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Subject: Re: leg 56 results/problems
From: Dan Hogan (dhhogan@XXX.XXX)
Date: Sat Jul 24 1999 - 18:37:44 EDT
>Here are my results from Leg 56.
>
>1. not computed
>
>2. 124 T, 1480 nm to Cape Horn from 1150 Z DR.
OK
>3. Mar 23 1848 ZT DR = 5049 S 8027 W.
A tad off, but what are you using for Sailings calculation?
>Q1 and Q2 were worked on a plotting sheet I drew on a piece of typing
>paper, scale 6 nm per mm.
>4. Mar 24 0013 Z fix = 5131 S 8105 W.
OK
>Sight reduction by HO 211. Regulus was the unknown body observed at
>00:14:30 Z. Identification by 2102-D star finder, described in
>Bowditch. Confirmed by Regulus LOP matching other LOPs.
Yes
>Other unknown body probably Miaplacidus. Did not reduce this sight,
>as the angle of cut with the other LOPs would have been poor and I
>felt an additional LOP not worth the bother.
Yes
>LOPs were plotted on a 3 mi/mm plotting sheet centered at 50 S 83 W.
>This allowed the DR, fix, and Cape Horn to fit on one piece of typing
>paper.
>
>5. Total compass error = 27 W. Variation 3 W. Not sure why we're
>asked for variation, since it's stated after Q6.
Did you get the revised edition of Leg 56? I had made a gross error in
the initial issue.
>Compass error based on the Regulus bearing vs. predicted bearing at
>the fix position (from HO 211). The Miaplacidus (?) bearing was on a body
>at 66 deg altitude vs. 14 for Regulus, thus I felt it less suitable for
>determining compass error.
Right
>6. 122 T, 580 nm to Cape Horn from 0013 Z fix.
Close, Ok if you are doing it the hard way, without using the Sailings.
>>From same plotting sheet as Q5.
>
>7. Compass course 128.
Hmm check this.
>8. ETA Cape Horn Mar 25 2340 ZT.
OK on date.
>
>Current is 1 kt dead on our stern for practical purposes. Speed/time
>computation via E-6B aviation slide rule.
>
>
>All the above was written before I looked at the answers. It looks
>good except for Q5 and Q7. To determine compass error, I assumed we
>were supposed to compare the compass bearing of a celestial body to
>its computed azimuth. I used Regulus, whose Zn at the fix coordinates was
>49. Compass bearing was 22, so compass error was 27 E, not 27 W as I
>stated. But this still doesn't match the answer, 15 E. How do you get
>that?
>
>Right before Q7 we're told, "Our Var is 3dW". Was this a trick to see if
>we would disregard unreasonable data?
>
>The error in my ETA is due to my distance being 3.5% high. That's
>more than I like, but I suppose it's unavoidable when using a plotting
>sheet for a 550 mi leg at high latitude.
>
Dan Hogan WA6PBY
dhhogan@XXX.XXX
Navigation-L: http://nav.cnchost.com
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