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Old 21-12-2008, 10:45   #16
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David has a good point. You can go with an inexpensive model for now and upgrade if you feel it necessary at a later time. Most people have GPS which will give you very precise data, but a sextant can be fun and is a useful back up tool. I suppose how much you want to spend depends on how much you will use it. If it is only going to be used intermittently, then go with a nice certified one. I rather like the Davis Mk 25, which runs a bit less than the Chinese made Astra. I use it rather more than my C. Plath.
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Old 26-12-2008, 17:25   #17
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Blackjack:

Having read through your questions and some of the replies, the following thoughts come to mind.

1. The Davis Mark 15, a plastic sextant is inexpensive, I bought mine on Ebay, and it came with a level device that eliminates the need to "rock" the sextant, total cost including shipping was $110 as I recall. One thing about this plastic sextant, possibly others too, take a look at EBERKS sextants, English made is the following. Index errors can be really wild, featuring significant changes from one day to the next. Of course, you can adjust to compensate or simply apply mathematical corrections, the problem being that the index error is not consistent. You don't have to put down a whole lot of money though.
2. I also have an Astra 111B with conventional mirror, split image a opposed to whole horizon. Their price has gone up a bit, I paid $510 a year ago, they list in Celestaire catalog for about $600 at present. They seem like a quite good instrument, certainly entirely adequate for practical navigational use. Being Aluminum framed, they do not weigh a ton either.

Also on Ebay and other places too, one finds these surplus Russian sextants. I'm told that they are quite good optically mechanically too. They appear similar to Freiberger sextants, which are made in what used to be East Germany. Two things about buying these Rusian sextants. One is payment. The sellers all want payment by wire transfer, which banks charge a fee for, and if there should be problems, it could be tough getting a refund. Also, many of these Russian sextants come with two telescopes, usually one, possibly both of them producing an inverted image, which re "shooting" a celestial body, sun, moon, stars and or planets is a problem. Shipping adds about $100 to the cost of the sextant too.

As to myself, strange though it might be, I'm strictly a "landbased" navigator, I'm not a boating type. For reasons I myself do not understand, I got interested in celestial navigation. If nothing else, it's an interesting intellectual exercise, and then there are it's practical applications, such as finding out where the hell one might be. By the way, this works pretty much the same way on land as it does at sea, except that on land, away from the sea shore or large lake, one uses an artificial horizon of one type or another.

For an interesting presentation on Celestial Navigation, you might take a look at the following web site: afewgoodboats.com . It's currently listed as "under construction" meaning that the sites owner is doing something with it. Try it when you get a chance. Sorry to have gone on at such length.
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Old 26-12-2008, 19:32   #18
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Aloha Blackjack,
I don't know if you are still in the thinking stages of this endeavor but I will try again to make the point that you don't need a high priced metal sextant to learn and take good sights. All you need is a Davis Mark 15 at about $75. They will do the job just as well as the high priced metal ones and will be a great sextant.
You will learn if you want to do celestial navigation or not with a less expensive investment.
The most silly argument I've heard on this forum is how to keep time for celestial shots. Some said to use your GPS to get a good time. If you have GPS that works you don't need to do all the sights and celestial calculations. Very silly argument.
But, that's why this forum is so good. It makes you do some serious thinking.
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Old 26-12-2008, 19:42   #19
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Aloha Blackjack,
I don't know if you are still in the thinking stages of this endeavor but I will try again to make the point that you don't need a high priced metal sextant to learn and take good sights. All you need is a Davis Mark 15 at about $75. They will do the job just as well as the high priced metal ones and will be a great sextant.
You will learn if you want to do celestial navigation or not with a less expensive investment.
The most silly argument I've heard on this forum is how to keep time for celestial shots. Some said to use your GPS to get a good time. If you have GPS that works you don't need to do all the sights and celestial calculations. Very silly argument.
But, that's why this forum is so good. It makes you do some serious thinking.
regards,
JohnL
Keeping your watch to GPS time makes sense if GPS ever goes down. At least you would have a better idea of your longitude than if you never checked your watch against GPS time. That's why ships to this day keep chronometers on board and check them against a radio source....either GPS or WWV or some other source.
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Old 26-12-2008, 23:57   #20
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I thank you folks very much. I think I'm going to go with the Mark 25. Maybe a little better than someone learning needs but I dont want to have to buy another one later.
Ive found what appears to be a fairly good deal on a learners kit over at Landfalls which can be upgraded to include a Mark 25 sextant.
Beginner's Celestial Navigation Kit
Thanks again for the valuable information. I'll be sure to let you all know how I'm doing.
Take Care
Craig
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Old 27-12-2008, 11:16   #21
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I used a Mark 25 to cross from Hawaii to the mainland in the early 80s. A very good choice. Congratulations.
Kind regards,
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Old 27-12-2008, 15:15   #22
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I thank you folks very much. I think I'm going to go with the Mark 25. Maybe a little better than someone learning needs but I dont want to have to buy another one later.
Ive found what appears to be a fairly good deal on a learners kit over at Landfalls which can be upgraded to include a Mark 25 sextant.
Beginner's Celestial Navigation Kit
Thanks again for the valuable information. I'll be sure to let you all know how I'm doing.
Take Care
Craig
Blackjack:

Looks like a pretty good kit. As for the latest Nautical Almanac, they are a yearly thing, you could save close to 50% by going with the Commercial Edition, same data, soft covered, with a few pages at beginning and or end of ads, that you can tear out or ignore. Suit yourself.

The Davis Mark 15, as I recall, is pretty much the same as the Mark 25, except for color, illumination, not needed for sun shots or daylight moon shots (Mk 25 has it, Mk. 15 doesn't) and horizon mirror, Mk. 15 is "traditional, that is split image"Mk. 25 is "whole horizon" which some say is easier to use. I don't know.

If you like, I could probably send you, via e-mail, copies of USPS sight reduction and plotting sheets that you could print out. I suspect that the forms Landfall provides might be the VP-OS a form that covers a larger area, usually 2 Degrees Latitude x 4 Degrees Longitude. The USPS forms cover 1 Degree Lat x 1 Degree Long.

You might also consider joining USPS (United States Power Squadron), see if there is a squadron in your area. They offer seminars open to the public and courses in piloting and celestial navigation, among other matters, for members. Also, the Coast Guard Aux. might be worth contacting, depending on your location.

Best of luck learning.
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Old 27-12-2008, 20:17   #23
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The "reproduction" you were looking at is not a sextant. It is an objet d'art. It costs less than the Davis Mark 25 plastic sextant Celestaire, Inc.: Marine Sextants : Davis
which has been discontinued, but can be found used at many stores and net sites. In classes at the Naval Academy, students achieved the same accuracy with this instrument as those who were using far more expensive ones. The key word here is 'student' as opposed to daily users.
There aren't a lot of daily users anymore.
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Old 28-12-2008, 11:03   #24
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The "reproduction" you were looking at is not a sextant. It is an objet d'art. It costs less than the Davis Mark 25 plastic sextant Celestaire, Inc.: Marine Sextants : Davis
which has been discontinued, but can be found used at many stores and net sites. In classes at the Naval Academy, students achieved the same accuracy with this instrument as those who were using far more expensive ones. The key word here is 'student' as opposed to daily users.
There aren't a lot of daily users anymore.
A couple of points re comment from Sandy, things that sort of pop into mind.

1. An interested individual can most certainly learn celestial navigation with an inexpensive plastic sextant. Plaths are, I'm sure, lovely instruments, however for a beginner?
2. Electronic navigation (GPS, Loran and whatever else might come along) are certainly more accurate (is the increased accuracy needed) and they are faster also, however "old fashioned celestial navigation" seems a hard learned, classical skill and as such strikes me as worth maintaining, if at all possible.
3. Sandy mentions, at the close of his post, the following, re the discontinuation of the Davis Sextant, which strikes me as interesting. "In classes at the Naval Academy, students achieved the same accuracy with this instrument as those who were using far more expensive ones. The key word here is 'student' as opposed to daily users.
There aren't a lot of daily users anymore."

Re the lack or "daily users", that seems just a bit sad. Of course, celestial navigation, as I practice it, is purely an academic/intellectual exercise, so some might discard my opinions. That is, of course, up to them.
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Old 28-12-2008, 13:01   #25
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The eBay Ross sextant auction is for a dust catcher and nothing more. Save your money for something worthwhile.

The Davis Mk15, 20, and 25, as well as the EBBCO, to name two good lines of plastic sextants, can deliver reliable measurements, certainly from the deck of a small boat. Forget the Davis Mk III; its real value is only as an inexpensive demonstration tool.

However, all of these sextants have barely adequate optics. A sight is quite literally that: seeing the object being shot (usually the sun, but not always) dropped to the horizon. With the narrow field of view provided by these sextants, the job of dropping the object to the horizon becomes frustratingly difficult. If the sight or shot is defective, all is lost, literally.

The simple fact is a good sextant isn't cheap. You're paying for good optics, sound engineering in the index arm bearing, flat, accurately mounted mirrors and a precise, accurate arc and screw. Additionally, a good sextant has enough filters for both the index and horizon to make seeing the horizon easy while dropping a safely filtered image of the sun.

Celestaire's Astra IIIB is good value for money spent and Ken Gebhart's customer support is excellent. Do it right the first time, and you'll acquire a skill that will stand you in good stead. Take the cheap route, and you'll probably join the ranks of those who gave up celestial navigation as being "to hard for me!"

DISCLAIMER: I have no connection with EBBCO (now defunct), and I am a customer with eBay, Davis, and Celestaire. I have no other connection with any of these companies.

Added: Sight reduction is, with a good work sheet or calculator program, little more than cookbook work. Plug the numbers into the receipe and an LOP pops out of the oven. The part that needs practice is the actual sight. It's a physical process that takes some skill to master and, importantly, takes practice to retain the skills. In short, practice, practice, practice, even if there's a GPS-driven chart plotter on board. We are, after all, just a battery failure away from the Age of Sail.
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Old 01-01-2009, 19:05   #26
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Below is an ebay listing for an Astra IIIB. The price just now is about $250. This is the kind of instrument you should be looking for. Plastic is okay but if you have the money why not have a work of art aboard?

eBay Motors: Astra IIIB Marine Sextant NEVER USED NEVER ON BOARD (item 300283565909 end time Jan-04-09 20:06:08 PST)
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Old 01-01-2009, 21:03   #27
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Sadly, it's silly season on eBay's Astra auctions (three currently running) with reserves on two of them and the third starts at a relatively high price. Oh, yeah, and one guy is selling off an Astra he got for free as a business Christmas present (he got it for free, you get to pay $300+ - what's up with that???). Too bad you missed the Freiburg sextant that went for about $310 only a couple of days ago. This sextant was made in (the now former) East Germany and is an excellent sextant (don't own one, have used one on a trip to Bermuda). Anyway, time for a little patience and waiting for the right deal to come along (also helps to have a good eBay sniping tool to nail down a really good price).
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Old 01-01-2009, 22:40   #28
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Thanks for the heads-up and the link Sam, I'm going to keep an eye on that one. I hate those 'reserve' auctions though.
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Old 01-01-2009, 23:18   #29
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Sextant

Buying a sextant off ebay is frought with difficulties because you have no means of checking the inherent errors before you buy. The sextant you have shown has a small diameter telescope lens which, if the unit is a real sextant, would make use on a yacht very tricky. On a yacht you need a wide angle telescope, and most modern sextants come with one. The older sextants sometimes come with two telescopes - one wide and one narrow. It also shows a magnifying lens over the mcrometer which is unusual - they are usually only used on a vernier sextant. Before you buy learn or get someone to show you how to check the basic errors - I.E, parallax etc - its not difficult. Then you should be able to pick up a relatively cheap Plath or equivalent second hand and having checked the basics yourself, and buy with confidence. The sextant would come with a certificate mounted in the box which will show you the manufacturing errors - they all have them to a greater or lesser extent. The plastic sextants are good learning tools but are sometimes more difficult to use as they are very light and difficult to hold steady. Equally once you have acquired the skill you will probably be dissatisfied with the accuracy levels. Taking the sight with a sextant is the easy bit - learning the calculations that you need to manipulate the information is what takes the time and if you get to that point, it can be frustrating to find the first and starting figure you use - the altitude from the sextant is not so good. If you are not too concerned about understanding the calculations - there are calculators and software programs available which will process the data for you. But remember junk in produces junk out.
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Old 01-01-2009, 23:40   #30
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Horizontal Sextant Angles

One of the most usefel funtions for a sextant on a boat is horizontal sextant angles. Most people on yachts seem unaware of this. If your other equipment has failed or you only have a hand bearing compass you can use the sextant to take a horizontal bearing between two known points and you have an instant position. More than one set of angles is obviously better. In an anchorage set up your sextant with a horizontal angle between two points and if it changes - you are dragging. Equally you can take a vertical angle off a point of land - mountain or radio mast and you instantly have a distance available either from a set of tables or using some elementary geometry. On our boat the sextant is used for these functions (especially a quick check on the anchor) probably a lot more than it is used for sun or star sights.
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