What does "engineering accuracy" mean to you?

Discussion in 'Hydrodynamics and Aerodynamics' started by Leo Lazauskas, Feb 4, 2013.

  1. Number4

    Number4 Previous Member

    Yes Michael, it is sad no one navigates properly any more.
    GPS and computers make one so lazy.
    I love maps and compasses, I was lucky to have had very good instructors.
    One day when someone pulls the plug on the GPS system alot of people will be totally lost.
     
  2. Leo Lazauskas
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    Leo Lazauskas Senior Member

    I can't remember what method jesuits tried to beat into me when I was at
    school, but I like the simplicity of the techniques described here.

    It makes me feel for J.H. Michell who, in 1898, took 3 months to evaluate his
    (quintuple) wave resistance integral to 3 sig figures for one Froude number.
     
  3. Number4

    Number4 Previous Member

    Hi Slavi,
    The wizz wheel is a very beautiful thing.
    http://www.youtube.com/watch?v=sS6GMTAKerA
    It sits in the palm of your hand and it can work out everything you need to know when flying a light aircraft.

    Must go it is time to watch the Azurri beat the Scots at rugby.

    Cheers,
    Adam
     
  4. michael pierzga
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    michael pierzga Senior Member

    This lack of chart work hurts the crew. A typical Transatlantic ,when navigating with a sextant, required the whole crew to be involved with recording sun elevations and carefully updating your DR. Now they all sit around bored, eat and sleep . Inshore its even worse..they never know the location of the boat... as in 12 miles south of Fastnet Rock , they never learn topographic details as in ..what is the name of that tall mountain or island , and they never learn to calibrate their eyes for things like distance off a breaker. Even buoy flash sequences seem to be black art .

    Modern sailing is boring.

    About the only excitement these days is the onerous VTS reporting schemes that keep you on the VHF non stop answering the ever present THIS IS OPERATION SOMETHING calling ship in position... seen any bad guys ? report all suspicious activeties to Central Command stuff. . You hear some mighty funny exchanges between the shore operator and the watchman.

    Blacked out high speed Italian patrol boats off the Albanian Coast are also exciting when they get on your transom.
     
  5. tom28571
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    tom28571 Senior Member

    Very nice, Latestarter. Problem is, I'm an earlystarter and will not remember this tomorrow.
     
  6. latestarter
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    latestarter Senior Member

    You should write it down on a piece of paper or tie a knot in something :D
     
  7. tom28571
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    tom28571 Senior Member

    Sure.
    Now, what is that string doing there?
     
  8. philSweet
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    philSweet Senior Member

    It's good that navigation found it's way into this thread. Navigation has motivated many advances in engineering accuracy. Clocks for longitude, Cartography advancements, celestial navigation instrument manufacturing including telescopes for producing the reference tables.

    Inertial guidance IMU's required several orders of magnitude improvements in multiple fields. Gravity was measured to about 60 significant digits (binary) back in the fifties. The first lunar hard landing was quite a feat of navigation. They apparently used the IMU's telemetry to measure the distance to the moon, a poorly known quantity at launch.

    The surveyors who managed to get long tunnels under big mountains to meet up in the middle have always impressed me. Some had to used 1000 points of reference all triangulated in three dimensions until the answers converged.

    The original survey of Mt Everest was correct to within 30 feet elevation. Beginning in 1802, it had taken 45 years to work a 7.5 mile base line on the east coast of India to the foothills of the Himalayas. Towers were built in the jungle to get above the canopy. From the foothills, they took some very long shots of several Nepalese peaks. In 1847, they couldn't accurately account for the index of atmospheric refraction at high altitudes. By 1856, they could and that's when the height of 29002 feet was published for the peak we now call Everest. It is currently listed as 29035 feet. The snow cap is 30-60 feet thick.

    The Great Trigonometric Survey of India is regarded as the most elaborate engineering calculation ever made prior to the computer era. It was not, however, a great example of job estimation. The East India Company estimated it would take five years to produce decent maps. It took 80.


    Ramsden's chain
    http://www.scienceandsociety.co.uk/results.asp?image=10280167&wwwflag=2&imagepos=6&screenwidth=1010
     
  9. Petros
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    Petros Senior Member

    when I was in high school in '74-77 and took an avid interest in mountaineering, they published height of Everest was 29,028 ft. I not surprised it changed some with new technology, I am surprised it did not change much. Consider also that earth crust changes due to plate shifting could have been much more than that over that time.
     
  10. DCockey
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    DCockey Senior Member

    Differences in measured elevation can also occur due to differences in the reference datum, and differences in these have probably contributed to the differences in the stated heights of Mt Everest. Terrestial elevations are typically referenced to a "reference ellipsoid" which is an idealized approximation of what the sea level would be if the oceans and atmosphere were still and had uniform properties. A number of different reference ellipsoids have been used. Actual sea level, the long term average height of the sea, at any location can differ from the reference ellipsoid.
     
  11. philSweet
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    philSweet Senior Member

    yup, but it is probably worth noting that the modern GPS is referenced first to a particular ellipsoid to get lat and long, and then a lookup table corrects this to the current geoid model for an altitude reference. The geoid is an equipotential surface that takes the variation in earth's mass density and mass distribution into account. It varies in height by as much as 106 meters from the ellipsoid.
     
  12. michael pierzga
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    michael pierzga Senior Member

    Still errors on charts. I often see discrepancies on Admiralty Charts when navigating to WGS 84 datum

    On the last cruise on the coast of Labrador I found many many inaccuracies when comparing GPS derives positions to charted location.

    Gps can be dangerous to navigators. The American Minesweeper presently on the reef evidently fell victim. to a gps electronic chart error.

    http://[​IMG] online photo storage
     
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  13. Submarine Tom

    Submarine Tom Previous Member

    What you have described is worst case.

    I have measured the earths surface movement by satellite to an accuracy of 2 cm horizontally and 0.5 cm vertically over a six month period.

    The more birds you have in good distribution across the sky for the longer time period, the more accuracy you can expect.

    But only fools navigate by GPS alone.

    BTW, I finally figured out what "engineered accuracy" means:

    Paying too dam much for most products.

    In other words: Marketing
     
  14. philSweet
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    philSweet Senior Member

    Hadn't though about marketing, but it is a good point. Why engineer something beyond the ability to make a useful marketing distinction? For the vast majority of stuff, there is no reason. You would need a corporate ethic to support that. Otherwise, you will just get pummeled for wasting time and resources. The social value of extra engineering effort would have to be promoted through regulation, such as the National Electric Code or NFPA.
     

  15. jehardiman
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    jehardiman Senior Member

    Yep, an electronic chart of a datum reference fixed in a 1834 RN survey is not very good. Cruising World a few years ago did a comparison of digital charts to reality. In the first world where regular surveys occured it was pretty good...but for much of the world, a digital is just a copy of the paper chart where the survey could be a century old. I call it screen fixation and it is one of the grimlins I constantly fight when training crews. Some times you need to open the window, and look, listen, and smell.
     
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