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» Online Classroom   »   » Public Discussion of Cel Nav   » d Value corrections using HO 229

Author Topic: d Value corrections using HO 229
Bill Brucato

 - posted February 11, 2004 11:38 AM      Profile for Bill Brucato           Edit/Delete Post 
David, In using HO229 for sight reduction I see that the d value found with Hc can sometimes be -60.
Now, the interpolation tables in HO229 go to 59.9 and no further. How do you treat a -60 d value correction?
Does this mean that no correction to Hc is required? Or have I missed something.

From: Celestial Navigation Home/Online
Bill Brucato

 - posted February 17, 2004 09:14 AM      Profile for Bill Brucato           Edit/Delete Post 
Will these subjects be addressed? I posted this and the other two questions at David's request. My LAN estimates are working out after reviewing the chapter on LAN, but I still need some insight on "second estimates" and the "d" value correction in 229.
I'm also working on latitude by ex-meridian transit (any body) and I don't see how to accomplish this. I'm aware it's not in the course material, but I'm hoping you can help with this.

From: Celestial Navigation Home/Online
David Burch

 - posted February 17, 2004 11:24 PM      Profile for David Burch           Edit/Delete Post 
It would be best to address the issue of d = -60 by giving a specific case: ie give aLat, dec (deg and min), and LHA for the case that you have in mind that gives d=-60. This is obviously a special case, so we need specific examples then we can work it out.

the d in this case is equal to how much the Hc changes if the dec changes by 1 degree. Hence if d = 60 and dec min = 37' then the d corr should be 37'.... but we should look at the specific examples you have, because we can then first compute the solution so we know precisely what the right answer is and then we can check this with the tables.


the second part of the question has to do with "ex-meridian sights," which is an entirely different topic, so i am moving that to a new topic to keep things organized a bit.

Bill, i might add that my understanding was that you were doing an ocean endorsement to a 1600 ton license. to my understanding, that test does not include ex-meridian sights... nevertheless, we will address this in the other topic.

From: Starpath, Seattle, WA
Bill Brucato

 - posted February 18, 2004 09:45 AM      Profile for Bill Brucato           Edit/Delete Post 
David, Thank you very much for your responses to my many questions. I appreciate the fact that "real world" navigation has nothing to do with the exam room and I am grateful you've addressed these problems for me.
I'll be in the last lap of my preparations for the exam soon and I'll be sure to let you know what I do find on the exam.
When I was studying for my original license, my compatriots and I were able to clue each other in on different aspects of the exams and give each other a "heads up" on what to expect since we weren't sitting at the same times. This was long before the question database was online. Way before!
Anyway, thanks again,
Bill Brucato

From: Celestial Navigation Home/Online

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