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Old 05-12-2014, 18:12   #16
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Re: Easy to Use Sextant

A plastic Davis will work well enough. If you want metal, go for an Astra IIIB. Nice unit for the price.
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Old 05-12-2014, 18:48   #17
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Re: Easy to Use Sextant

" If you're relying on a computer/tablet/smart phone/whatever to do the math,"
You miss the point, which I was fairly explicit about. The software does not REPLACE doing the math, it serves as a check and balance to see if your math is right.


One day a friend said "let's do some sights and get some practice" and after they shot the sight, while they were doing the math, I shot a sight, reduced it on a Palm, and came up with an answer that was some 900 miles closer to our position.


Obviously [sic] my friend made a simple math error. But with a reduction program to do a fast check, I was able to eliminate the source of errors.


If you drop a GPS, or the sextant, you are SOL. If you drop the PDA, no big deal, you can always go back to doing it the paper way. And old fashioned celestial calculators (or PDAs) run for months worth of simple work on cheap batteries, without an external infrastructure like satellite constellations to create vulnerabilities. In the event of a massive solar flare, the GPS system might (might) go offline. The PDA? Too damn to know or care about that.


If it works, it works. If it doesn't, you open the book. Can't say the same thing about the GPS or the sextant themselves. Point clear about that now?
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Old 05-12-2014, 19:39   #18
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Re: Easy to Use Sextant

I too would have a s/h plastic for learning. Then I would keep it as a spare and buy a metal one for navigation.

We have a DDR built alloy sextant. Inexpensive, accurate. I would buy one again.

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Old 05-12-2014, 20:52   #19
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Re: Easy to Use Sextant

buy "SELF-TAUGHT NAVIGATION" by r. kittredge. it is about 80 pages. here is a short quote on sextant use, from page ix ,,,"forever impressing the quarterdeck by every means at hand with the wonder, the difficulty, the intricate magic of navigation," try to find a community college that teaches it, or buy a cheap used plastic learner for about $50, and DON"T look at the sun. fish and geese can migrate, so I know you can figure it out<.>
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Old 05-12-2014, 20:57   #20
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Re: Easy to Use Sextant

Times sure have changed I learned by the bowdege its a complex looking situation but to be honest find someone that already knows and have them walk you through it . There are dozens of methods but you will need to find the method that suites you . I agree with the work sheet.As far as a sextant I had the pleasure to learn with a old in the wooden box 10 pounder OK maybe it wasn't that heavy but man was it on sight I later bought a m15 plastic and you no once I learned the arc it was just as good.. ..........
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Old 05-12-2014, 22:34   #21
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Re: Easy to Use Sextant

About 60 years ago I took a CN course as part of the requirement to attain a Mates ticket in Canada. Plastic sextants were very new and I picked up a Davis for about $10 brand new! Our first practice session was a noon site from a beach in Vancouver with our instructor, a set of reduction tables which we shared with other classmates and the simple steps and math formula which we had dutifully learned in class.
I'll never forget fiddling with the filter for the sunshot as someone counted down the chronometer time. Got it nailed on the first try, ran the numbers and proud as hell discovered I was standing in a corn field about 60 miles north of Calgary, Alberta!
Very humbling and got better with practice but never forgot the experience! Phil
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Old 05-12-2014, 23:50   #22
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Re: Easy to Use Sextant

One thing which comes in handy is an artificial horizon attachment. It screws into place, & provides you with a level reference in lieu of the sea. Thus you can practice taking sights even if you're stuck in Iowa.


Bravo, BTW, for learning a dying art. It's a handy skill to have, not to mention fun. Albeit doing the reductions by hand can be frustrating, as a mistake on line 5 may not become apparent until 10 minutes & a page & a half of calculations later.


Both in terms of taking the sights themselves, & doing the math. When you're learning it, do the process(es) the same way every time. As it'll greatly lessen your chance for making a goof.


Also, as soon as you've taken your shots, tuck the sextant safely away into it's case/drawer. Like immediately, just as you would do with a sheath knife. It'll cut down on the risk of dropping or bumping it, well that habit, plus the neck lanyard which you make for it... just in case.
Do this prior, to starting your calculations.
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Old 16-12-2014, 16:45   #23
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Re: Easy to Use Sextant

I've had a Davis Mk 15 and then upgraded to an Astra III-B. There's no comparison between the 2. The III-B is really a fine instrument which will take a lot of the frustration out of taking a sight.

If you're practicing on land, an artificial horizon is necessary. The Davis AH (artificial horizon) is ok but you can make your own from a dish containing old Diesel oil or just water. For best results you have to protect the liquid from being disturbed by any breeze. But! I've made many good sights using a puddle with the wind blowing and super-imposing the Sun directly in the middle of the shimmering reflection of the Sun from the puddle.

Sight reduction is the more complex part. As others have suggested, develop a method of your own using the basic principles of CelNav. Also, William F. Buckley made a video called (I think) Celestial Navigation made Simple. I watched the video (before Youtube removed it) and learned how to do Sun sight reductions using his method (HO 249 & Nautical Almanac). Yahoo, somewhere, has his entire worksheet and related Nautical Almanac and HO 249 pages available.

CelNav is made even more difficult as those inclined toward it (sort of) are very good at math, can't explain it or make it simple and have no personality.

The Stars are easy to shoot and reduce but are more difficult than the Sun. The Moon is pretty easy too.

Like so many things, the complexity of CelNav and related sight reduction are reduced by knowing what to do and where to get the information.

I've found that it's easiest to do a sight reduction using paper, pencil and no computers (but sometimes using a calculator). Believe me...I'm no math whiz at all! However, if you want a good Sun sight reduction program the best I've found is at BackBearing.com in the form of an Excel spreadsheet. It's simple, easy and quick.

If you have any questions....just ask or PM me.


Hope that helps.
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Old 16-12-2014, 17:11   #24
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Re: Easy to Use Sextant

Quote:
Originally Posted by PDA1 View Post
I've had a Davis Mk 15 and then upgraded to an Astra III-B. There's no comparison between the 2. The III-B is really a fine instrument which will take a lot of the frustration out of taking a sight.

If you're practicing on land, an artificial horizon is necessary. The Davis AH (artificial horizon) is ok but you can make your own from a dish containing old Diesel oil or just water. For best results you have to protect the liquid from being disturbed by any breeze. But! I've made many good sights using a puddle with the wind blowing and super-imposing the Sun directly in the middle of the shimmering reflection of the Sun from the puddle.

Sight reduction is the more complex part. As others have suggested, develop a method of your own using the basic principles of CelNav. Also, William F. Buckley made a video called (I think) Celestial Navigation made Simple. I watched the video (before Youtube removed it) and learned how to do Sun sight reductions using his method (HO 249 & Nautical Almanac). Yahoo, somewhere, has his entire worksheet and related Nautical Almanac and HO 249 pages available.

CelNav is made even more difficult as those inclined toward it (sort of) are very good at math, can't explain it or make it simple and have no personality.

The Stars are easy to shoot and reduce but are more difficult than the Sun. The Moon is pretty easy too.

Like so many things, the complexity of CelNav and related sight reduction are reduced by knowing what to do and where to get the information.

I've found that it's easiest to do a sight reduction using paper, pencil and no computers (but sometimes using a calculator). Believe me...I'm no math whiz at all! However, if you want a good Sun sight reduction program the best I've found is at BackBearing.com in the form of an Excel spreadsheet. It's simple, easy and quick.

If you have any questions....just ask or PM me.


Hope that helps.
As I recall, the WF Buckley video you mentioned above is available for free viewing IF one is a member of the Amazon Prime service (for streaming videos). It has been years since I watched that video (I rented it years ago) but the cover caught my eye while I was looking at the selection of available videos on Prime.

___________

On another point, I bought the Astra IIIB and shot sights (side by side with an expert using his sextant) and got comparable to his much more expensive sextant. So I suspect at a certain point, the differences in sextants accuracy in practical USE becomes more one of individual technique in taking the sights and then accuracy in calculations. In other words, I feel an Astra IIIB is a good and suitable instrument for yachtsmen.

The advice to start with a plastic one for classes is good advice too. Not many people progress past the class, so a small investment up front is smart.
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Old 16-12-2014, 17:16   #25
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Re: Easy to Use Sextant

...the days when mariners used to go from ship to ship with their sextants in their mahogany boxes are gone...

Whenever I'm going on someone else's boat, I would amongst other things, always take my Garmin handheld GPS; does that not count?
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Old 16-12-2014, 17:45   #26
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Re: Easy to Use Sextant

Quote:
Originally Posted by bobnlesley View Post
...the days when mariners used to go from ship to ship with their sextants in their mahogany boxes are gone...

Whenever I'm going on someone else's boat, I would amongst other things, always take my Garmin handheld GPS; does that not count?
The quote is from my earlier post. Perhaps it needs explaining. When we paid off one vessel and went to join another we usually traveled by air as the next vessel was seldom in the same port. The sextant was always part of our carry on luggage. All ships had ship's sextants but deck officers always had their own. The ship's sextant was usually used by cadets/apprentices who were poorly paid and could not afford a sextant.
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Old 16-12-2014, 17:53   #27
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Re: Easy to Use Sextant

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Originally Posted by bobnlesley View Post
...the days when mariners used to go from ship to ship with their sextants in their mahogany boxes are gone...

Whenever I'm going on someone else's boat, I would amongst other things, always take my Garmin handheld GPS; does that not count?
Yes, of course it does and you're so right. Both instruments are tools and mariners of old would probably have only dreamed of having such accuracy of the GPS.

Sextant work is extremely interesting and is closely related to working with charts and practical, acute, observation. GPS provides much more precision and ease of use but doesn't seem to provide much harmony between sailing and the world about and above us.

GPS however, is susceptible to the whims of those that control the signals. Sextant work can't be jammed, is undetectable and requires no power. But, the weather can make things a little bit difficult!

It's fun!
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