Lost tech of Ancients

Discussion in 'OnBoard Electronics & Controls' started by Yobarnacle, Dec 10, 2011.

  1. Yobarnacle
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    Yobarnacle Senior Member

    The most important navigation instrument on the bridge is the EYES of the navgator.
    And the most important computer on board is between his ears.

    No electronic or mechanical device can out perform or replace the watch officer.
    All these wonderfull devices we love are "Aids to Navigation Instruments". Without a knowlegeable

    operator, they are just expensive wheelhouse jewelry.

    There is a book industry, sucessfull authors who write about mysteries and possible lost technologies of

    ancient egyptians, or mayans, or atlanteans.

    Will future authors write about our lost technologies?
    The sextant is another high tech jewel, usefull only as decor unless you can use it.

    Many folks today are victims of an ancient hoax. The "Myth" that navigation is hard. It's nearly black magic!

    Requiring dangerous studies of the arcane, BEWARE! Stirring and mixing mystical, uncomprehendable,

    mathematical formulae in the caldron of your skull will drive you mad!
    Sorcerors have stars on their pointy hats, right?

    Truth? Navigation was an early industrial secret. Deliberately shrouded in mystery and initiation restricted

    to the upper class.

    Life was rough for common seamen in the days of sail. Officers frequently abusive. The only thing kept the

    men from chucking officers over the side, was "Who would navigate?" Never was a mutiny unless an officer

    mutinied with the crew; ie Christian on the Bounty.

    Lesson #1 Finding latitude from Polaris, the north star.
    The altitude of polaris is equal to your latitude.
    Difficult, huh?
    If polaris is 34 degrees above the horizon, your latitude is 34 degrees north.
    Polaris isn't precisely over the north pole, but wobbles a bit. The difference is always less than a degree

    and the almanac has 3 small tables of corrections, together on one page, to refine that less than degree

    error. The greatest error you'll probably encounter is your balance on a small boat underway.

    Lesson #2 Finding latitude from the sun.
    Zenith distance of the sun when due south is equal to your latitude.
    Difficult, huh?
    Zenith is directly overhead. Because we observe the sun south of us, the altitude of the sun would tell us

    how far south we are. We measure latitude in how far north we are (in northern hemishere).
    So. We subtract the suns altitude from 90 degrees and get Z or latitude north.
    We do need to correct for the season, since the earth wobbles. During summer between march 21 and

    september 21, we need to add the declination of the sun to Z to get our latitude. In winter half between same

    2 dates, we subtract.
    Declination is the latitude of the sun. It's listed each day in almanac. Instead of having to keep track of 2

    latitudes, for the sun and yourself, they named the suns latitude "declination". Latitude is yours, declination

    the suns.
    Mechanics of shooting noon sun is to start measuring before and continue measurements untill sun stops

    rising. When starts descending, your highest recorded altitude and time is LAN. Local apparent noon. Also

    called meridian transit, when the sun was due south of you.
    Learning the terms and language of navigation is the hardest part. As you see, the math isn't hard at all.

    If there is interest, I'll post final 8 lessons in celestial navigation.
     
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  2. hoytedow
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    hoytedow Wood Butcher

  3. hoytedow
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    hoytedow Wood Butcher

  4. Yobarnacle
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    Yobarnacle Senior Member

    Thanks Hoyt. I'll continue then.
    As Hoyt points out early navigators didn't use sextants. Nor did they have chronometers. Untill you could know accurate time at sea, figuring longitude was impossible. Our forbears relied on parallel sailing.
    Captains originally weren't seamen. If doctors are specialized today, they adopted the concept from old ships. The captain was a military man expert in battle tactics. Serving him was a sailing master expert in ship handling, and a pilot expert who navigated. Pilots had rutgers. A secret journal they maintained with the recorded latitudes of various ports, points, headlands, and islands. The course was north, or south, untill you "fetched" the correct latitude, then east or west "hauling" along the parallel untill arrival your destination.

    Lesson #3 The noon position. More than the latitude can be learned from LAN, if you have an accurate clock. Cheap radio corrected Atomic clocks are available. Also cell phones and computers auto update time.
    The world is 360 degrees around and revolves once in 24 hours. Obviously each time zone is 15 degrees wide.
    It starts in Greenwich, England. Greenwich time zone extends from 007 degrees 30 minutes west longitude to 007*30' E longitude. It changes every 15 degrees there after.
    Longitude is marked with greek letter lamhda, like upside down y and latitude with capital L. I don't have lamdha on my keyboard.
    The almanac lists information based on Greenwich time. To make navigation easier than going east and west of greenwich as longitude does, they show greenwich hour angle, GHA. Its degrees from Greenwich measured west 360 degrees circling globe in one direction.
    If you accurately know Greenwich time of your LAN, converting hours and minutes of time into degrees and minutes of GHA gives you your distance from Greenwich. If your GHA is less than 180, its the same as W longitude. If youre in the Pacific ocean, GHA greater than 180, then subtract GHA fro 360 and you have E longitude.
    Now you see why LAN is so important. You learn both your latitude and longitude from observing a single celestial body, the sun. Which is almost always visible in daylight hours. :)
     
  5. gonzo
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    gonzo Senior Member

    I've gone for up to nine days without a sun sight in the tropics. The noon position is good for latitude and gives a rough longitude. However, it takes a lot of time and is very dependent on a good sight at noon. The noon average is more reliable. You take a series of sights in the morning, then set the sextant for the same altitude in the afternoon. Noon is the time in between the sights at the same elevation, corrected for distance traveled.
     
  6. Petros
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    Petros Senior Member

    Up here in the Pacific Northwest we can go many days of overcast, similar in other far north and south locations. It could be a week or more before you get a chance to take a reading on either sun or stars. Modern electrictroic "assist" can still be very useful.

    But I agree, knowing how to locate yourself with simple knowlage and a few tools is what should come first if you expect to beable to navigate. I know after using my GPS on long road trips I do not always have a good feel for where I am as compared to using a map, espcially in a new city. IT is too easy to follow directions on a small screen rather than study a map and learn the layout of a new city.

    In Tim Severin's book about the Voyage of Sinbad (where he duplicated the 14,000 mile voyages of early Arab sea traders), he used a simple navigational tool, invented by Arab mathematicians, to find his location; A string with a wood or cardboard square on the end. one end of the string goes in the mouth, and than the square is held at arms length where the edge is lined up by eye with the horizon. Marks on the edge of the square would indicated degrees where the shadow of the string passed off the edge of the square. I do not recall the exact method used but he found it was accurate to within a degree, it was good enough to make land fall after crossing the Indian Ocean. With a simple device, and knowledge on how to use it, long crossings can be done safely.
     
  7. Yobarnacle
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    Yobarnacle Senior Member

    thanks Gonzo
    My intent is to "gently" introduce sextant navigation as a back up to failed electronics, dead batteries, turned off or corrupted data transmit from GPS satelites in national emergency.

    Lesson #4 Correcting sights.
    The above 3 lessons are simplified in that they are true with observed altitudes but neglected to explain how to acquire ho, the abbreviation for observed altitude.
    What you measure with your sextant is the sextant altitude. Sextants can have errors. Today with CNC you have a better chance of buying a perfect sextant than ages past. To determine if sextant has error, line up images in the sight, then check sextant reads 0. If not, sextant is usable but has an error. If error is on the arc you subtract the error from the sextant altitudes. Iff error is less than 0, off the arc, then add error to sights.
    Next, height of eye. Your height above sea level affects distance to visible horizon and your height above horizon in degrees. Inside the covers of almanac are tables to compesate for your height above sea level. again simple addition subtraction.
    The objects altitude above the horizon also affects the sight, because the more atmosphere between you and it, the more refraction. Just as a stick poked in the water appears bent. So, there is an altitude correction
    to be applied. Still sinple math.
    Eventually you will discover after much practice, your sights all seem to be a tad low, or a tad high. This is a personal error you can correct for. Everybody has one. May take years to derermine how much to correct for.
    anyway, applying these corrections to your hs gives you ho.
    anybody need clarification of recent posts?
     
  8. Yobarnacle
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    Yobarnacle Senior Member

    lesson #5 Obsolete technology.
    Besides a sextant, a plastic star finder 2102-D is a valuable asset. Eventually you'll become acquainted with the navigation stars, as they are the brightest in the heavens. Determining what star to look up in the almanac, requires 1st identifying the star. On a hazy evening or morning, if only a few stars visible, identification by eye is difficult. 2102-D is simple to use and comes with instructions in a pouch weighing less than a pound.
    I mentioned evening and morning. I saw a cartoon about an HR person interviewing a prospective employee. The applicant states he is interested in the navigators position, but doesn't work nights. Point of the toon was HR folk needed to know something about the position they wanted to fill. Stuck in my head, because I have long wondered if the cartoon artist was aware, no navigator works nights. Not only the stars but a clear horizon needs to be visible to shoot. Evening stars are shot during evening twilight, and the next sights are in morning twilight shortly before sunrise.

    Also very helpfull identifying stars is, Ho 249, Selected Stars for Air Navigation. One volumn with tear out daily pages. Open cover and theres todays stars and there data.

    Obsolete tech? I consider HO 229 obsolete. You need to learn how to use 229s to pass coast guard examinations, but they are cumbersome. It takes 6 volumns, each covering 15 degrees of latitude to cover globe. 229 is only tabulated for whole degrees of LHA and latitude and you have to interpolate in between and use assumed positions. Navigation isn't difficult if you eliminate 229s.
    Solution is a simple student calculator, light powered, with trig functions. About $15 at corner pharmacy.
    Intriging that you don't need to know trig to use it. For non-mathematicians, the definition of sin, cos, tan are buttons on your calculator. When you see the function in a formula, hit the named button.

    There are 5 more posts to wrap up sextant navigation. I'll stop here unless some one wants the rest of the explanation
     
  9. hoytedow
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    hoytedow Wood Butcher

    Don't stop. Do you have information on illuminated sextants with "artificial horizons"?

    Here is some reading material while we wait for another posting from OP.

    http://www.longcamp.com/horizon.html
     
  10. gonzo
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    gonzo Senior Member

    The 249 for air navigation is accurate enough to use in small boats. The 411 is a small book that also works fine.
     
  11. hoytedow
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    hoytedow Wood Butcher

  12. Leo Lazauskas
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    Leo Lazauskas Senior Member

    There are some fascinating theories, devices, techniques and strategies used by prehistoric navigators in a very recent book by my friend Charles Pearce.

    "Oceanic Migration: Paths, Sequence, Timing and Range of Prehistoric Migration in the Pacific and Indian Oceans", Pearce, Charles E.M., and Pearce, F.M.

    A synopsis can be found at:
    http://www.springer.com/social sciences/population studies/book/978-90-481-3825-8

    Quite a few pages can be read online for free from that url.
     
  13. Yobarnacle
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    Yobarnacle Senior Member

    Thanks Hoyt. There are all kinds of sextants available. Platic, aluminum, bronze, paper. Scoped and un-scoped.
    I learned on a cardboard Navy surplus training sextant when I was a teenage sea scout. Was very stiff waterproofed cardboard.
    Aircraft sextants have (or maybe had) bubble horizons built in because of their extreme (compared to sea level) altitudes. Never used one. In appearance resembled an old 8mm movie camera. I have no idea if any are still around other than in collections. WWII gear.
    I used to own an aluminum japanese made sextant, 2X scope, attached stop watch, in a teak case. I sold it, and for past 20 years demand office put a sextant on board. Flying to and fro around the world to rejoin vessel, or go home, you need to limit carry on luggage, cause only a durn fool would check a delicate optical instrument.
    Tradition style nauticle sextants are best. In use, you rock the sextant so the sun or star is arcing above horizon, just touching horizon at bottom og swing. Traditional sextants have best balance/feel for this. A 2X or 4X scope, and complete set of filters for looking at sun. A sturdy case is important, cause as I said it's a delicate instrument
     
  14. Yobarnacle
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    Yobarnacle Senior Member


  15. Yobarnacle
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    Yobarnacle Senior Member

    Lesson #6
    Ok scare time. I'll introduce you to a formula, one of 2 that I memorized a long time ago. These are shown at the bottom of every page of HO 229. With the caption, the above tables were calculated with the following formulas.
    You don't need to memorize them. Glue them on back side of the student calculator under some transparent tape.

    They are simple to memorize, tho. No more difficult than a phone number. If someone said, heres a phone number that will save your life, thered be a motive to remember it.
    Well, the formula has 3 sines and 3 cosines. Like this

    sin sin sin cos cos cos

    the 1st sin is the result so insert an equal. Also since the result is a sin, you need to convert it back to degrees. invert sin is written thus

    -1
    sin = sin sin cos cos cos

    Now I mentioned Latitude and declination. These go in the formula twice each. the last cos is LHA, local hour angle. Its the difference beteen your GHA and GHA of heavenly body. Thus
    -1
    sin = sinL sin dec + cosL cos dec cos LHA

    This formula gives you the hc. The computed altitude.
    You don't need interpolation or assumed positions like HO 229.
    Use your Dr position.
    Use the DMS buttom on calculator to convert degrees, minutes, seconds (DMS) to decimal degrees

    Reading the formula sounds like this. Computed altitude is Invert sin equals sin of latitude times sin of declination plus cosine of latitude times cosine of declination times cosine of local hour angle.
    A mouth full, huh? don't fret, just enter the numbers and hit the calculator buttons in order and it works.

    The same formula is used to calculate great circle distance. I'll explain in a later post
     
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