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    Pointless? Optimisation - Intercept Plotting
    From: Michael Bradley
    Date: 2019 Feb 1, 11:25 -0800

    The attached plot shows a pair of LOPs from two notional intercept method sights reduced from the EP. They are  plotted on a print off of Frank Reed’s ( thanks Frank) universal plotting sheet set up for my local waters. They were plotted in a slightly novel way, optimised for the chosen plotting sheet.


    The Weems and Plath protractor 255 was chosen for this experiment because its moveable compass rose is close to one end. That makes it easy to use on a small plotting sheet.


    The protractor has additional parallel lines 2’ (of the plotting sheet Lat scale) apart drawn across its ‘bow’. (Lines 1’ apart makes things too busy for my taste). These parallel lines have been added to the protractor with an ultra fine permanent black marker pen. 


    For a Towards intercept the protractor is set to the Zn bearing at the ‘short’ end of the compass rose, marked ‘T’. For an Away intercept the protractor is set to the Zn angle at the ‘long’ end of the compass rose, marked ‘A’.

    Apply the protractor North arrow up to the plotting sheet, shimmy it about until the EP is the intercept distance from the bow edge, draw the LOP across the bow edge. That’s all. 


    Takes much longer to describe than it does to do. Takes the brain work out of calculating the LOP bearing. No stab marks from dividers. No construction line for the intercept itself. Quick, easy, and tidy fix plotting. Other plotters or parallel rules can be used similarly. The photos were taken from close up by phone and have minor parallax errors.

    Good navigating in 2019

    Michael Bradley






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