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Hello,

I am a new member to the list. and I have a couple of what are probably very
elementary questions about H.O. 249.

1) For yacht navigation to bring all of the sight reductions for a fix to a
common time, Is it valid to use "Alternative table 1- Altitude Correction
for Change in the Position of the Observer" which provides corrections for 1
minute of time? This table deals in ground speeds of 50 to 900 knots (which
is a bit fast for your average yacht I will admit). However if you divide
the speeds at the head of the columns and the values extracted from the
table by 100 and then muliply by the number of minutes you are that have
elapsed since the sight time and the fix time it appears to give a
correction to Ho which and the resulting intercept to bring the LOP to the
desired fix time. Is this a valid technique? Can it be used with longer time
intervals to do a running fix where hours may have elapsed between the
sights? If this works, I would rather do this than the additional plotting
to bring the sights to a common time.

2) Doing sight reductions with H.O. 249 Volume 1. Are intercepts calculated
using only H.O. 249 Vol 1 as accurate as those calculated using Vols 1 and 2
(for those bodies which have declinations less than 30 degrees). Somehow it
always feels like a cheat to not have to mess with the declinations of the
bodies. It is however the only way with H.O. 249 to deal with the
navigational stars with declinations of 30 degrees or more (so it must some
validity). Should volume 1 sight reductions be treated with more suspicion
than  Vol 2 & 3 sight reductions.

Thanks in advance for those to reply or even think about these questions.

Eric Haberfellner

   

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