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Re: leg 56 results/problems
From: Dan Hogan
Date: 1999 Jul 24, 18:37 EDT
From: Dan Hogan
Date: 1999 Jul 24, 18:37 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