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    Re: The Great Circle Challenge
    From: Hanno Ix
    Date: 2014 Dec 27, 18:01 -0800
    Hi, Francis -

    now, if you hadn't access to this site here - out on the boat all by yourself -
    how would you know you made an error?

    I assume you would established some redundancy in your routines.
    If my life depended on the accuracy of sight reduction I would not sail without one.

    Repeating the same method would not be advisable - not areal redundancy.
    One obvious one would be two people doing two sight reductions
    independently and compare. But even in this case questions arise:
    should they use the same method or different ones? What makes for a better
    error checking?

    BTW: Did the Royal Navy apply redundancy? If so, in what way?
    Numerous examples presented in the classical literature by expert authors
    come up with the wrong answers. You know, complicated sign rules, logarithmic
    calculations, multiple tables etc. plus the appearent absence of redundancy 
    make an excellent recipe for committing errors.

    OK, then: What is a good sequence of redundant sight reduction?
    I think, one may start with the assumption the first one was wrong and then proves
    this assumption of an error being wrong.

    Would you use the Bygrave first and then check with a BN?


    On Sat, Dec 27, 2014 at 4:21 AM, Francis Upchurch <NoReply_Upchurch@fer3.com> wrote:

    Apologies I made an error on the Bygrave. Several check repeats now give 4059 nm distance. 25˚55’ course.



    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Francis Upchurch
    Sent: 27 December 2014 09:41
    To: francisupchurch---.com
    Subject: [NavList] Re: The Great Circle Challenge


    Merry Xmas Navlist folk.

    The following probably adversely affected by seasonal excesses.

    Bygrave: Course 25˚55’, dist 4063nm. Took 2 minutes. (substitute Dec= arrival lat, LHA (t) = difference longitude.)

    Brown-Nassau prototype: Course 26˚. Dist 4070nm. Took 1min 30 secs approx.

    What is the best ,correct answer?

    Best wishes,

    Francis Upchurch


    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of David Pike
    Sent: 26 December 2014 16:21
    To: francisupchurch---.com
    Subject: [NavList] The Great Circle Challenge



    The Great Circle Challenge




    Clearly, from recent posts, we all have a favoured way of solving great circle sailings (which we’ll probably never use for real).  Let’s put them to the test by trying something a bit more complicated like a southern to northern hemisphere crossing combined with a crossing of 180degrees E/W.  How about emulating Captain Cook by travelling from Cook Strait (CS), New Zealand to Waimea Bay (WB), Kauai, Hawaii?  Cook followed the pretty route, but we’ll go direct by great circle.  The coordinates are CS 41d 30’S, 174d30’E to WB 21d57’N, 159d 40’W.  Use your favourite method and report back on your answer, the time it took you, and any difficulties encountered.


    I’ll stick with the diagram method, because at least I’ll know what I’m trying to prove, and I won’t have as many rules to remember and apply which might or might not work.  Dave


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