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    Re: Azimith forumula for Great Circle sailings- having problems
    From: David Pike
    Date: 2014 Dec 24, 13:38 -0800


    Sam. I’ve just re-read your original question.  I would say you could do a lot worse than forgetting the formula for the moment and starting off with a simple diagram of the relationship between the two points on the surface of the earth and filling in the relevant values from their lat & longs, co-lats, ch-long etc. Then you know what you’re trying to find and how it all hangs together, as I’ve done in the diagram in my previous post. I’m assuming your LHA is what I would call difference in longitude between A and B.  You’ve not actually stated the longitude of A and B, but it looks as if B is roughly 106 nautical miles up the road from A (roads in the USA all running N/S or E/W).  If B is a little bit East of A the bearing is 004.  If it’s west of A, the bearing is 356.


    Looking at your figures, as a practical navigator, unless your doing this as a training exercise, I’d say forget great circles, rhumb lines, and lines of constant bearing.  Over 106nm they’re going to be within a 2B pencil width of each other.  A simple diagram would show you’ve gone 106 minutes of arc north and 10 minutes of arc east or west.  Using the 1 in 60 rule the bearing is 10/106 x 60 = 006 or 354.  It’s a couple of degrees off your figure, but it’s a good pilot or helmsman who can steer to 2 degrees.  


    Peter.  Where do I find this spreadsheet you’ve used?  Where does the 29/30 under lat and 147/911 come from?  Dave


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