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D. Lat and D. Long

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  • D. Lat and D. Long

    Hi all,

    I started college 2 weeks ago. We've since been given an introduction to latitude/longitude etc, and we were given a few questions on working out the difference between two latitudes or longitudes etc...unfortunately it seemed to go over my head and I would appreciate it if anyone could help me understand how I go about working out these:

    1) Calculate the D.Lat between the following positions:
    (a) A port in Latitude 22? 30' N and a port in Latitude 10? 15' S.

    2) Calculate the D.Long between the following positions:
    (a) A ship in Longitude 20? 17' W and a port in Longitude 10? 43' E.

    The main thing that threw me was when two latitudes were in the same hemisphere and having to subtract them if I remember rightly...either way, as I said, I would appreciate it if someone could explain it briefly to me again!

    Thanks in advance,

    Jack.

  • #2
    In example one, put yourself on that ship. You're in the northern hemisphere. The port you want is in the southern hemisphere. You're 22? 30' above the equator. The port is 10? 15' below the equator. So you add the two. You're heading south, so your D'Lat is 32? 45' S.

    Example two, pretty much the same but the ship is 20? 17' W of the Greenwich meridian, the port is 10? 43' E of the Greenwich Meridian. Add the two, and the direction is E.

    If they're in the same hemisphere, subtract the smaller one from the bigger one and apply the correct direction.

    The only time things really change is if you're round the back of the world. In that case, add the two and then take that figure from 360 to get your D'Long since it's a lot quicker to nip round the date line than it is to go via Greenwich,
    sigpic
    Hello! I'm Chris. I'm away a lot so I'm sorry if it takes me a while to reply to messages, but I promise I'll get back to everyone. If it's urgent, please email me directly at [email protected].

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    • #3
      I've just spent the day doing these, safe to say I now get them!

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      • #4
        Correct me if i'm wrong, but dont you also times the result by 60 minutes? So you get something like 4389'N (thats not the answer btw), I've not got my notes to hand because Im somwhere in the atlantic off the coast of Africa but I'm sure thats the way we were taught.

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        • #5
          Hi all, thanks for your help.

          RNR: This is what confused me. Our lecturer was telling us that we couldn't just subtract as we would 'normally', and from then on it got confusing.

          Jack.

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          • #6
            I just do it all on my calculator, makes things much easier.

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            • #7
              RNR is quite right, forgot about that bit!
              sigpic
              Hello! I'm Chris. I'm away a lot so I'm sorry if it takes me a while to reply to messages, but I promise I'll get back to everyone. If it's urgent, please email me directly at [email protected].

              Need books, Flip Cards or chartwork instruments? Visit SailorShop.co.uk!

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              • #8
                If in doubt, draw a picture. It helps make it so much clearer.

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                • #9
                  Originally posted by AncientMariner View Post
                  If in doubt, draw a picture. It helps make it so much clearer.
                  My sailings and Cel Nav exam papers were covered in drawings, it's the only way to ensure you're concept is clear.

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