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Peter

P F wrote:

'What this coastal nav course proposed was taking the
same three  
corrected bearings but plotting from the fix position
onto clear  
material from a point on the plastic sheet
representing the side  
opposite to the land � the seaward side. So three 
position lines  
radiating outwards.'

I left it a week, but no-one else has jumped in.

Regardless of the tool used for the plotting, such as
'clear sheet', a station pointer, or a Douglas
Protractor, what has been suggested to you in that
technique is downright dangerous. There are two
reasons for this.

From three LOPs gained from the hand bearing compass,
suitably corrected, plotted normally, you produce on
the plot a cocked hat which warns by its size if one
of the LOPS is inaccurate. If you use the horizontal
sextant angle station pointer type method of plotting
that same data, it does not indicate any error, it
just generates an apparently ambiguity free dot on the
plot which is almost certainly wrong.

Furthermore, the horizontal sextant angle station
pointer type method itself is notorious for a poor
angle of cut built into its geometry, particularly if
the 'middle' object sighted is further away than the
two 'side' objects sighted.

Don't be tempted by what you've been told - a tidy
plot is not the same thing as an useful plot.

Michael Bradley




        
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