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    Re: Sextant accuracy with short distance to horizon
    From: Dan Hogan
    Date: 2001 Jun 22, 9:57 AM

    On 22 Jun 2001, at 10:13, Steven Wepster wrote:
    
    My reply is based on experience. I am not a mathematician.
    
    > Dear Dan and others,
    >
    > In my opinion you have hit a problem that is specific to astro on
    > yachts: the very small height of eye. The problem is not so much that
    > it makes the horizon nearby. The normal dip table should be sufficient
    > as long as it lists your height of eye. I don't know for shure what
    > Peter and  Russell meant by 'dip short' tables: my 1981 Bowditch
    > Vol.II has a different table 14, but it has a table 22 'Dip of the Sea
    > Short of the Horizon'. This table gives the dip of objects _in front
    > of_ the horizon, so it should not be used for a normal altitude above
    > the horizon.
    
    Dip short tables ar for use when taking a sight SR/object distance and the
    horizon line you are using is short of the visible horizon.
    
    > More important: because your eyes are so low above the sea, it is most
    > of the time just plainly impossible to _see_ the horizon. The waves
    > get in between. When it is almost dead calm, there's no problem (but
    > it's not fun sailing then). You're lucky when the swell is running
    > high and regular, because then you can take a shot when you're at the
    > top.
    >
    > This raises another question: what is your height of eye at the top of
    > a wave? Do you have to add the wave height to your height above the
    > waterline of the vessel?
    
    Where on the swell you take the sight does not matter for HE calculation.
    What does matter is that you REALLY did take a horizon sight and not the
    top of a wave/swell.
    
    You can take a sight on land from any *level* surface of sufficient distance.
    I remember an "Aussie" list member that used the fence on his ranch in front
    of his porch.
    
    > In my opinion, the anser to that question is 'no'. I assume that waves
    > of appoximately the same height make up the horizon.
    >
    > _Steven
    
    
    Cheers
    -Dan-
    

       
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