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    Re: I knew where we were, but where are we now?
    From: George Huxtable
    Date: 2006 Jun 26, 22:46 +0100

    Recently, Peter Fogg has been particularly free with his words of
    advice.
    
    He responded to Lu Abel's correct statement-
    
    | > If you look at Chapter 24 of Bowditch as mentioned in my previous
    post,
    | > the most accurate sailing is a Mercator sailing.
    | > Mercator Sailings rely on Table 6 of Bowditch, Meridional Parts.
    
    with
    
    | Almost correct. The most accurate uses tables of meridional parts
    AND
    | meridional distances.
    
    I ask Peter to inform us about this "Table of meridional distances",
    that he regards as so essential. Where are we to find it, and what is
    done with it, under what circumstances?
    
    | Having said that, if Guy wants to concentrate on one calculation
    method,
    | then he could do worse than settle on Middle Latitude.
    
    In certain limited circumstances, not specified by Peter, yes. In many
    other situations, no. In general, the procedure that gives precise
    answer under all circumstances is the Mercator sailing method, using
    meridional parts.
    
    |But nobody has
    | mentioned the other quick and reliable method that is accurate
    enough for
    | practical purposes, and offers other advantages that calculation
    methods
    | cannot.
    |
    | Plot it. On the chart if you must (barbarian). Preferably on the
    succession
    | of plotting sheets that track your progress. The big advantage is
    that it
    | provides a picture (quite literally) thus showing you just where you
    are in
    | a spatial two-dimensional sense: much more valuable than numbers
    that you
    | are then most likely to plot onto paper anyway. I think of plotting
    as a
    | primary method and calculation as a back-up or check method.
    
    It depends entirely what sort of sailing you are doing. In the sort of
    sailing that I do (and Peter does too, I bet) there's no call for any
    Mercator calculation. Middle latitude is perfectly adequate, as is
    plotting on a chart. But if he travelling great distances (as some do)
    on ocean passages spanning a wide range of latitudes, he would be
    unlikely
    to find his simple plotting techniques practical. So in advocating a
    certain method he should make it clear what its limitations are.
    "Accurate enough for practical purposes", says Peter. But accurate
    enough only for some practical purposes, and not for others. I ask him
    to tell us what is the longest passage he has made, using the
    techniques he advocates.
    
    George.
    
    contact George Huxtable at george@huxtable.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    
    
    

       
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