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Subject: Leg 67 - I give up!
From: Paul Hirose (71202.2014@XXX.XXX)
Date: Thu Jul 20 2000 - 02:47:51 EDT
After wasting far too much time today on Leg 67, I'm giving up. Have
not been able to solve the celestial fix. The problem is that only the
zone time of the shots is given. Not having worked any of the recent
Silicon Sea legs, I don't have the dead reckoning longitude necessary
to convert zone time to UT.
From the wording of the problem, I inferred that sailing 614 mi on
course 290 would take us toward Barbados, but we wouldn't be there
yet. So, with a small scale chart, I backed up 700 mi from Barbados on
the reciprocal course, and took that as the assumed position for my
sight reduction. My LOPs showed the guess was far off, but they did
cluster well enough for me get an improved assumed position. With that
and a larger-scale chart I re-reduced the sights. Unfortunately, the
first two sights I reduced still had big intercepts. At that point I
called it quits. No doubt some blunders on my part have not helped; I
haven't done celestial in a long time.
It seems to me you could assume ANY time zone offset from Greenwich
and get the star LOPs to cross at a fix. Unfortunately, each time zone
would give a different fix! But if the moon shot is good, it ought to
resolve the ambiguity. Since the moon moves 1/2 degree per hour with
respect to the stars, try different longitudes (hence time zone
offsets) until the moon LOP falls on the star LOPs. That requires more
computation than I'm willing to perform with hand work and tables.
I'm interested to see if someone can show a NON-ELECTRONIC solution to
the Leg 67 fix. With a computer it's so easy to play trial-and-error
with the AP that it's not nearly as challenging.
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