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Old 31-07-2009, 16:11   #1
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Artificial Horizon

It's been a very long time since I used my Sextant...pre GPS. However, I've dusted it off and started to fondle it once again. Since S/V Semper Fi still sits in the yard as I fit it out, I can't dash off shore and use my sextant.

I recall the artificial horizon works on a reflected basis and that you half the reading to determine the HS of the body. Is there a current sextant user who knows if I could simply use a pan of water to achieve the reflection and be able to once again become familiar with my sextant while still at home.

Glen
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Old 31-07-2009, 16:51   #2
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Artificial horizons

Yes, a dark bowl will be a little easier to use because of the contrast. Place it somewhere the wind does not ripple the surface and where neither the subway nor passing trucks disturb the horizon. Or use old engine oil.

Rocking the sextant to the right and left a little may well give you images that part and come together again: like the sun coming down to kiss the horizon when you do that at sea. The least angle that matches the images together will be what you want. 5 minutes practice often repeated makes perfect. An hour will just make your wrist ache.

Getting the sun, moon or star to come down to match the image reflected in the bowl:~ Fix the zero error (below) if it is more than a degree or so, then: 1) Double the angle above the horizon calculated from the almanac, or 2) Look straight at the sun with the sextant at 0º, then swing the arm to begin bringing the image down towards the bowl. Follow it. Count slowly to ten and try again... not often enough to get frustrated...

1/2 the angle. No need to subtract half the diameter of the sun or moon. But do point the sextant directly at the sun or moon, starting at 0º, and match the images together carefully to read the zero error.

Other adjustments we can go into next month: so sit back and enjoy your favourite beverage.
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Old 31-07-2009, 17:43   #3
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George,

Many thanks.
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Old 03-08-2009, 08:47   #4
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You may find that floating some mineral oil on the service of the water will help with ripples if you have that problem. You can save and re-use the water/oil mixture in a cast of bleach jug or the like.

FWIW...
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Old 03-08-2009, 09:33   #5
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What are you focusing the sextant on in the bowl though? Is it the reflection of the sun?
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Old 03-08-2009, 15:39   #6
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Choices

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Originally Posted by unbusted67 View Post
What are you focusing the sextant on in the bowl though? Is it the reflection of the sun?
If it is a sailor's bowl there will be choices of mermaids, sirens... Sun, Moon or a bright star.
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Old 04-08-2009, 00:43   #7
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The bowl serves as an artificial horizon through the reflection of the object on the liquid surface. For $30 or so bucks you can buy an artificial horizon, but as George refreshed my memory a bowl works just fine.

You will have to make some adjustment to the angle read on the sextant, but if you want to practice a bit, without going to sea, this is a great way to do it.

I truly appreciate all of the responses that I've received. It has been many years since I took a sight with a sextant so I thought I'd ask the question and see if I could sit on my High Desert Patio and try to brush away the cobwebb that have grown on both the sextant and my brain housing group.

Again, thanks to all!
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Old 04-08-2009, 02:26   #8
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Some of those artificial horizons may fit your sextant so that you can take sights in low fog and at night when the horizon is indistinct or invisible: as long as it is not too lively from boat motion. Then they are worth the $30.
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