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Old 23-01-2013, 11:40   #16
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Re: SExtant Newbie?

I think everything has been said here. I'd just point out that there seems to be many many sailors who have boats with sextants aboard who also don't know how to use them. If you want to buy one just put an add at the marina and I'll bet someone will want to sell you theirs. The sextant isn't the only thing you'll need though. You'll also need the Nautical Almanac and a couple other tables depending on using 229 or 249. They are an expense as well. Then there is the learning part and practice.

I've become lazy too and turn on the GPS when I want to know where I am. I could use the sextant but don't and I do a few practice shots each year even though the Nautical Almanacs are $36 a year. It is a hobby and a dying art. There will be fewer and fewer sailors in the future using celestial navigation which is a real shame but many many sailors too don't know how to splice line or know what a deadeye is so its just another thing that is lost to modernization.

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Old 23-01-2013, 12:16   #17
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Re: SExtant Newbie?

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A sextant is an archaic navigational instrument; courses in its use were abandoned by the US Naval Academy back in the previous millenium.
I am not current on this issue, but I believe that courses on sight reduction were abandoned in favor of electronic sight reduction. Last I heard actual use was still taught. So the USN has not abandoned celestial navigation, just modified its practice to suit current technology. They understand that in the event of a major war with Russia or China the GPS constellation will be one of the first things to go.
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Old 23-01-2013, 12:32   #18
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Re: SExtant Newbie?

If you want to do this it can be cheap, or easy but not both.

Easy is a good sextant, HO-249 Volumes 2&3, Mary Blewitt's (sp?) howto book, a couple of watches and a new almanac every year. Figure $1000.

Cheap is $160, which gets you 1/2 or 1/3 the accuracy, you can only shoot the sun and stars, and there is about 50% more lookups and figuring to get the results. But the almanac is good until 2050, it is only 30-40 pages long and includes the sight reduction table. See this post of mine for more details: Poll-Blue water. Is a Sextant Necessary?

For a backup system, cheap and small are the way to go.

Here's a decent site: http://www.titulosnauticos.net/astro/index.htm
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Old 23-01-2013, 12:39   #19
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Re: SExtant Newbie?

Actually all you need is the nautical almanac, Nories tables, a Timex watch and a plastic sextant. No need for sight reduction tables. Less than $300, all brand new.
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Old 23-01-2013, 12:42   #20
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Re: SExtant Newbie?

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Originally Posted by Adelie View Post
I am not current on this issue, but I believe that courses on sight reduction were abandoned in favor of electronic sight reduction. Last I heard actual use was still taught. So the USN has not abandoned celestial navigation, just modified its practice to suit current technology. They understand that in the event of a major war with Russia or China the GPS constellation will be one of the first things to go.
If it's being taught, it's being taught as an elective. The required course on celestial navigation was dropped in 1998 by the US Naval Academy. The reason cited, when the announcement was made, was that celestial navigation could only determine position accurate to within three nautical miles. That's on a ship, of course. It's extremely difficult to achieve such accuracy on a small boat.
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Old 23-01-2013, 12:59   #21
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Re: SExtant Newbie?

navigating by the sun and stars is not easy. as a matter of fact it used to be a military secret just two hundred years ago. celestrial navigation is an all day task. morning sun, noon time sun, afternoon sun, evening stars and constant DR. and plotting. the best military navigators using sextants are happy to get a correct DR within 5 Miles. to reduce one sextant sight will take 15 minutes under good condition. try it with the boat rock and rolling, try it in poor weather. try it in days when you cannot see the horizon or even trying to find a star. you may go for days on DR only. your plotting had be pretty damn good. I'v done all the above and I use only GPS now, the sextant is home on the shelf. I never even mentioned the accuracy of the time, A whole chapter there. this can go on for hours. spherical trig. Marc St Helaire method, Norries Tables, air navigation tables, nautical Almanac .upper limb, lower limb, height of eye. I got my yachtmaster offshore after 6 months learning celestrial. nothing easy about it. and that was before GPS. the last time used my sextant was when Venus was in front of the sun a few months ago and I used the sunfilters to view this. that was fun.
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Old 23-01-2013, 13:21   #22
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Re: SExtant Newbie?

Whether you need a sextant or not will depend on the kind of sailing you are going to do.

Electronics may and will fail. Sextants may and will fail. Good to have both aids, if so dictated by the voyage.

And if you do need one, then you are better off knowing how to use it.

It is not difficult.

I would not buy a toy sextant, nor an an antique collectable. A plain quality sextant will be equally good for learning and for actual use.

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Old 23-01-2013, 13:21   #23
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Re: SExtant Newbie?

Newbie. First of all, it isn't as hard as everybody makes it out to be; in fact it is fun to learn and to do. You will need, as mentioned above, a sextant. The Davis plastic sextants are fine and good enough to find your way to anywhere in the world. They aren't quite as precise as a good quality micrometer drum sextant but they are plenty good for ordinary navigation. You will need an almanac and tables. You can download HO249 from <http://msi.nga.mil/NGAPortal/MSI.portal?_nfpb=true&_pageLabel=msi_portal_page_6 2&pubCode=0012> for free. For that matter you can download Bowditch for free if you have a couple of spare hours. Get all three volumes of HO 249. Volumes 2 and 3 are fine for Sun and Moon sights which are the easiest. Volume 1 is different. You will understand it better when you have gotten a little experience but it is a terrific help for star sights if you ever want to try them. You will want some VPOS Plotting sheets to plot your LOPs on. You can download them for free from <http://www.efalk.org/Navigation/plot1.html>. For an instruction book you can't beat Mary Blewitt's little book "Celestial Navigation for Yachtsmen" $9.95 on Amazon. The only math you will need is adding and subtracting. A little geometry won't hurt. My advice is to forget "Noon" sights and treat every sight by the same sight reduction process. That way you will be able to do Sun, Star, Moon and Planet sights at any time you can get them during the day. By the way I have done many a Moon sight at night. A moon half full or better illuminates the horizon just enough. If you want to go on and increase your investment get an Astra IIIB from Celestaire at <http://www.celestaire.com/> for about $660. Have fun
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Old 23-01-2013, 14:04   #24
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Re: SExtant Newbie?

Hi all again

Thanks for lots of good advice. The sextant to be used only in a situation if all else fails. As pointed out it is a connection to the art of sailing and it would certainly give me an insight to the original sailors navigation skills. I will definatly have 3 or more different electronic GPS devices with maps.However a sextant will be part of my gear. Oh yes thanks for the links I will do a little more reseach tonight .

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Old 23-01-2013, 14:33   #25
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Re: SExtant Newbie?

I would say NO on the plastic sextant for learning. The reason is, the inherent inaccuracy of the plastic instrument can mask small errors in sight reduction and in taking the actual sight. As a backup, for someone already well versed in celestial navigation who is on a strict budget, okay I give it a cautious half thumb up. For learning, you need to KNOW that you have a reasonably accurate instrument, so the error is all you. In like regard, I must caution against a used sextant. A limb could be slightly warped and you could zero out the index error but still be a couple of minutes off at a high angle, or even several minutes off. Again, for a backup, a verrrrry inexpensive used sextant of presumably good quality (plath, frieberger, tamaya, etc) would be a reasonable option for a budget constrained sailor. For learning, go with a new one.

Now a new metal sextant is gonna cost you some big bucks. UNLESS you go for the Chinese Astra IIIb. www.celestaire.com is your friend. Probably around $500 now. I bought mine back when they were $275. This is an ideal learner sextant, nearly as accurate as a top of the line Plath, but waaaaay cheaper. The box is pretty cheesy but you can get a Pelican case for it if you don't mind that it doesn't look very nautical.

GPS? That will be your primary position-fixing method. It is easy. Fast. Convenient. Accurate. Celestial is none of the above. It has class, and you get an elitist rush out of it, maybe, but the main advantage of celestial tools and skills is that it is still useful in a post-apocalyptic absence of GPS satellites, or the system crashes due to some North Korean cyber attack, or you get hit by lightning and all your electronics are fried, or you lose the ability to charge yoru batteries. Celestial has potential even when forced into low-tech mode. BUT... as a low tech backup, it MUST be TOTALLY independant of electronics or electricity. So, while it is cool to whip out a scientific calculator and having memorized the formulae, refer to the almanac for ephemerical data and reduce your sight, or even more cool to just plug your Hs into a computer program or an iphone or droid app, you ought to instead go with the classic method that uses HO 229, which is the sight reduction tables, and the Nautical Almanac, paper, and pencil. And your plotting tools. Even if you have no chart, you can, if you know how, construct a mercator plotting sheet and plot your LOPs on that, advancing as needed for a fix. No electricity? No problem. You wil never know within feet where you are, but in the middle of the ocean if you can determine your position to within a mile, you are good to go. In pilotage waters, you can determine your position by ranges, crossed bearings and special cases, and other visual aids. Again, low tech. Anyway, your celestial skill set and tool set MUST include a non-electrified method of sight reduction.

Even before you buy a sextant, you can practice the MOST BASIC form of low tech navigation... DR, Dead Reckoning. The Dead actually probably is derived from DEDUCED reckoning, but who's counting. Anyway, at some point in the voyage, presumably the beginning, you know precisely where you are at. If you know you went at x speed in x direction for x time, then you have a pretty good idea where you are at then, too. And Y more hours later, at Y course and Y speed, then Z hours more, and you should be able to make a fairly accurate determination of your position. The more accurate you can judge your speed, (no electronic wizardry, or it isn't low tech) and the direction that the boat actually moves, which can easily be 20 degrees from the direction the boat is pointing, and the more careful you are about recording your observations and putting them on the chart, the more accurate your DR position will be. The ultimate low tech speed indicator is a chip log. This is simply a piece of wood, typically triangular or pie shaped, with the sharp corner weighted so it just floats, and a long piece of string. Now, at 1 knot, if you deploy your chip log, and let the string run for a timed hour, 6060 additional feet of string will pass over yoru transom. Not very practical. Especially when it is time to pull it all back in. Divide that figure by 60 and at one knot, 101 feet of string will pass over your stern. Still not very practical, is it? Okay then... 1/10 of a minute, 6 seconds, should see 10 feet of string pay out. Ahhh... that's more like it. Not quite as accurate but very handy. So you make a knot in the string where the chip is being dragged about a boat length back, then make another knot at 10.1 feet and another at 20.2 feet, and so forth. At 50.5 feet, the 6th knot, you are looking at a speed of... 5 knots. Careful timing and taking the average of several tries will give you a speed quite accurate enough for a DR. Your course through the water you can determine by hand bearing compass, sighting back down your wake. Unless you are running downwind, you are going to be making some leeway, so your compass heading is not good enough. Plotting the distance and the speed for your hour's run gives you a DR position. You can further refine this into an Estimated Position by plotting the set and drift of the current from the DR, for the same hour, since sighting down your wake gave you only the course through the water, not course over ground. It is possibly more convenient to simply do all this with arithmetic and only plot the Noon DR... up to you. But keeping a proper DR is the essence of navigation. Compare your DR position every noon with your GPS, and you will eventually find your DR getting quite accurate, sometimes within a couple of miles. Your DR position goes hand in hand with celestial navigation. You have to start with an assumed position, when using the azimuth/intercept method, and this assumed position will be based on your DR. In other words, you have to know where you are, in order to figure out where you are at LOL!

More stuff on DR and celestial, and in fact all facets of navigation, in American Practical Navigator, also known as Bowditch, or Pub no.9. Get it. It is your Bible.

And BTW, another additional backup that could be good to have, is a small hand-held GPS, even an iphone or other smartphone with internal GPS. If you only turn it on once a day to get a fix and then turn it right back off, the battery ought to last quite a few days. This daily electronic fix would be a wonderful add-on to your DR. In fact, the thing to do in such a situation is to begin your DR plot anew, from the daily fresh electronic fix.

Last but not least, in order to reduce a celestial observation to an LOP, you have to have an accurate time reference. A battery powered portable SW reciever will work for that. Tune in to WWV or WWVH at 5, 10, or 15MHz for the time ticks, and either set your watch or clock by the time ticks, or note the difference between the official time and your watch or clock. Knowing this difference and recording it will allow you to calculate the rate by which the clock gains or loses, so in the absence of a time signal, you can still calculate the correction. You should know the time of a shot to within the nearest second. You don't need a fancy chronometer but you do need a timepiece that gains or loses at a predictable rate, and you need some way to check your time by a coast station, or even by the top of the hour time tick from the BBC. A Timex or Casio wristwatch is good enough, especially one that is kept by your navigation station instead of on your wrist.
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Old 24-01-2013, 13:10   #26
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Re: SExtant Newbie?

In my opinion if you think celestial navigation is easy then you must be doing it wrong!
Davis plastic sextants do work. Many folks, including myself, have crossed the oceans with them. They are much cheaper and if used properly can give you as accurate a fix as you need to make passages. Your sextant will be stored in a locker for most of its life anyway so don't spend a lot of money on a fancy one. Again, that's just my opinion. Celestial Navigation by H. O. 249 by John E. Milligan is my favorite guide.
If you have lots of money go for the expensive ones and take a celestial navigation course if you can find one.
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Old 24-01-2013, 13:43   #27
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Re: SExtant Newbie?

Quote:
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Were you looking for the "Talk Like a Pirate" forum?

"Avast" is a command meaning to cease and desist. It has never been a form of greeting.

A "foray" is an attack or incursion. "Blue yonder" is a aeronautical idiom for the sky. It does not in any way connote oceans. Sailors do not take boats into the wild blue yonder. And sailors tend not to like getting their feet wet.

A sextant is an archaic navigational instrument; courses in its use were abandoned by the US Naval Academy back in the previous millenium. Claiming you want to learn to use one because you don't trust electronic gadgets is like going into battle with a sword because you don't trust guns.

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Old 24-01-2013, 14:33   #28
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Re: SExtant Newbie?

I find great irony in the fact that I use my GPS clock when taking sights
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Old 24-01-2013, 15:30   #29
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Re: SExtant Newbie?

It never fails to amuse me when accuracy is advanced as the clincher for using a second GPS as sole backup for a GPS.

Because, quite often, the same person will (if pushed to acknowledge a certain degree of risk inseparable from having 'all eggs in one basket')

then turn around and say:

< <What's the big deal if you do get some sort of multiple failure ?:

It's not rocket science:you just sail west (or whatever) until you see land then turn right (or whatever) > >

I'm not sure why pinpoint accuracy is so essential to the first proposition,
when the second proposition flings it out the window.
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Old 24-01-2013, 15:36   #30
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Re: SExtant Newbie?

BTW , to the OP

(who seems to be dealing nicely with any attempts to bash his proposal ;-) )

I don't think there's any point in striving for pinpoint accuracy if you see a sextant as an adjunct and backup to GPS

There are simplified methods which are fine for such contingencies, including one in the guff you get when you buy a Davis, which includes a perpetual almanac, IIRC.

Unless you make a habit of sailing through the 'Dangerous Archipelago' (Tuamotu) or some such (very unusual) waters.


So, plastic IMO is a good way to go.
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