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    Re: Logs vs Knotmeters
    From: Lu Abel
    Date: 2008 Mar 29, 18:57 -0700

    Alexandre E Eremenko wrote:
    >> Somewhere along the line, patent logs
    >> (such as the Walker log) were
    >> invented and distance was measured
    >> directly by trailing the log's
    >> spinner.   When?
    >>
    >
    > The first spinning log was apparently invented by
    > Edward Massey in 1802, it was in general use by 1836
    > and used until 1961. It was improved by
    > Alexander Bain in 1946.
    > First Walker's log was invented in 1861.
    > All these early logs had a disadvantage that the dial
    > was close to the screw, so one had to pull the log out
    > to see the traveled distance.
    >
    > Then in 1878 the same Walker invented the "modern" version
    > with the dial attached to the taffrail.
    > All these logs indicate the distance traveled,
    > rather than speed, and one has to use a clock with them.
    >
    Alexandre:
    
    This last sentence relates to my question.   I suspect patent logs (sucn
    as Massey's or Walkers) were used strictly for distance measurement,
    since distance traveled is needed for DR navigation, because ships speed
    was available via a engine RPM-to-speed table which was very common on
    ships a century ago.
    
    You helped answer the most important part of my question -- people
    started using direct-reading logs (from which DR could be done) early in
    the 19th century.  I guess that the second question might be more
    clearly worded "did people switch back to speed measurements before
    dropping DR altogether"
    
    Lu
    
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