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Thread: Sextants

  1. #1
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    Default Sextants

    What are people's preferred sextants, and why?

    I'm pipe-dreaming about upgrading from my plastic Davis sextant. The Tamayas with the larger telescope look good to me, but I've never used one, so for all I know they're duds.

    Alex

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    Default Re: Sextants

    Astra IIIB. Great for the price, I really like mine. Used on ebay.
    Chuck Hancock

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    Default Re: Sextants

    I had a Zeiss, the salesman in Gibraltar let me pick through the stock, to find the one with the least error, as indicated on the correction card.

    I sold it years ago

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    Default Re: Sextants

    I'd recommend one with the full width mirrors; they are much easier to use. And get one with an alloy frame.
    IMAGINES VEL NON FUERINT

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    Default Re: Sextants

    I have my Dad's He was First Mate on a Merchant Marines Liberty Ship in WWII. Torpedoed in the White Sea on a Murmansk run, he carried his sextant when he was transferred to a rescue ship. Needless to say, it means a lot to me. I tried to use it once. No way is my hand steady enough.

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    Default Re: Sextants

    Anybody have any recommendations on how to learn to use a sextant? I learn well from books if there are any that stand out.

    Do they have to be re-calibrated or anything? I don't want to buy one that is not reasonably accurate.

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    Default Re: Sextants

    Mine was similar to a Tamiyah. I preferred it over more expensive instruments. Plath were a little heavy, and of course the plastic...Davis are too light, and difficult to hold steady. Best get one with a monocular rather than a simple lens. The monocular gathers light more efficiently and is easier in twilight. Also the slightly stronger magnification is better for putting the ' lim' on the horizon...sun and moon...

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    Default Re: Sextants

    Quote Originally Posted by J.Madison View Post
    Anybody have any recommendations on how to learn to use a sextant? I learn well from books if there are any that stand out.

    Do they have to be re-calibrated or anything? I don't want to buy one that is not reasonably accurate.
    There are many good books that have been written on the subject. Unfortunately, most are out of print these days but probably easily enough sourced through Amazon. You'll need an "artificial horizon" to practice ashore. Otherwise, you'll have to go out on the water far enough to find a horizon beneath whatever you are shooting. Davis sells a cheap artificial horizon. https://www.westmarine.com/buy/davis...iABEgL9k_D_BwE I don't think anybody ever made an expensive one. You might also want to get a Rude Star Finder. https://www.google.com/search?source....0.5FvTDslrHVs There are also many star finder apps for iPhone.

    As for repairs, you have a few choices, but sextant and magnetic compass repair guys are getting rather hard to find these days. I'd guess there's probably less than a dozen doing it for a living in the US anymore. They are sort of like buggy whip makers. Google them up.
    Last edited by Bob Cleek; 09-06-2017 at 04:17 PM.

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    Default Re: Sextants

    Quote Originally Posted by J.Madison View Post
    Anybody have any recommendations on how to learn to use a sextant?
    I liked the video put out by William F. Buckley. Not sure if it is available anymore. I know some people have a problem with him for political reasons, and may be distracted by those feelings, but he avoids politics in the video. Not everyone's cup of tea, but he taught me how to use a sextant and then make use of the sights, a skill I have since allowed to lapse.

    For books, I recommend Learn to Navigate: By the Tutorial System Developed at Harvard by Charles A Whitney (available on Amazon), a relatively easy to understand text for a sometimes difficult subject. The book covers both coastal and celestial.

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    Default Re: Sextants

    My dad always preferred the Bendex Bubble Sextant.

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    Default Re: Sextants

    [QUOTE=J.Madison;5337393]Anybody have any recommendations on how to learn to use a sextant? I learn well from books if there are any that stand out.

    If you contact your local CG Auxilliary they most likely offer a class on the subject.

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    Default Re: Sextants

    Many organizations will offer classes, depending on where you live. A class A sextant is more accurate than a class B but a good class B is plenty accurate for anything we'll be doing. Remember, astronav is for offshore. If you're accurate enough to within 5nm, you're close enough. If you're close enough to land according to your recconning that you're worried, you should be paying attention to switching from astro to pilotage. The sextant will put you within 20 miles of land, from there, make your visual landfall and come in with decent visibility using traditional pilotage and coastal navigation skills by taking bearings of landmarks etc. If you can get accurate within 5 nm, you're not doing too badly on your sextant use.
    There are 6 errors built into a sextant. 3 are correctable, 3 are permanent errors. It's been over 15 years since I've had anything to do with a sextant but the three correctable errors are relatively easy to spot and adjust for. The permanent errors are simply a known error in that particular instrument and is accounted for in the calculations after you shoot your celestial body.
    Another use for a sextant is to take horizontal sextant angles. The angle between two land based targets can be plotted to help you determine your position. Bowditch has a good chapter on sextant use. Otherwise, amazon should have plenty of tutorial type books on it. Good luck Mr. Madison. You'll need one with that beautiful craft of yours.
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    Default Re: Sextants

    Astra IIIB. Great for the price, I really like mine. Used on ebay.
    Cool. I've got a search running now, just to see what turns up.

    had a Zeiss...
    Seeing "Zeiss" makes me cringe at what one must cost today, but I'll have a look around.

    I'd recommend one with the full width mirrors; they are much easier to use. And get one with an alloy frame.
    I've heard good things about the full windth mirrors, but never played with one. Not questioning your preference, but why do you recommend an alloy frame?

    Anybody have any recommendations on how to learn to use a sextant? I learn well from books if there are any that stand out.
    I tried several times to learn from books, and only succeeded with the text they use at Mystic Seaport: Practical Celestial Navigation, by Susan P. Howell. I think it's quite good --but given how many books are out there, and that I tried several without success, it's pretty much certain that one approach doesn't work for everyone.

    Mine was similar to a Tamiyah. I preferred it over more expensive instruments. Plath were a little heavy, and of course the plastic...Davis are too light, and difficult to hold steady. Best get one with a monocular rather than a simple lens. The monocular gathers light more efficiently and is easier in twilight. Also the slightly stronger magnification is better for putting the ' lim' on the horizon...sun and moon...
    I've heard about Tamaya; they seem to have a good reputation. All the ones on eBay seem to be in India (via the ship-breakers?), and I'm reluctant to buy from sellers there just because they're so distant there's no recourse if anything goes amiss. I've never held a Plath, but would be interested to, hearing this assessment. Yes, the Davis is much too light and jumps all over the place. That was my impression of the monocular type; good to have it corroborated.

    As for repairs, you have a few choices, but sextant and magnetic compass repair guys are getting rather hard to find these days.
    Try Bill Haimes, at Island Marine Instruments, Seattle. http://www.islandmarineinst.com/ Really good guy, and if he doesn't do the repairs, he'll know who does.

    My dad always preferred the Bendex Bubble Sextant.
    I thought bubble sextants were for aircraft navigation? Interesting. I'll have a look.

    Thank you all for the information. This all gives me a starting place for my pipe dreaming. Right now I actually have three sextants on my shelf: the plastic Davis, which is functional but not ideal; a plastic Ebbco (price 15p!), given to me by a friend who had inherited it from his father, and which I might consider a liferaft sextant; and a stunning 1902 Sewill, with all the bells and whistles of the time, that belonged to the father of my honorary grandmothers (the women who taught me to sail when I was 5) and that I daren't take to sea.

    Alex

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    Default Re: Sextants

    Quote Originally Posted by Pitsligo View Post
    Cool. I've got a search running now, just to see what turns up.



    Seeing "Zeiss" makes me cringe at what one must cost today, but I'll have a look around.



    I've heard good things about the full windth mirrors, but never played with one. Not questioning your preference, but why do you recommend an alloy frame?



    I tried several times to learn from books, and only succeeded with the text they use at Mystic Seaport: Practical Celestial Navigation, by Susan P. Howell. I think it's quite good --but given how many books are out there, and that I tried several without success, it's pretty much certain that one approach doesn't work for everyone.



    I've heard about Tamaya; they seem to have a good reputation. All the ones on eBay seem to be in India (via the ship-breakers?), and I'm reluctant to buy from sellers there just because they're so distant there's no recourse if anything goes amiss. I've never held a Plath, but would be interested to, hearing this assessment. Yes, the Davis is much too light and jumps all over the place. That was my impression of the monocular type; good to have it corroborated.



    Try Bill Haimes, at Island Marine Instruments, Seattle. http://www.islandmarineinst.com/ Really good guy, and if he doesn't do the repairs, he'll know who does.



    I thought bubble sextants were for aircraft navigation? Interesting. I'll have a look.

    Thank you all for the information. This all gives me a starting place for my pipe dreaming. Right now I actually have three sextants on my shelf: the plastic Davis, which is functional but not ideal; a plastic Ebbco (price 15p!), given to me by a friend who had inherited it from his father, and which I might consider a liferaft sextant; and a stunning 1902 Sewill, with all the bells and whistles of the time, that belonged to the father of my honorary grandmothers (the women who taught me to sail when I was 5) and that I daren't take to sea.

    Alex
    Mixter's Primer of Navigation includes chapters on using the bubble sextant and theAir Almanac Tables. Aircraft navigation requires efficiency and speed, and the tables are designed to make solving the problem easier.

    There is also Self Contained Celestial Navigation With H. O. 208 by John S. Letcher. It is designed for the small-craft mariner, and includes chapters on nautical and aircraft sextants, and has the tables at the back of the book.

    Celestial Navigation for Yachtsmen by Mary Blewitt, has been praised as a good place to start.

    Good luck, and Have Fun!
    Last edited by sharpiefan; 09-07-2017 at 01:50 PM.

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    Default Re: Sextants

    I have a Tamaya Jupiter. Haven't used it in anger in thirty years, but it was a fine tool when I did. I remember taking a noon fix off Venezuela once, marking it on the chart, and saying, "Hmm. There should be a buoy right -- there! And there it was.

    Best,
    Chris
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    Default Re: Sextants

    "All the ones on eBay seem to be in India (via the ship-breakers?), and I'm reluctant to buy from sellers there just because they're so distant there's no recourse if anything goes amiss."

    You betcha!

    Navigators generally take their sextants with them. Sextants are a personal bit of gear. I've seen a few USN sextants supposedly came out of the "mothball fleets," but the Indian sextants I've seen on fleaBay are almost all simply brass decorator pieces. They may look cool on your bookshelf, but they aren't navigational instruments. If the sextant is brass and not 150 or 200 years old, it's almost certainly a decorator reproduction. Tons of that stuff was (and still) is made in India for the export market.

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    Default Re: Sextants

    ...the Indian sextants I've seen on fleaBay are almost all simply brass decorator pieces.
    There are certainly a lot of those! However, if you search for <Tamaya sextant>, you'll see a lot of genuine Tamayas coming out of India. Or maybe they're counterfeit Tamayas, but they at least aren't the nauti-tchotchki. Some even have the 7x35 monocular.

    Navigators generally take their sextants with them. Sextants are a personal bit of gear.
    That has always been my understanding. Sextant, chronometer, and log are the Holy Trinity of the offshore navigator; onshore, it's the leadline, binoculars, and stopwatch. Of course the compass stays with the ship, and reigns above all...

    Alex

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    Default Re: Sextants

    Don't go with a bubble sextant. They are for aircraft and not suitable for a boat. The bubble is affected by acceleration. On a plane, acceleration is pretty constant and can be compensated for while it's difficult to know your height above sea level. On a bouncing boat deck, acceleration is all over the place and your height above sea level is easier to judge.

    I have been very happy with every Tamaya that I've ever used. I just didn't like the feel of the one Weems & Plath that I crossed the Atlantic with. YMMV.

    I learned with Dutton's and Bowditch. You won't get a simple step by step from either, but you will learn celestial navigation.

    Davis makes work forms for sight reduction. If you have a basic understanding of the process, the Davis form is close to step by step. You can practice taking sights while standing on a beach that has a clear horizon beneath the sun. On a calm clear day you can use a swimming pool or a still lake as an artificial horizon.

    You should be comfortable shooting the sun before you attempt a star sight. You have a limited time to find and shoot the star(s) you need while you still have a clear horizon. You'll need to learn how to use a star finder to find the azimuth, and pre-calculate the approximate altitude of your star(s) so you can point yourself to find it through the sextant's scope before it's visible to the naked eye.
    Last edited by SchoonerRat; 09-07-2017 at 06:58 PM.
    Schooner captains love to get blown offshore!

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    Default Re: Sextants

    [QUOTE=SchoonerRat;5338736]Don't go with a bubble sextant. They are for aircraft and not suitable for a boat. The bubble is affected by acceleration. On a plane, acceleration is pretty constant and can be compensated for while it's difficult to know your height above sea level. On a bouncing boat deck, acceleration is all over the place and your height above sea level is easier to judge.

    Dad always removed the bubble and striped some of the parts to get to a basic machine, very accurate and easy to read. Don't need the bubble if you're using the horizon. Works quite well.

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    Default Re: Sextants

    [QUOTE=J.Madison;5337393]Anybody have any recommendations on how to learn to use a sextant? I learn well from books if there are any that stand out.

    "Celestial Navigation for Yachtsmen" by Mary Blewitt is probably the most popular book for this over here. A slim and simple book. Dont know if its still in print but there must be lots of copies around.Its available on Amazon.

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    Default Re: Sextants

    For learning I went to a night school I wrote a thread about it].The book I used was for the course: Ocean Yacht Navigator, by Wilkes. It's British but the only difference is in the Almanac numbers. I liked the book, others swear by Mary Blewitt's book.

    I ran a poll on a FB site for former Yacht Professionals.A surprising number dead reckoned and used RDF offshore (there used to be a v powerful AM station on Montseratt, which made finding Antigua easy). If I remember about 15% did that, about half the remainder just did noon sights, and the rest did proper sights, but some of them used a dedicated calculator.
    Last edited by Hwyl; 09-09-2017 at 05:49 PM.

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    Default Re: Sextants

    My son is a professional and to my slight surprise the book he was given at college was the Admiralty Manual of Navigation, Volume Two.

    I took a look and it really is a masterpiece. I'd now recommend it over any of the yacht books.
    IMAGINES VEL NON FUERINT

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    Default Re: Sextants

    Aircraft sight reduction tables are the preferred system for small boat navigation. Unless you're doing your sights from a large stable platform, like a destroyer, the extra accuracy of the marine tables will be useless to you. If you don't want to go completely old school, you can use a navigation computer to do your reductions. On my last major delivery, I had a programmable HP calculator that I programmed with the sight reduction calculations. There was no need for an assumed position, most of the possibility of human error was removed from the process, and an accurate azimuth and altitude is quickly produced and easily plotted on a chart. But have your tables handy and know how to use them. Complete reliance on any electronic black box is asking for trouble.
    Schooner captains love to get blown offshore!

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    Default Re: Sextants

    Complete reliance on any electronic black box is asking for trouble.
    Amen!

    Dad always removed the bubble and striped some of the parts to get to a basic machine, very accurate and easy to read. Don't need the bubble if you're using the horizon. Works quite well.
    There's currently a Plath sextant on fleabay with a bubble attachment I find interesting (I have no connection to the seller, etc.): http://www.ebay.com/itm/Vintage-Germ...n/382217788689

    Seller is in Estonia. It isn't the right sextant for me, but it's an interesting idea.

    On the same note, my honorary grandmother's father wired a simple spirit level capsule to his Sewill sextant that's now on my shelf. I can't imagine it was hugely accurate, but it's an interesting modification. I suspect it was for when he was ashore, practicing.

    Aircraft sight reduction tables are the preferred system for small boat navigation.
    I've heard that from other people, too. I've used H.O. 229 in the past, and I've got a partial set of H.O. 214 I haven't yet used (grabbed it at a flea market because I had heard it's an excellent system), but I've also heard H.O. 249, for air navigation, can be easier to use.

    Has anyone played with Lunar Distance? I just finished re-reading Slocum and love it that his "chronometer" was a tin clock, and that the minute hand eventually fell off. He was, by all accounts, an extremely skilled navigator.

    Alex

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    Default Re: Sextants

    Forget lunar distances.

    There is a reason why, for two hundred years, shipowners, a class of men not known for their enthusiasm for spending money, fitted their ships with expensive chronometers. Lunar distances are almost impossible from a ship, and much harder from a small boat.

    I have a very nice C. Plath (which is not the same thing as a Cassens and Plath - also nice but different, and with no parts in common!) with a marine, not an air, artificial horizon attachment, but it's heavy and the mirrors are small and from a yacht you do better with full width mirrors and an alloy frame.
    IMAGINES VEL NON FUERINT

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    Default Re: Sextants

    When I was a kid learning in the back yard I needed an artificial horizon. Dad showed me how to put a large frying pan on a fence post of suitable height, carefully fill till the meniscus was over the rim, and sight on that as my horizon. Handy for practice inland.

    Dad had taught me to shoot with both eyes open, one sighting and the other in soft focus taking in the whole field. Similarly he'd taught me how to draw from a microscope with one eye on the ocular and the other on the paper. So it was natural to be shooting stars with a wide view. Even so, I at first kept losing a star as I brought it down. Dad pointed out that the angle was the same from star to horizon as horizon to star and the horizon's a bit big to lose. So I learned to crank the horizon up to the star, finding the star in general with my left eye before getting it into the right eye's view through that silly little telescope.

    I learned on a Davis lifeboat model, about $15 then, from the Air Almanac and never when actually at sea bothered with more than one minute accuracy anyway so that was just fine.

    It's actually fun to have the stars as friends, at least if you keep up. I am afraid my knowledge of the stars right now is at about the same level as my once fluent Latin and German. It's embarrassing.

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    Default Re: Sextants

    Well, sorry I went to the trouble to pull out all my celestial materials... Ciao.
    Last edited by Ed Harrow; 09-09-2017 at 07:46 PM.
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    Default Re: Sextants

    Noodling about on the internet, I found this .pdf for sight reduction forms, for HO 229: https://my.vanderbilt.edu/astronav/f...ction-Form.pdf I'm a tightwad, so being able to print my own, rather than order them from Davis, has a great deal of appeal.

    There is a reason why, for two hundred years, shipowners, a class of men not known for their enthusiasm for spending money, fitted their ships with expensive chronometers. Lunar distances are almost impossible from a ship, and much harder from a small boat.
    I didn't say I was going to rely on them, or even try it myself, I just wondered if anyone here had played with them. Since Slocum relied on them aboard Spray, it's clearly possible to work lunar distances on a small boat, perhaps even practical after enough experience (which he had a lot of), but it isn't as if *I'm* ever going to have the combination of knowledge and practice that would lead me to leave my chronometer ashore. It's a bit of a tangent from my OP, but since this is a multi-thread already, with J.Madison's query about tutorial, I thought I'd see what those who have done lunar distances have to say about it.

    I have a very nice C. Plath (which is not the same thing as a Cassens and Plath...
    That's good information. I'm not sure I had ever known they were two different animals. Thank you.

    Dad had taught me to shoot with both eyes open, one sighting and the other in soft focus taking in the whole field. Similarly he'd taught me how to draw from a microscope with one eye on the ocular and the other on the paper.
    Gotta say, I like the sounds of your dad.

    Alex

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    Default Re: Sextants

    Show me someone who says he has navigated using lunar distances and I will show you either an astronomer or a liar.

    Lunar distance tables were dropped from the Nautical Almanac in 1906.
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    Default Re: Sextants

    Show me someone who says he has navigated using lunar distances and I will show you either an astronomer or a liar.
    Today? Of course. In 1893, at the end of a long career in deepwater sail? Different situation.

    And I will reiterate: I was wondering if anyone here had played with them. Experimented, tried their hand, gotten frustrated, won a moment of triumph, sweated out the math in the backyard with an artificial horizon, etc. If no one has, that's fine and perfectly understandable. If someone has, I was hoping they might post something on what it's like. Difficult, I expect, but beyond that? It'd be an interesting post.

    But, like you, I seriously doubt anyone other than an astronomer or a complete celestial nav geek has relied on them exclusively in the last century. And in the last 25 years, since GPS became reliable, I would bet the vast majority of offshore navigators haven't even done much even by way of noon sights. This entire thread is predicated on what is arguably an anachronism. A very practical one, but an anachronism just the same. Who knows how anachronistically inclined some of the WBF members might be?

    Alex

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    Default Re: Sextants

    I took one of Mystic Seaport navigation classes taught by Frank Reed that taught lunars. Fascinating history and actually fun to shoot. Frank has a great calculator on his reed navigation.com site to solve the sights. It's pleasant practice to shoot lunar-planet distances or lunar-star distances at night in the backyard, use Frank's calculator, and see how accurate you can get.

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    Default Re: Sextants

    I took one of Mystic Seaport navigation classes taught by Frank Reed that taught lunars.
    Very cool! How difficult is it? Something you'd consider doing at sea? I'll check out that calculator --thanks for the tip.

    While I was working at Mystic Seaport I took a similar course, taught by Don Treworgy, but Don didn't teach lunars.

    Alex

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    Default Re: Sextants

    Taking the distance isn't hard, just very demanding on accuracy....calculating the solution reminds me of why i use an accountant to prepare my taxes. It's possible I might get the correct answer. Frank used Bligh's log entries to explain the process and then had us replicate a lunar from a worksheet he found on the Charles Morgan from a voyage in the late 1800's. When we students solved a series of tedious calculations to obtain a logarithm that matched an entry on that old scrap sheet that frank had put up on the overhead projector it was that 'moment of triumph' you referenced in your post. What I found to be fun was It allows practice in the evening when the kids are to bed and I dont need to fuss with generating a horizon.

    As to real world navigating with lunars it isnt remotely appealing to me. it would require a sizeable vessel to have sufficient stability at sea to be consistently accurate and plenty of free time. A chronometer (or two) are readily available now, aren't as fragile, time checks via radio is easy and the lunar after all is only supposed to be used as a monthly check to correct the clocks.

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    Default Re: Sextants

    By the way, I just remembered that a sextant can also be used for coastal navigation. Turning it on its side, you can get the angle between two landmarks. Determining the angles between any three or more identifiable landmarks allows you to plot a position.

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    Default Re: Sextants

    Quote Originally Posted by Andrew Craig-Bennett View Post
    Show me someone who says he has navigated using lunar distances and I will show you either an astronomer or a liar.

    Lunar distance tables were dropped from the Nautical Almanac in 1906.
    I used a lunar twice. For fun really, but it was a complicated and long calculation. Having done it I have no desire to repeat. Actually I doubt if I could without a serious brush-up.

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