Sextant

Discussion in 'All Things Boats & Boating' started by SheetWise, May 19, 2011.

  1. michael pierzga
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    michael pierzga Senior Member

    Follow Gonzos advice...Get a plastic Davis...lightweight cheap and accurate. Its my favorite sextant.
     
  2. welder/fitter
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    welder/fitter Senior Member

    Chances are that they'll be using the cheaper lifeboat(practice) sextants, anyway. I've got a Davis MK15 that is as accurate as any, although the higher quality metal sextants would be more durable. As you've found, they want two limbs for those. Maybe a cheap practice sextant, for now, & a big-dollar sextant for graduation?
     
  3. SheetWise
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    SheetWise All Beach -- No Water.

  4. welder/fitter
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    welder/fitter Senior Member

    Well, hopefully it passes muster when professionally tested. If so, serious "WOW" factor!
     
  5. michael pierzga
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    michael pierzga Senior Member

    Seems I not long ago read that they no longer train Midshipman at Annapolis in Celestial Navigation ?

    Regardless of sextant choice , the critical factor when working with the celestial triangle is knowledge and technique. This knowledge is trapped inside books.

    The books that I have carried on small craft my whole life are...

    Self Contained celestial Navigation with HO 208 by John Letcher, Jr.
    The finest book ever written for small craft navigation , Time by lunar distance , Longitude at Noon, Sextant calibration by stars and it uses the HO 208, Driesonstok tables so the book is compact and truly selfcontained. .

    Emergency Navigation, Pathfinding techniques for the prudent and inquisitive mariner by David Burch. The book covers liferaft navigation as well as describing many simple and effective navigation strategies used by seaman of the past, but long forgotten. ie running down latitude.

    We the Navigators....by the legendary Kiwi sailor Dr. Davis Lewis
     
  6. Chuck Losness
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    Chuck Losness Senior Member

    I have a sextant on board and use it occasionally just for practice and for something to do. It's a Russian made sextant that I bought on Ebay years ago. My biggest complaint is that you need to buy the nautical almanac every year which gets expensive and it was a pain in the butt to pull all the numbers and then put them in the correct places, etc., etc. My main reason for the sextant is for an emergency back up in case I lose all my electronics. So using one of the computer programs would not suit my purpose for emergency backup.
    So last winter I started researching the math of celestial navigation (spherical geometry) and discovered with a few simple formulas and a slide rule or simple calculator you don't need all the books. Attached is what I came up with.
     

    Attached Files:

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  7. michael pierzga
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    michael pierzga Senior Member

    Chuck... sight reduction tables last forever...only the almanac needs updating. The complete HO 208 reduction tables are 100 or so pages...less than a paperback and require no sperical trig via calc or slide rule.. HO 229 or 249 air tables take up a whole bookshelf ...learn 208.

    The sextant is a very useful tool for distance off and precise bearings for DR navigation in areas poorly charted or poorly covered by GPS. Distance off tables are included in the book Self Contained celestial Nav.
     
  8. SheetWise
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    SheetWise All Beach -- No Water.

    I agree -- and thank you for the references.

    On the other hand, an historical piece adds some continuity to the process. It's like playing a 150 year old Steinway ... the mystery of where it has been adds to the thrill.
     
  9. SheetWise
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    SheetWise All Beach -- No Water.

    Thanks! There a lot of information in that short document! If that's your work, I'm impressed. That will definitely get passed along (and checked for accuracy) ;)
     
  10. Chuck Losness
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    Chuck Losness Senior Member

    Most of the formulas I found in "Celestial Navigation" by Wm. Bruce Paulk which I don't believe is printed anymore. I made up all of the work sheets myself. For me at least I find plugging a few numbers into a formula to be way easier than pulling arcane information from the Nautical Almanac. When I was a kid we didn't have calculators and used slide rules. So no big deal. My scientific calculator is made by Sharp. Like I said before you don't need any of the sight reduction tables or the Nautical Almanac which is the beauty of using sins and cosines.
     
  11. tom kane
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    tom kane Senior Member

    Does any body check to see that they are using their "Right eye" when they use a sextant. that is you hold your right index finger at arm`s length against a background verticle surface and close each eye at a time. The eye that does not appear to make the finger move right or left is the eye you use to look through the sextant. If you don`t you may be miles off course. People are different.
     
  12. hoytedow
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    hoytedow Carbon Based Life Form

    That would be a little hard for me, with the patch and all.;)
     
  13. troy2000
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    troy2000 Senior Member

    Congratulations to your daughter, Sheetwise. May she do well, and never regret the course she's set herself.
     
  14. SheetWise
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    SheetWise All Beach -- No Water.

    Thank you Troy2000. She's my youngest (by twenty years), with her away I can now start my other plans ;) I expect she'll have many regrets before she gets to the point where she knows it was worth it -- and then she'll have none. Thanks.
     

  15. hoytedow
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    hoytedow Carbon Based Life Form

    How did things go with the sextant? Good news I hope.
     
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