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Thread: km/hr or kn?

  1. #31

    Re: km/hr or kn?

    I don't think gps is that accurate, mine tells me the height = 26 foot.
    How can that be when the boat is at sea level.
    A marriage licence should be like your fishing licence!
    Expires every year and you get a 3 day pass when you go interstate.

  2. #32

    Re: km/hr or kn?

    Have a read of your Gps/sounder setup instructions, some where you will be able to fix that..

  3. #33

    Re: km/hr or kn?

    Thanks Predator, think I will go find me manual.
    A marriage licence should be like your fishing licence!
    Expires every year and you get a 3 day pass when you go interstate.

  4. #34

    Re: km/hr or kn?

    Quote Originally Posted by Roughasguts
    I don't think gps is that accurate, mine tells me the height = 26 foot.
    How can that be when the boat is at sea level.
    GPS vertical accuracy is quite different to horizontal accuracy and the height a GPS determines/computes is effectively not directly related to sea level. SPS vertical accuracy is in the order of 2-2.5 times less accurate than horizontal.

    A GPS height initially relates to the ellipsoid, which is a mathematically defined shape of the earth. To determine heights related to sea level then an additional geoid model has to be used. Some GPS receivers might only display ellipsoid heights, others might also display orthometric (seal-level type) heights but the sea-level height is only as good as the accuracy of the geoid model and since most GPS receivers that do this have a world wide geoid model it's not all that accurate in itself.

    Regards, Kerry.


  5. #35

    Re: km/hr or kn?

    Quote Originally Posted by Kerry
    GPS vertical accuracy is quite different to horizontal accuracy and the height a GPS determines/computes is effectively not directly related to sea level. SPS vertical accuracy is in the order of 2-2.5 times less accurate than horizontal.

    A GPS height initially relates to the ellipsoid, which is a mathematically defined shape of the earth. To determine heights related to sea level then an additional geoid model has to be used. Some GPS receivers might only display ellipsoid heights, others might also display orthometric (seal-level type) heights but the sea-level height is only as good as the accuracy of the geoid model and since most GPS receivers that do this have a world wide geoid model it's not all that accurate in itself. #

    Regards, Kerry.
    #
    wow, try saying that after a couple of bourbons

    for interest sake, in the world of offshore navigation, spherical trigonometry and celestial bodies, the earth is referred to as an 'oblate spheroid'.
    just thought I'd throw that in

    regards

  6. #36

    Re: km/hr or kn?

    Thanks Kerry, Electronic gadgets aren't my thing, I get lost after congratulations on your purchase.

    It's then I realise I will never use the gadget to it's full potential.
    A marriage licence should be like your fishing licence!
    Expires every year and you get a 3 day pass when you go interstate.

  7. #37

    Re: km/hr or kn?

    I'm staying away from this one.

  8. #38

    Re: km/hr or kn?

    Quote Originally Posted by gelsec
    for interest sake, in the world of offshore navigation, spherical trigonometry and celestial bodies, the earth is referred to as an 'oblate spheroid'.
    just thought I'd throw that in #
    "Oblate Spheroid"? Yes, but which one?

  9. #39

    Re: km/hr or kn?

    Quote Originally Posted by Kerry
    [quote author=gelsec link=1163963852/30#34 date=1164153991]
    for interest sake, in the world of offshore navigation, spherical trigonometry and celestial bodies, the earth is referred to as an 'oblate spheroid'.
    just thought I'd throw that in #
    "Oblate Spheroid"? Yes, but which one? #
    [/quote]

    the kind the earth is? flattened at the poles.

    not so apparent if using mercator projection charts in latitudes less than 60 degrees.
    if you wish to navigate in higher latitudes, not advised unless you have a good reason (some great circle routes do go to 65-70 tho), gnomic projection charts are used, and the earth's shape becomes more apparent.

    this is for maritime navigation, not familiar with aviation navigation, so can't comment, and not a wizz on GPS techs.

  10. #40

    Re: km/hr or kn?

    Next question :are knotts faster then Km/h?



    Ahoj---its not me)

  11. #41

    Re: km/hr or kn?

    Use kilometers they tick over faster, and whats this oblate hemoroid stuff!! the earth is flat.
    Well at least it soon will be, just got to speed it up a bit and get that centrifical force going harder and she will flatten out even more at the poles.
    Gonna have to watch that sharp ridge at the equator, in a boat though.
    A marriage licence should be like your fishing licence!
    Expires every year and you get a 3 day pass when you go interstate.

  12. #42

    Re: km/hr or kn?

    Quote Originally Posted by Roughasguts
    Use kilometers they tick over faster, and whats this oblate hemoroid stuff!! the earth is flat.
    Well at least it soon will be, just got to speed it up a bit and get that centrifucal force going harder and she will flatten out even more at the poles.
    Gonna have to watch that sharp ridge at the equator, in a boat though.


    actually you might be closer than you think, it's not centrifugal force we have to worry about!
    it's the magnetic poles reversing, North moves to South, or no poles, no lines of magnetic force.
    the earth's core is running out of magnetism, and the scientists aren't quite sure what will happen when it does.

    of course it's a lot more complicated, but it could happen in our lifetime or maybe the next, a big grey area.

    now that I brought it up, I'm sure someone will enlighten us or debunk the theory.

    what's the website of the flat earth society?

  13. #43

    Re: km/hr or kn?

    Hmmm interesting losing our magnatism.
    You think it's from mining all those billions of tonnes of iron ore, then re-distributing it in other parts of the world.

    Think we better start looking for another planet to live, this ones........ just about, F***** ah, finished,. We could then sap the earth of all it's goods and when were done, dump all our waste here.
    Bloody hell even killing off the magnetic field, were pretty good.
    A marriage licence should be like your fishing licence!
    Expires every year and you get a 3 day pass when you go interstate.

  14. #44

    Re: km/hr or kn?

    Oh yeah the North Pole has been on the move for many years, gradually and progressively heading west/north-west. Even on a daily basis the north pole dances around quite a bit.

    As for the poles switching there is evidence that this has occured?

    ....and whats this oblate hemoroid stuff!! the earth is flat.
    That is slightly flat, top and bottom Oblate Spheroid? flash sounding name for what most simply call the datum

    Flat but it can't be flat? Like where does all the water go when the tides out

    Regards, Kerry.

  15. #45

    Re: km/hr or kn?

    Oh yeah thanks Kerry, I remember reading the magnetic variation changes on me charts, they don't stay fixed any more they do move over time.

    I think since I started flying the magnetic variation has moved 0.5 degree which sound like nothing. But if you use the 1 in 60 dead rechoning stuff thats 0.5 Nm off track or course, in a 60 mile trip.

    Recipe for disaster with old charts.
    A marriage licence should be like your fishing licence!
    Expires every year and you get a 3 day pass when you go interstate.

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