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  NAVIGATION
Monday 10th September 2007 at 3:24:09 AM  

darell
Cruiser
Posts  27     Points   27
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i've just gone through some navigation techniques. i worry that i must be completely missing out on something, since this technique occurred to me:

Picture this:
1. The sky is clear for measurements
2. You have a good quality watch set to GMT

For longitude, is it possible to:
1. Take sun sightings to find the exact local noon, when sun is at it's zenith
2. Find exact timezone difference between position and Greenwich
3. Translate that to degrees to get your longitude

could this work?
 
Monday 10th September 2007 at 3:32:10 AM  

coasttrip
Cruiser
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yes, indeed! it's possible to take sightings to find the exact local noon.

this technique includes sightings before local apparent noon or LAN, then recording the time and the sextant reading (hs).

then you can proceed with the noon sight for latitude as normal. and immediately reset your sextant to the reading taken before LAN, and wait for descent of the sun. in your sextant, it just kisses the horizon you recorded the exact time.

and to give you the exact time of the sun's crossing on the meridian, you then add the two twice and divide by two again.

After that, search for the sun's GHA in an almanac for the time you calculated and that is your longitude.

plain and efficient. If you do it carefully, you can reach the few miles of your longitude, which is good enough for a ships sailing on high seas.
 
Monday 10th September 2007 at 3:49:44 AM  

fly_guy
Cruiser
Posts  21     Points   21
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There's this really good book called Longitude, that goes through the process and politics of developing a reliable method on how to compute longitude as you sail. try to research on that.
 
Wednesday 19th August 2009 at 3:43:09 AM  

smartcom
Dinghy Sailor
Posts  2     Points   2
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For books on this and other aspects of astro navigation, with reviews, have a look at http://www.winastro.com/winastrobooks.html
 
Wednesday 4th November 2009 at 8:35:35 PM  

ralph.bufi
Site Employee
Posts  167     Points   167
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Halu sailors,

      Thanks for sharing a nice sailing techniques..

Happy sailing.....



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