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    Re: HO 249 assume position
    From: Murray Buckman
    Date: 2025 Oct 27, 11:54 -0700

    While agreeing with Tibor's comments technically, I offer a different view of the practical approach if the intended exercise is to use pencil and paper and simulate a small boat.

    This may be your pupose.  My comments are based on practice in small boats, and often in cloudy locations, where the ease of a shot and visibility of the star is not always guaranteed using a timed sight approach.  Take the sights as quickly as the stars and visibility allow, but slowly enough to have confidence in identification of the star and the quality of the sight.  The resulting time between sights is what it is.

    The Air Tables were popular for small boat navigation before satelite navigation tools cam along, and were all I ever used.  In my very early navigation days I did not use a calculator either.  When using the tables, rather than a calculator or program, yes on multiple APs.  Having calculated GHA Aries for each star in the sight set, calculate a chosen longitude for each backward from the nearest whole degree of LHA Aries, such that the chosen longitude (close to your estimated longitude) plus GHA Aries equals a whole degree of LHA Aries.  Chose the nearest whole degree of latitude.  That makes the rest of the sight reduction as easy as possible on pencil and paper.  Three or four star sights can then be calculated in columns at the same time, with the data pulled from the tables for each as you go, rather than jumping back to the tables for each separate calculation.

    Depending on the time between sights and the speed of the boat (in my case) the movement of the boat can be ignored up to a point.  As I have always sailed relatively slow boats (when compared to a ship, aircraft, or some of the very fast modern racing sailboats, I have always ignored movement.

    Of course for land-based observations and a clear sky my comments about the actual sight-taking are irrelevant.  But using APs to get to a whole degree of LHA Aries still applies to a pencils and paper approach to the Air Tables.

    Murray

        

       
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