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    Re: Traditional navigation by slide rule
    From: Bob Goethe
    Date: 2016 Nov 12, 00:43 -0800


    These different flight computers you have are *quite* interesting.  

    In the sailing circles I run in (where almost nobody races), very few people even do time/speed/distance calculations, and an even smaller number do current vectors.  Sailboats are forever having speed variations as well as course variations due to differences in wind direction/velocity.  Of course, given the general principle that no matter where you want to go, the wind will be against you at least part of the time....this means that you are involved in tack navigation.  To really stay in control of time/speed/distance, currents and corrections almost requires that you have somebody on board who is a dedicated navigator.  I think some of these sorts of calculations are easier, and hence more common, among power boaters, who are in a better position to manage consistent course and speed settings.

    Prior to this, my only use of a slide rule on the water was for sight reduction of celestial sights, plus great circle calculations.  I am looking forward to trying to make some use of a slide rule in British Columbia coastal navigation, where currents play a significant role.

    Canada's hydrographic agency has released a wonderful tide atlas of the BC coast, so (if you learn to use it properly) you can know the set and drift for a given location, on an hour-by-hour basis.

    I think part of the issue is that things like the flight computers you illustrated are not common in the sailing world.  It is simply hard to carry out the computations you need quickly enough to make it worthwhile to even attempt them.  People all do current-vector diagrams to get their navigational certification from Sail Canada (previously called the Canadian Yachting Association) and then they never touch them again.

    If I can get on top of the fabrication of the 10" rule, I may create a simplified design and build a shirt pocket rule specifically optimized for solving the current triangle and doing speed/time/distance, for the helmsman to use without leaving the cockpit.


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