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Old 21-06-2024, 16:12   #1
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Lewis Navigation on Simple Longitude

Simple longitude
The basic fact is that taking a evening sight of a star on almost exactly your latitude and nearly overhead reduces the need to determine a navigational triangle! Only a small percentage correction is needed from your observed distance. If time says a stars longitude is at a distance of 1000 miles West of your assumed position, and the difference in latitude is only several degrees, the increase in distance is less than ten miles. 11 ˝ deg +25m 17 ˝ deg=50m 25 deg =100m ((about))
So its counter intuitive, but you Subtract ten miles from your sextant obs to get distance between longitudes of the star and your longitude…
YOU can also get your longitude during your noon sight. You time your first sight, at say 51Degrees 10 minutes eight seconds. You figure your noon sight, then set your sextant at the 51 degrees & etc. When you once again touch the horizon with that value, you note the time. The time halfway between both sights gives your longitude within a dozzen miles or so!
Also see the "lifeboat navigation"" section in Bowditch for a simpler Polaris method. Or I can post it here later. Most teachers enjoy making navigation far too complicated! ... Enjoy, Lewis
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Old 21-06-2024, 18:37   #2
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Re: Lewis Navigation on Simple Longitude

Interesting bits of information, I would love to try the trick with Sun.

I have usually ignored celestial bodies that were almost overhead, because it took a relatively long time to take the sight.

I found it easier to shoot multiple stars and planets that were at lower altitude, even in the tropics.

My sights were taken from the bridge of a 15000 tonner, unafected by 8 foot waves. I imgine it would be difficult to measure the altitude of a body close to t zenith on a deck of a 36 foot sailboat in similar sea conditions.
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Old 21-06-2024, 19:17   #3
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Re: Lewis Navigation on Simple Longitude

bringing the sun or star down to the horizon is the same art no matter how large an angle. its just about practice. On a yacht you just brace yourself against something and wait till you are on the crest of a wave to kiss the horizon. and your horizon is lots closer with lhe lower heighth of eye.. Which affects accuracy. But people did all that for centuries. My Coast Guard ships were only 180ft and 255ft long and yes they did lots of movement. Think four years winter North Atlantic. You might try taking a sight using a pan of oil for a horizon! It actually works, yes its in Bowditch. you merely cut the HO in half with no heighth of eye corr.
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