Lost tech of Ancients

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

  1. Yobarnacle
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    Yobarnacle Senior Member holding steady course

    No Bowditch? Of course, it's "The American Practical Navigator", but practically everyone has permision to use it. :)
     
  2. michael pierzga
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    michael pierzga Senior Member

    The problem is that all those publications... HO 249, plotting sheets or whatever.... are ancient biblical scripts...you would probably have to voyage inland and purchase them at a museum shop. They just arent avaible in marine stores these days. Even paper charts are hard to find.

    I suppose you could download off the internet , print out, organize and save for a rainy day
     
  3. Yobarnacle
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    Yobarnacle Senior Member holding steady course

    OK, back to work
    Lesson #8
    Back in #6, we used a formula and a calculator to determine hc, computed altitude. Then I said, we use the difference between the altitude we calculated we should see, and the actual observed altitude, and we move our LOP the amount of that difference. In #7 we see an LOP is actually a segment of a huge circle of equal altitude. Closer to a stars GP means we observe a higher altitude, and further away, a lower one.
    OK. Wheres our LOP we need to move? Obviously it includes, passes through, the DR position we calculated hc for.
    Where is the center of a wheel? follow the spokes. If we calculate a spoke, azimuth, direction toward the GP of the star, our LOP is perpendicular, right angles, to that "spoke". And passes thru the DR.

    The formula is shown in a drawing attached, due to limitations of my keyboard.
     

    Attached Files:

  4. Yobarnacle
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    Yobarnacle Senior Member holding steady course

    Again, formula contains 3 sin and 3 cos. It contains inputs of L latitude (twice), and dec declination (once), and we input the hc (computed altitude) we calculated, twice. The result is a cos of the azimuth, the direction of the stars gp. We invert cos to change that result into an angle, a bearing. We plot an @ line thru our DR in that direction. We draw a perpendicular LOP across the @ line the appropriate distance closer to the stars GP or further away.

    Is this clear? or confusing?
     
  5. Yobarnacle
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    Yobarnacle Senior Member holding steady course

    Good idea. Print out copies of perpetual almanac, stuff into bottles and cast adrift. Pepper the seas with them. Then, any mariner, or even castaway, could fish one out, and calculate where he was.
    I personally volunteer to help empty the bottles, if it's good vintage and someone else is buying
     
  6. Yobarnacle
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    Yobarnacle Senior Member holding steady course

    The great advantage of using these two formulas and an inexpensive batteryless breastpocket calculator is, you can generate your own sight reduction table. With but a single tabulatiom. Exactly on your DR.
    No interpolation or extrapolation. Simple, neat, and light weight. Glue 2 formulas on back of calculator or memorize. If you use them frequently, they'll get thoroughly imbedded and you'll never forget them. So, my suggestion is practice, practice, practice.
     
  7. BATAAN
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    BATAAN Senior Member

    Excellent trick!
     
  8. Yobarnacle
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    Yobarnacle Senior Member holding steady course

    You can write out the formula as a sort of flow chart. A list of buttons to push in correct order, similar to the break down I provided for the first formula.
    Anyway.
    An LOP isn't a position. Needs 2 or more LOPs to get a "fix" on your position. Right angle LOPs are best but extremely rare. Normally, we use 3 stars to generate 3 LOPs. Where they cross, is our fix.
    I'll share a secret. In half a century since I began studying the sextant, I have never shot a "cartwheel". I'm real skeptical of those who claim they have, or can. A cartwheel would be where 3 LOPs crossed at a single point. Nah! Almost always, and for me always, they define a small triangle where they meet. A cocked hat. Generally you can assume your position is centered in the "cocked hat". There are times it's prudent to expect you are closer to a danger, such as a shoal, and navigate accordingly. So, you mark your position on the cocked hat closest to the danger.

    next running fixes, jump in with a comment anytime Gonzo
     
  9. BATAAN
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    BATAAN Senior Member

    Best book ever on practical piloting tricks and tips, gleaned from tug skippers, schoonermen and more.
    Higgins Industries boat operator school, 1943.
     

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  10. Yobarnacle
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    Yobarnacle Senior Member holding steady course

    I want to share a bit of "wisdom" with you gentlemen. I have a greybeard so supposedly wise, huh?
    Ships aren't democracies, but use your authority sparingly. A team leader needs to be a team builder, and a crew is a team, or should be. That's not news. All of you know how to gain co-operation.

    Here is where you should be hardnosed. The word "FOG". Forbid mentioning it on board. I have a cigar box on the bridge with a slot in top. Watch standers are fined a quarter if they use the 3 letter word. It better never be logged, unless tied to a dock, and even then I don't want to read an entry of FOG.
    Why? Because a vessel must proceed at a safe speed at all times, defined as the ability to stop within one half the distance of visibility. That's the law.

    If you have a collision, and your log says you were running in fog, and the other vessel log says they were running in haze, or restricted visibility, YOU are culpable. You are at fault in admiralty court.

    Forbid speaking the word. Even if all your navigators agree it was hazy, one deckhand testifying he overheard the bosn and 3rd officer talking about how foggy it is, will sink your career. Your license is toilet paper. Hear and tremble! Outlaw damned FOG.
     
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  11. SheetWise
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    SheetWise All Beach -- No Water.

    Yobarnacle,

    Regarding the characters you're having problems mapping to your keyboard, you can enter the character code on your keypad while holding the ALT key down, and when you release the ALT key, it will appear ... but there is an easier way if you're working in Windows® ...

    Open, Programs --> Accessories --> System Tools --> Character Map

    With the character map open, you can simply drag the character you want into most applications. It's handy to have on the desktop.©

    λ
     
  12. Yobarnacle
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    Yobarnacle Senior Member holding steady course

    Thanks, I'll try that. I'm a terrible typist. Fast, one finger, clumsy, terrible typist. I'll try to learn. :)
     
  13. Yobarnacle
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    Yobarnacle Senior Member holding steady course

    Lesson #9 The running fix

    This is an important navigation tactic.
    Often you have sporadic opportunity to get a clear sight. As Gonzo posted earlier in thread, you can take the middle time between a morning and afternoon sight that are equal altitude and determine when LAN was.
    When you got that morning shot of the sun, work it up as an LOP, a sun line. In the afternoon, even if the altitude isn't the same, if the squalls pass and you get another sun line, advance the morning LOP along your course a distance your speed would carry you in the time between the 2 sights, and the LOPs cross for a "running" fix.
    Other LOPs can make running fixes.
    You are navigating to clear a shoal and your fathometer begins reading depths. Prior you were off soundings, too deep to read. Ideally the fathom curves will parallel your course if you are skirting the shoal. Or perhaps you are headed in and crossing the continental shelf. At any rate, that 10 fathom line, or what ever depth your are in is an LOP. You are somewhere on that line. Advance an earlier LOp nearly as possible right angles to the fathom curve, and you have a running fix.
    A bearing on a headland or a lighthouse is a LOP. Advance an earlier LOP for a running fix. Plenty of variety in LOPs. Hopefully you catch the drift.

    Final lesson next GREAT CIRCLES
     
  14. Yobarnacle
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    Yobarnacle Senior Member holding steady course

    Lesson #10
    Finally
    Great Circle sailing. Everybody knows what a rhumb line is? It's a compass course. On the equator, steering due east or west, is a great circle course. Everywhere on the planet, steering due north or south is a great circle course. All other courses of constant heading are rhumb lines.
    Who cares?
    Well a voyage plan is an important tool. You plan to take advantage of fair winds and convenient currents, avoid areas notorious for bad weather, certainly avoid contrary currents, avoid crossing into unfriendly territorial waters, avoid reefs and shoals. Schedule fueling/watering ports enroute, and pick the shortest route taking these other factors and more in consideration.
    The most direct route is a great circle.
    If you steered northeast and didn't run into land anywhere, you'd spiral around the globe in a tighter and tighter spiral untill you arrived at north pole. From there all courses are south. Quicker route to north pole is North. North is a great circle of the earth and northeast a rhumb line, you see?

    If you take that first formula and change a few names it calculate great circle distance. The second formula calculates first course leg of the great circle route. You just substitute starting latitude for L and ending latitude for dec. You subtract your longitude from longitude of destination to get difference in longitude, Difference in longitude takes the place of LHA in first formula.
    Once you calculate great circle distance with first formula, that distance plugs in where hc (computed altitude) is in second formula. To find last course leg, run the formula again, exchanging start position and destination. The course calculated would be first leg of return trip. Reciprocal, that's 180 degrees around, would be last leg of initial voyage. You check this to make sure your final approach isn't cross land or shoals. Intermediate legs are calculated from your new position anywhere enroute. Just treat as a new great circle route with same destination.
    Clear? or confusing?
     

  15. Yobarnacle
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    Yobarnacle Senior Member holding steady course

    Hope y'all find these two formula and methods usefull. Thanks for your posts and votes. Digress if you want, hijack the thread, I like navigation, obvious, huh?
     
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