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    Re: Snellius Construction questions
    From: Nicol�s de Hilster
    Date: 2009 Jan 15, 09:04 +0100

    Richard M. Pisko wrote:
    > On Thu, 08 Jan 2009 14:03:52 -0700, Nicol�s de Hilster  
    >  wrote:
    >
    >   
    >> Later on I have been on projects where either station
    >> pointers or 'circle charts' were used to solve the position. A circle
    >> chart looks similar to a Decca chart, but now covered with circles that
    >> resemble the angles measured.
    >>     
    >
    > Are "circle charts" clear overlays for the coastal charts?  Do you center  
    > one on each reference landmark, and find the proper intersecting angle  
    > lines by eye?
    >
    > I have a couple of vague ideas of how that may work, but I could be off on  
    > the wrong track altogether.
    >   
    These circle charts were made on the job by the surveyor and showed only 
    what the navigator needed, in most cases that were a few known points, a 
    bit of coast line, an outline of the working area and of course the 
    circles. The charts were used for small area's of only a few kilometres 
    in diameter and usually made of paper (A1 or A0 size). The jobs where 
    they were used for were dredging and land reclamation jobs. The charts 
    were used to position the cutter suction dredges, which are almost 
    stationary vessels that move around using several anchors at long steel 
    cables, so hardly any speed involved. I just checked when I have last 
    seen these charts, which was only fifteen years ago in Nigeria (1994).
    
    > For a different approach, cheap station pointers might be made of three  
    > clear plastic disks, joined by a hollow rivet at the center, and graduated  
    > on the outer periphery in degrees.  Each disk would have one axial line  
    > pointing to its zero degree mark.
    >
    > However, I much prefer the workmanship in your real station pointers /  
    > three arm protractors.  Thanks for posting photographs of them.
    >
    >   
    You're welcome. Some more can be found (used, for sale) here: 
    http://www.santik.eu/instrument_ruler_pointer_en.htm
    As you can see on my web site one firm still produces plastic and metal 
    station pointers: Warren-Knight Instrument Company, see 
    http://www.warrenind.com/WKNavigation.html#Three Arm Protractors
    
    Nicol�s
    
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