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Old 10-29-2018, 10:35 AM   #1
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Sextants in general

Anyone use a sextant as an aid for navigation?
If so, the make and model sextant do you use and what books do you recommend to learn how to use a sextant.
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Old 10-29-2018, 10:42 AM   #2
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Years ago I was introduced to a sextant and its uses. I was impressed favorably.
Today, I own an Astra IIIB sextant and realize my "introduction" was too many years ago so I am basically starting from 0 (zero).
I have not found a book titled "Sextants for Dummies". I am seeking a list of recommended books etc so again, I can learn the magic of the sextant.
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Old 10-29-2018, 12:58 PM   #3
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Besides shooting stars, planets, moon and the sun, a sextant turned sideways to measure angles between objects giving an extremely accurate position. Using a 3 arm protractor and 2 angles, plotted on a chart gives a position probably within inches. In tight places, I think the fix is better than GPS. In the USN, I navigated thru a minefield in a known channel using this method.

I like to anchor in remote, quiet places. Most not used by other boats. Using this method I scout a cove and if necessary plot individual rocks with my small boat so I can bring in the big boat safely where others fear to go. And it's quiet!
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Old 10-29-2018, 01:07 PM   #4
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Anyone use a sextant as an aid for navigation?
If so, the make and model sextant do you use and what books do you recommend to learn how to use a sextant.
I have taken the US Power Squadron navigation courses, JN (Junior Navigation using sun and moon) and N(avigation) using stars and planets. I could not have learned from a book (at least not easily). The instructors went with us when we shot our sights which helped immensely. The courses are not easy...my Navigation take-home exam took me 40 hours to complete!

I would check with your local Squadron to see if they offer either JN or N in your area.
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Old 10-29-2018, 01:12 PM   #5
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GPS is so accurate, some charts are useless in close quarters.....but most if the time it will put you within a meter or two.

Doubt many could do that with a sextant and triangulation...close but only close.

However that could be a good thing on some charts depending on what method of positioning was used for the chart soundings.
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Old 10-29-2018, 01:56 PM   #6
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Realistically, a sextant is just a toy now. I understand that the naval academy doesn't require celestial navigation any more.

Many years ago, before I owned a cruising boat and before GPS's became available to mariners I bought a medium quality Davis sextant and played with it on my parents front porch which had a wide view of the Gulf of Mexico.

At first I was off dozens, sometimes hundreds of miles. Later I narrowed that down to 5 miles or so which I figured would let me find an inlet if I were coming in from offshore. But that accuracy was obtained with a solid perch on a house deck. Who knows what kind of accuracy you would get with a boat pitching and rolling, certainly no better than 10 miles.

I first used the basic government tables- it took two different sets of tables used together with logarithm tables to do the math. It was easy to make a mistake. Then I got a proprietary set of tables that combined everything in one book. It was easier and required less math. I think it was George Bennett's The Complete On-Board Celestial Navigator. That was somewhat easier and less prone to math mistakes.

Then there are the apps that run on Androids and Apples that do the sight reduction by plugging in time and declinations. But why would you want to depend on a device that will get you within a few feet if it is working. Well, why would you want to depend on some out of date tables either.

So, buy a sextant to play with and enjoy the idea of doing something that only ship's captains of yore could do. But forget about real world navigation with a sextant.

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Old 10-29-2018, 02:44 PM   #7
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Realistically, a sextant is just a toy now. I understand that the naval academy doesn't require celestial navigation any more.

Many years ago, before I owned a cruising boat and before GPS's became available to mariners I bought a medium quality Davis sextant and played with it on my parents front porch which had a wide view of the Gulf of Mexico.

At first I was off dozens, sometimes hundreds of miles. Later I narrowed that down to 5 miles or so which I figured would let me find an inlet if I were coming in from offshore. But that accuracy was obtained with a solid perch on a house deck. Who knows what kind of accuracy you would get with a boat pitching and rolling, certainly no better than 10 miles.

I first used the basic government tables- it took two different sets of tables used together with logarithm tables to do the math. It was easy to make a mistake. Then I got a proprietary set of tables that combined everything in one book. It was easier and required less math. I think it was George Bennett's The Complete On-Board Celestial Navigator. That was somewhat easier and less prone to math mistakes.

Then there are the apps that run on Androids and Apples that do the sight reduction by plugging in time and declinations. But why would you want to depend on a device that will get you within a few feet if it is working. Well, why would you want to depend on some out of date tables either.

So, buy a sextant to play with and enjoy the idea of doing something that only ship's captains of yore could do. But forget about real world navigation with a sextant.

David
David, I took a 14 day repositioning cruise on an ocean liner.
They had on board tours available, for a price. Part of the tour was on the bridge. There sitting on a table behind the steering position was a wooden box..... I laughed and said, I recognize that..... houses the sextant.

I read recently, the Naval Academy is again teaching celestial navigation.

The sub I was on, had 3 SINS units..... When along side the tender, they would calibrate the SINS ..... which resulted in many long hours for the nav people. Then knew we were close when they got within the length of the beam of the tender. LOL
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Old 10-29-2018, 02:54 PM   #8
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I learned from my dad using a plastic Davis sextant. My sailboat had a Racal "Transit" satnav system, so fixes were hours apart and not always reliable. The little cocked hat on the chart was much more confidence-inspiring with celestial correlation in agreement with that old British mystery box.

I've toyed with the idea of getting another one, and agree entirely with the utility of plotting horizontal angles, though a pelorus or hand bearing compass does the same job for much less money.

Oh, BTW...the two books on my shelf that I found useful are the classic "Celestial Navigation for Yachtsmen" by Mary Blewitt and "Self-Taught Navigation: Ten Easy Steps to Master Celestial Navigation" by Robert Kittredge.
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Old 10-29-2018, 03:50 PM   #9
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Years ago I was introduced to a sextant and its uses. I was impressed favorably.
Today, I own an Astra IIIB sextant and realize my "introduction" was too many years ago so I am basically starting from 0 (zero).
I have not found a book titled "Sextants for Dummies". I am seeking a list of recommended books etc so again, I can learn the magic of the sextant.
Why bother, but if you do want to bother,George Buehler (diesel Duck designer) had a simple book on how to.
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Old 10-29-2018, 04:13 PM   #10
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Back in our days sailing I used the Davis 25 I believe it was called way before GPS was available. Like David my first sights had me 50 +- but with more practise got it down to 5-10 miles. I also used a Zenith Transoceanic radio direction finder on the way to Bimini to backup dead reckoning and sailed the radio signal right on course to Bimini. That radio direction finder was great keeping you on course thru the gulf stream.
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Old 10-29-2018, 05:14 PM   #11
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When I was a Snipe in the early 80s I always enjoyed watching the Deckies using their Sextants and would try it periodically. Fun stuff. As others have noted for us rec boaters there are modern, cheap GPS units available that are much more accurate than anything, including dead reckoning. If the satellites go down, then we all have much bigger problems to worry about than our position.
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Old 10-29-2018, 06:03 PM   #12
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I have taken the US Power Squadron navigation courses, JN (Junior Navigation using sun and moon) and N(avigation) using stars and planets. I could not have learned from a book (at least not easily). The instructors went with us when we shot our sights which helped immensely. The courses are not easy...my Navigation take-home exam took me 40 hours to complete!

I would check with your local Squadron to see if they offer either JN or N in your area.
Same here. I always checked my sights with a GPS and decided a few years later to sell the sextant and have a spare GPS in a Faraday Cage. Took three years to pass the two Squadron course. Learned a lot other than how to use the sextant. Best thing to come out of it is that I still see a couple of my classmates every week.
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Old 10-29-2018, 06:15 PM   #13
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Being the closet Luddite that I am, I have often thought it would be a good mental exercise to learn to use a sextant. However, I always boat in sight of land. This means that it is only very rarely that I see a horizon over the water. Too many hills and mountains. So, I've never bothered. I have and do use a handheld sighting compass for taking bearings to find or check my position. It isn't as accurate as a sextant, but then I am usually under way at the time and so my bearings aren't all that accurate so the increased precision of a sextant wouldn't make much difference.
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Old 10-29-2018, 10:25 PM   #14
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Many (many!) years ago I was a quartermaster in the Navy, serving in a destroyer after boot camp and basic QM fleet school. They didn't teach celestial at the school, just basic nav principles, chart reading, etc. Later aboard ship, assisting the navigator with noon and evening sights, I became interested enough to teach myself by reading our chartroom copy of Bowditch's American Practical Navigator. Not the best way - as mentioned earlier, even with a formal course it can be tough going.


I occasionally think it might be fun to refresh myself on it just as some archaic, esoteric skill but, as also mentioned earlier, it's of no practical use for coastwise navigation; maybe if you're going way offshore as an extremis backup to GPS. I think the best fix I ever got was still only within a three mile accuracy (checked against a LORAN fix).
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Old 10-30-2018, 12:16 AM   #15
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Years ago I was introduced to a sextant and its uses. I was impressed favorably.
Today, I own an Astra IIIB sextant and realize my "introduction" was too many years ago so I am basically starting from 0 (zero).
I have not found a book titled "Sextants for Dummies". I am seeking a list of recommended books etc so again, I can learn the magic of the sextant.
Dan, this is quite good:. https://www.amazon.com/Miranav-workb...D-L&ref=plSrch

I also have the same Astra and know how to use it. We're all one lightning strike away from needing it when off shore.
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Old 10-30-2018, 09:22 AM   #16
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also have the same Astra and know how to use it. We're all one lightning strike away from needing it when off shore.
I am all in for learning new skills, and think anyone who can use a
Sextant is the type of mariner I respect. However, how is a lightening strike going to knock out all of our GPS? I have two Furono MDF’s as primary, and 3 iPads and a phone that all contain a GPS device and run Navionics and one other program to determine my position as back ups. Could a lightening strike take them all down? Do you have a source or article to reference where this has occurred? If a real threat, I would think there are multiple instances of occurrence that can be referenced.
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Old 10-30-2018, 11:30 AM   #17
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Reliance on GPS chart plotters today triggered a related debate on this forum a few years ago about ditching paper charts and totally relying on electronics. The issue of lightning strikes was vigorously debated.


Jeff Siegel, the originator of Active Captain argued that with several redundant devices on board, the chances of all of them being put out of commission due to lightning was nil. He also noted that you can keep one of your devices in the microwave which acts like a Faraday cage and shields anything inside from the effects of lightning.


I finally agreed with Jeff and stopped using paper charts.


I doubt if you will find a case of lightning destroying 3 or 4 gps devices at once and certainly none where a device in the microwave was destroyed.



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Old 10-30-2018, 01:03 PM   #18
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I am all in for learning new skills, and think anyone who can use a
Sextant is the type of mariner I respect. However, how is a lightening strike going to knock out all of our GPS?
Yes, lightning can take out your devices with a direct power hit or via EMP.

The question is what are the odds? I believe it was BoatUS that has numbers showing that multihulls are about twice as likely to get hit by lightning that mono hulls. They list the odds on a variety of boats types.

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I have two Furono MDF’s as primary, and 3 iPads and a phone that all contain a GPS device and run Navionics and one other program to determine my position as back ups. Could a lightening strike take them all down? Do you have a source or article to reference where this has occurred? If a real threat, I would think there are multiple instances of occurrence that can be referenced.

The EMP from lightning is quite powerful. Devices do not have to be connected to power sources to get taken out. If you search the web I am sure you can find plenty of references of boats and houses being hit and loosing some or all of their devices. I think one of the Nordhavn 63's was hit around VA and it took out all of their devices and I remember a large sailboat in the Baltic that got hit with the same results. Back in the day, my dads boat was hit and lost all power equipment which was not much, the depth sounder, VHF radio and lights, but it was all toast.

A microwave can help protect devices but it is better to put the devices in a sealed metal container with NO gaps. According to a book on EMP I read, wrapping in multiple layers of aluminum foil works well.

There is a similar discussion on Cruisers Forum that was active this week on this subject. I believe lightning was being discussed in conversation about the need for paper charts.

Later,
Dan
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Old 10-30-2018, 01:05 PM   #19
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I am all in for learning new skills, and think anyone who can use a
Sextant is the type of mariner I respect. However, how is a lightening strike going to knock out all of our GPS? I have two Furono MDF’s as primary, and 3 iPads and a phone that all contain a GPS device and run Navionics and one other program to determine my position as back ups. Could a lightening strike take them all down? Do you have a source or article to reference where this has occurred? If a real threat, I would think there are multiple instances of occurrence that can be referenced.
Anything wired to ship systems can be fried in a lightning strike, but you are quite right that handheld, battery powered devices may survive. As long as the satellites are online. I guess the point is that I don't expect to be holed, but have water tight bulkheads/doors, nor sink but have an ACR. Having a sextant on board, with a Starpilot calculator to reduce star sights that will get you within a couple of miles of your position, (and God forbid the paper tables for noon sights) gives you something enjoyable to do at dusk/dawn. Self sufficiency has long been considered a virtue for the blue water sailor. Not sure why that should necessarily end at GPS's door.
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Old 10-30-2018, 01:15 PM   #20
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Instead of being worried about a lightning hit, I'd be more worried about a solar flare interfering with the GPS signals from the satellites or even taking out the electronics in one of those satellites. It is always good to have more then one form of technology on board for safety issues. One of the reasons I keep paper charts.
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