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    Re: GPS jamming concerns
    From: Mark Coady
    Date: 2016 Aug 10, 19:05 -0700

    Frank, 

    Your chart explanation brought me back to another question I was pondering and saving. I attached a jpg of an 1847 chart of fisher's island...it set me to thinking... considering this has been my home port stomping ground, off and on...since I was a child....I looked at this and was stunned to see how well defined it seemed to be...and presumably similarly accurate?  I hope to print it on tracing paper and overlay it on a similarly scaled modern chart at some point. I should be able to fudge scales using the legend.

    In the mid 1800's.. how much of this might have been astronomical vs surface trigonometry and surveying. How to plot a detailed depth or underwater obstruction from a floating vessel other then triangulation? I have used that with great success locating wrecks.  I mean land is a challenge enough, but reefs and shoals, depths, over water... etc... must have posed quite a challenge.

     My guess is they didn't have any batteries for their GPS...



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