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» Online Classroom   »   » Public Discussion of Cel Nav   » Hawaii by sextant completed...

   
Author Topic: Hawaii by sextant completed...
David Burch


 - posted October 24, 2018 09:59 AM      Profile for David Burch           Edit/Delete Post 
Congratulations Barry on finishing the book and route. We will look into your questions below that we just received. It looks like you have an interesting application of the traverse table. Note that in principle, no two solutions will be identical in that each reader chooses the sights they include for a fix.... but they should all be pretty close. We will look into the question you raised.

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Hi David and Steve,

Some time ago, you were kind enough to address a problem I had with StarPilot, successfully now resolved. Since then, I have spent a very enjoyable last month working through all the exercises in Hawaii by Sextant. Having now completed all these largely with StarPilot (except for the early running fixes which I completed manually just for the practice!), and satisfied myself that nearly all my fixes were extremely close to the given solutions, I was very surprised to find that at the last fix (P27), my answer to P27d was short by about 65km (my calculated range from the last fix to Pailolo = 110NM, bearing 238 deg.; given solution on p36 = 175NM, bearing 237 deg).

When I use StarPilot to calculate the traverse distances (possibly not the best method?) between each fix from departure Lat/Lon (given on p5) to Pailolo Lat/Lon (same page), I find that my DMG is short by about 150km. I have attached a screen shots of these computed numbers as well as all my fixes transferred to Google Earth.

I’m assuming that this may be due to cumulative error over such a long distance, but I am intrigued by how you arrived at the range quoted in answer to 27d (175NM quoted in the answers to Special Problems on p36). If this is the range from the final CelNav fix (P27) and I use the computed Lat/Lon for this position given in the solutions (p35), the rhumb line distance to the Pailolo Channel still falls far short of the given 175NM – what have I missed, David?

Very much enjoyed working patiently through your book, including the post-trip analysis, but I hate leaving behind unturned stones!

Thanks, David,

Barry (Victoria, Australia)


From: Starpath, Seattle, WA
David Burch


 - posted October 24, 2018 04:01 PM      Profile for David Burch           Edit/Delete Post 
Hi Barry,

Steve worked this out and reports the following:

I used the Problem #27 0831 Fix (22° 05.2'N, 155° 01.3'W) and the Position of Pailolo given on page 5 of the HBS book (21° 07'N, 156° 38'W) and went to the SP-PC to determine the Rhumb line distance and bearing and got 107.5 nm @ 237.2° as a result.

It appears to me that the 175 nm mentioned on page 36 for the result for 27d is a typo. The "0" is missing in the book - should read 107.5 nm.

This would be consistent with Barry's answer of 110 as we are not in exactly the same places.

Thanks Barry for pointing this out. We added it to the Errata. https://www.starpath.com/HBS/errata.htm

From: Starpath, Seattle, WA


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