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Thread: Navigation

  1. #1
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    Default Navigation

    GPS... can find you within about 3' of your real location.

    Sextant... if you're good at taking sights (I'm not, yet) you can likely get within a few miles of your precise location.

    I've spent the last five years saving money, getting rid of crap at my house, now I'm rebuilding a basement (sigh) and I've spent time learning to sail, practicing, and understanding the physics of sailing.

    Somewhere in there I've picked up some diesel mechanics (not much yet, but simple trouble shooting), plumbing (enough to rebuild bathrooms!), knots, knot work, net making, knife making (trust me it has to do with sailing), "Rules of the Road", safety and many, many other skills associated with skippering a boat around a pond, lake or across an ocean.

    What I have NOT "grasped" yet is celestial navigation. Oh, I understand the basics. I can accurately determine my Latitude at night using the North Star (polaris) and I have the mechanics more or less firmly planted in my mind on calculating my longitude from time (Noon sun sight for instance) and doing most of the math.

    But, really, I have yet to take a sextant (I have two plastic sextants) and make a real sight and do the calculations.

    You need to have a horizon to see. I can see mountains to the south, west and north of me. Houses to the east. No horizon. So need to build an "artificial horizon" (pretty easy, water in a pie tin should do it, or cooking oil).

    I have bought somewhere around $200 worth of books, all taking a different direction on explaining celestial navigation.

    But in a nutshell (a small one) I learned the most important thing I've ever learned:

    Navy guys using the sextant on a ship and being competitive, practicing and trying to out-do one another RARELY got closer than 10 miles - which they considered "Good Enough". Occasionally someone could get within a mile (Fantastic).

    If I am crossing an ocean why do I need to be more accurate than 10 miles again? I don't!

    All I need to know is roughly where I am - as long as I'm not headed directly for a shoal water, reef, island chain I'll crash into.

    When you are close enough to hit an island or see reefs, you USE YOUR EYES!

    Seriously, I have spent all this time preparing for this and reading everything I can read, absorbing as much as I could and by normal, common sense, I already knew all this. I couldn't see a need to use a sextant in a lake. No need at all. I can use a compass to take bearings off objects on the shore and plot my location based on that on a map. No problem.

    What is it about using a sextant though that has bugged me so much the past couple of years?

    Easy. Math is not my BEST subject, I've always hated it to some degree and almost every, single text on the subject explains the details IN DEPTH of HOW celestial navigation works.

    Ok - to make you all get this like I finally did.... do you NEED to know how an internal combustion engine works to drive a car? Hell no.

    If you can get a simple step by step instruction on how to take the sight, correct for errors (Dip, Index, refraction, etc) then fill in a set of numbers from a book (or use a calculator that has the tables in it) and plug in numbers - then you can figure out where you are, within reason.

    Why bother with all of this?

    Simple.

    GPS units are electronic, as are computers, calculators, chart plotters, and numerous other electronic devices requiring batteries or electricity of some sort to work.

    If you take a lightning strike, the chances of your stuff working is pretty low after that. EMP will take even your hand held units off line.

    So.. knowing Celestial navigation using a sextant, watch and some tables is good to know.

    Even if it is "hard to do".
    Libertatem Prius!


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  2. #2
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    Default Re: Navigation

    Books I have, own, borrowed and have read:

    http://www.amazon.com/Celestial-Navi...2427370&sr=1-3

    http://www.amazon.com/Celestial-Navi...2427370&sr=1-4

    The second one, "For the Clueless" is a pretty good book. I have spoken too, and corresponded with the author. He is a very nice guy, and was extremely helpful with getting the forms up on a web site (I bought the digital version from Amazon, about 7 bucks)..... I HIGHLY recommend it, if you're interested in this subject.

    Book one above by Mary Blewit is a very narrowly focused text book (about 90 pages maybe) and it is pretty clear.

    But what I was missing and is filled by Jeremy Bernal's book is the "HOW TO" part.

    Knowing the basic theory of mechanics is great, but it doesn't help you drive the car, only fix it.

    Pretty good:
    http://www.amazon.com/Celestial-Navi...2427370&sr=1-6

    Have this in digital format (in a PDF file... I won't say from where):
    http://www.amazon.com/Celestial-Navi...2427370&sr=1-9

    http://www.amazon.com/Emergency-Navi...427370&sr=1-11

    This book you can get free (I'll give the link in a second):
    http://www.amazon.com/The-American-P...427671&sr=1-15

    Bowditch: The American Practical Navigator is a very OLD book, and was started by Nathaniel Bowditch in the late 1700s. It has been updated since then and is now taken care of by National Geospatial Intelligence Organization. The actual link to read the book online, or download either the entire manual or chapters is here: http://msi.nga.mil/NGAPortal/MSI.por...2&pubCode=0002

    Bowditch is a 35 Meg PDF. I have a hard copy, and several soft copies on various devices (both kindles, two computers, on a flash drive and at work).

    http://www.amazon.com/Celestial-Navi...427930&sr=1-32

    A required manual for Cel Nav.. need this to look up the positions of sun, stars, moon, planets, etc. This book is needed to produce some numbers for your calculations to determine your location.

    You will also need a sextant of course.

    I have read a lot more books on this subject, and many dozens of forums about Celestial Navigation. I will point out that everyone who sails from their arm chairs at home highly recommend a "metal sextant" and they want you to buy a REALLY expensive one.

    Don't do that.

    I bought two cheap plastic Davis models on eBay. From my reading I have found that you're not going to get closer than a mile or two no matter how accurate your equipment. Even several Navy guys I've spoken to and READ about say that "10 miles was close enough" on the ocean.

    So - why use this stuff when you have GPS? GPS can be shut down, altered to be inaccurate by the US Gov. It could go off line with EMP, solar storms. Lightning strikes can take it out. If you're at sea with little idea of where you are, celestial navigation can get you home or to a safe harbor.

    Lewis and Clarke used sextants to help them survey and travel, locate themselves across the country as well. Columbus used it to get to America, and back home again.

    So... my thinking is, like any survival skill, you learn a subject and know it well enough to use it when you need it - but you do not have to RELY on it. Like making a fire, finding water, hunting small animals and skinning, cleaning etc. You see, like anything else, this is a good skill to have and know - but like any OTHER skill you sometimes need tools to get you going.

    Hope this helps someone in the future!
    Libertatem Prius!


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  3. #3
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    Default Re: Navigation

    HAHAHAHAHAHAHAHAHAHAHAHAHAHA OMG SO EASY!!!!!!!!!!!!!!!

    What the HELL is wrong with him, you ask?

    Nothing.

    I just had a light come on.

    I've been 'struggling" with celestial navigation for months (well, two years). I have a plastic sextant and I just don't have enough time to sit and grasp all the math.

    But something happened. I was re-reading some stuff the other.

    In Celestial Navigation you use stars, the sun, planets and moon to ascertain your location.

    BASICALLY - you can (assuming you have the sun available in the day time) take what's called a "Noon Sight" and get both Lat and Longitude. Right?

    What if you drop your damned sextant over board, break it, or step on it?

    YOU DON'T NEED A SEXTANT as long as you have an accurate watch set to UTC/GMT/UT/Zulu time, and you know how "off" it is (Mine gains almost exactly 3 seconds a day), a horizon, and a star, or the sun!

    So... when the sun RISES in the morning, or SETS at night.... and you have an accurate watch, you mark the time the upper or lower limb JUST kisses the horizon!

    You just took a time, at the zero angle! You still have some math to do - but you don't have to recalculate the heights, angles and all the other crap. It's ZERO!

    LOL

    Wow.

    And yeah, that will work. And yes you can use a star. And yes you still have to have some other information from the almanac. But you can indeed plot a line of position!

    (Now, back to our regularly scheduled programming....)

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