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Old 04-06-2006, 18:11   #1
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Celestial Navigation

Aloha All,
A couple of months back a sailing friend of mine asked if I was up on my celestial navigation skills. He wanted to know if I could teach him what he needed to know to find his way around. I foolishly said, "Yes."
I realized too late that it had been 22 years since using sextant and tables to cross the ocean. I was committed to helping him and it really is a lucky thing that his high school in Peru was very thorough and taught him mathematics far better than my high school in Oregon because he remembered more about solving some problems than I did.
He is a visual sort of learner and I am about 50% visual and 50% something else which I have never figured out.
To make a long story a bit shorter, our very first eperimental sight was a noon sight where we sat on the rocks of the shoreline here in Paradise Park on Kaloli Point where we could have a North meridian passage noon sight. We got down to the Point a bit late and while I was fiddling with filters and couldn't find the sun he got it and we started ticking off sights up and over for altitude observations. That was day one.
A few days later we met to work out the computations to give us latitude and longitude. His first sextant experience ever gave us sextant altitude for latitude that placed us within 2 and 3/4 miles from where we were actually sitting on a rock. That is the "best I've ever seen." (an expression I've learned from being a U. S. Sailing Instructor) Our time check along the way was a bit uncoordinated but we came within 6 miles of longitude. (Time of sights is very important and should include seconds)
On these high islands I would count that as a direct hit for a first time sextant user and please don't give any credit to me as a teacher because he is a great student. Our next experiment is going to be finding latitude using Polaris after we do a few more noon sights.
I am coming up with a really good noon sight form that anyone can use with a Nautical Almanac to find latitude and longitude. Let me know if you are interested and I'll make it available to forum members.
Kind Regards, --John--
Book Recommendation - Celestial Navigation by H. O. 249 - John E. Milligan
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Old 05-06-2006, 03:01   #2
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You are re-inventing the wheel! - lots have done exactly the same and created their own forms (even me) Mine are designed to remind me exactly where to find the information!
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Old 05-06-2006, 11:26   #3
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Thanks Talbot. You must be right about reinventing the wheel because I'm doing exactly what you did by adding information about where to find things in the Nautical Almanac. I think what I should have said was I'm coming up with a revision to a current form which makes it easier for me. I shouldn't have said "really good form" because that is rather subjective. I'll still offer it for anyone who wants to try it.
Kind Regards, --John--
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Old 05-06-2006, 11:55   #4
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if you pm me your email address, I will send you back my versions plus a decent plotting sheet.
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Old 07-06-2006, 18:19   #5
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I would like to see this... been attempting to make celestial stuff make sense.
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Old 07-06-2006, 22:56   #6
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Aloha Zach,
Mark "Talbot" has the best forms I've ever seen. If you talk really nice to him maybe he'll forward his to you. I can help with explanations if you'd like and I do recommend you get the book that I recommended in my first post. It is one of the simplest and easiest to understand that I've seen. Kind Regards, --John--
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Old 08-06-2006, 08:47   #7
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Hey John.

What would you say "might" be the hardest part on learning about taking the readings, on celestrial navigation?

I have not learned anything about that yet. And I was just wondering what might be the hardest thing to learn about it?

Nothing against electronics. But, I am sorta against all the techno babbled gadgets. And in the marine environment. They could fail anywhere, anytime. And I could be in somepart of the world. When some gadget might fail.

I like to keep things simple. Sextant and paper charts. With a GPS onboard.
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Old 08-06-2006, 10:37   #8
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IMHO the easiest bit is the paperwork, i.e. taking the information from the sextant and accurate watch and translating that into a position line. After all that is mere maths.

The hardest to get right is the actual sight itself, i.e. getting used to operating the sextant and getting accurate readings. This is a skill that needs considerable practice from a small deck, and is still beyond some people.

provided you are content with sun/run/sun and mer pass then that is all you need.

Personally I prefer to take star sights cause you get an accurate position immediately, but this requires identification of the stars. Best way of doing this is with a star globe. Some of these astronomical programmes provide the same info, but no good if there is a power failure. There is a way round this, by use of the air tables vol 1 and pre-determining where the best stars will be, then going on deck with the sextant set to the correct altitude, and searching on the correct bearing, and hoping those particular stars are not obscured by clouds!
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Old 08-06-2006, 11:36   #9
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I must agree with "Talbot" but with one caveat. You cannot miscalculate and get an accurate line of position so practicing your calculations is very important.
Practice with the sextant is like practicing with archery or small arms except with star sights your target is pinpoint and you are on a moving deck plus you have to record your shot to the second. Practice, practice, practice.
An analogy - If you can calculate your own income taxes then you certainly can do the calculations required for celestial navigation. Different types of sights, i. e. meridian passage, sun, planet, moon, stars require different calculations so like doing your taxes you must choose the proper form.
I suggest learning celestial using air navigation H.O. 249 using the book I recommended in my first post. "Talbot" has the best forms I've ever seen so it would be good to talk with him really nice.
Regards, --JohnL--
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Old 08-06-2006, 16:45   #10
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"plus you have to record your shot to the second"
I added a sports wrist watch to the handle of my sextant to use as a timer for sighting. (OK, I stole the idea.) Anyway it does make it a little easier for me.
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Old 08-06-2006, 17:10   #11
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Agree with all the above. Back in the days when a sextant was the only choice and I was using it daily, 1/4 to 1/2 mile circle of position wasn't unusual in good conditions.
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Old 08-06-2006, 18:38   #12
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Aloha Dana,
You must be really good!! I always considered 1 mile a really good shot and thought I was lucky to do any better.

Pura,
That's a great idea no matter where you got it and I'll always consider that I learned it from you.
Regards, --John--
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Old 08-06-2006, 18:52   #13
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As I said, in PERFECT conditions and back when I was doing them every day. Must admit I was sinfully proud of sailing through the Tuamotus at night on a star sight and David Lewis" book.
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Old 11-06-2006, 16:46   #14
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Sextant - AstraIIIb
I have a secondhand sextant that has one of those little battery compartments in the handle where there is a place for two AA batteries. I suppose it is there to provide power for a small light for your sights at dusk or dawn like the old Davis I used to have.
The previous owner left the batteries in to corrode and destroyed one of the terminals and the switch fell apart. Oh well?
Is this worth fixing or should I just not worry about it? I really never used the light on the old Davis that much but it might be a nice feature. Anyone out there with a bunch of experience willing to share on this subject? Regards, -- JohnL--
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Old 11-06-2006, 18:03   #15
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John-
Fixing the battery corrosion might be easier than you think. If you can, remove the battery compartment, or the entire handle. Strip it down if you can. Once you have it as accesible as you can, swab plain white vinegar into the corroded parts. Soak them in it if you can, even better, and then use q-tips or a toothbrush to scrub those parts of any remaining crud.
It usually comes off in one or two passes. The vinegar should not hurt any metals, plastics, or the optics in the sextant.

Once it is clean, rinse with fresh water and dry before re-assembling. If you can get a fiberglass or brass "contact cleaning pen" (Micro-Tools sells them on the web) that's also a good one to have. Looks like a thick felt tipped pen--expect the tip is strands of fiberglass or metal, so you can get into odd places and wire brush them.

Once it is dry, I'd suggest a dab of silicone grease (aka brake grease or light bulb grease or high vacuum grease) on all the contacts. Vaseline will work, but that migrates and the silicon grease doesn't. Either one will ensure the contacts stay good, even if the next batteries leak on them.

FWIW, I avoid Duracells like the plague. Seems like as soon as they hit the "use by" date? They leak. Eveready's lithium cells, a bit pricey but available at Radio Shack and other places, might be a good idea since they have a 10-year shelf life at "only" twice the price of alkalines. You're buying a stronger package, too.

The switch...might be harder to replace, but the odds are you can fit SOME kind of push button switch in to replace it.<G>
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