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» Online Classroom   »   » Public Discussion of Cel Nav   » Hawaii by Sextant - assumed positions

   
Author Topic: Hawaii by Sextant - assumed positions
DrBob11


 - posted April 25, 2016 08:32 AM      Profile for DrBob11           Edit/Delete Post 
How are the AP's determined in the book. They don't seem to match up with the DR. I have been taught to place the AP on the nearest latitude line directly in line with the DR.
From: Florida
David Burch


 - posted April 25, 2016 10:18 AM      Profile for David Burch           Edit/Delete Post 
The selection of the AP is discussed in great detail in our textbook Celestial Navigation, along with many extra practice exercises.

In short they should be within 30' of the DR with minutes matching the GHA so as to cancel minutes in the final LHA. Again, we have many pages devoted to this selection in the text, with many examples.

If you have an example that is contrary to that guideline, then please tell us that example and we will look into it.

From: Starpath, Seattle, WA
David Burch


 - posted April 25, 2016 10:23 AM      Profile for David Burch           Edit/Delete Post 
PS... just noticed that you are referring to Hawaii by Sextant!

I apologize.

There are a couple cases in that book when the not best AP was selected. I thought that each one of those had notes addressing that issue and explaining why it might be best to redo it with the optimum AP.

In that book you can check the computed solutions to see any effect that might be in play. These examples were left in that book on purpose to illustrate these points.

But to answer your question, see the above notes on how to choose the optimum value, which remains correct.

Note in passing, that on some USCG exams that ask for Hc, you must choose the optimum AP to get the right answer, even if -- as in most cases -- it will not have much influence on the final fix.

From: Starpath, Seattle, WA
DrBob11


 - posted April 25, 2016 11:52 AM      Profile for DrBob11           Edit/Delete Post 
Thanks David!
From: Florida


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