simple, but this is a huge argument to avoid using plotting without
augmenting it with statistical analysis. If all you get from visual
or celestial LOP's are small triangles with significant probability of
the actual position being outside, this degrades a "fix" to an estimated
position in my mind. The only way a fix can be achieved is by subjecting
those LOP's to rigorous secondary analysis, something I doubt most
practical navigators do.
In the same bent, considering the accurate fixes I find with my celestial
observations, reduced and analyzed by computer rather than traditionally
plotted, I think that the way to actually use celestial navigation practically
(ie to quickly and accurately fix the position of a vessel) is to use
a computer program that does all of this and finds your MPP statistically from
the given observations rather than trying to find an MPP by guessing from a
jumble of crossing lines like I was taught to do.
On the other hand, sailors made landfall by these graphical methods for
years without problems, so perhaps I am being a bit persnickety.
I will be sure to tell my captain about this issue the next time he wants
all sorts of visual bearings taken to see where he dropped the anchor instead of
looking at the ECDIS.
Jeremy
