NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Logs vs Knotmeters
From: Alexandre Eremenko
Date: 2008 Mar 29, 22:39 -0400
From: Alexandre Eremenko
Date: 2008 Mar 29, 22:39 -0400
Dear Lu, > I suspect patent logs (sucn > as Massey's or Walkers) were used > strictly for distance measurement, > since distance traveled is needed for DR navigation, All logs described in Leckey (1919) measure DISTANCE. But not "because distance traveled is needed for DR"!) Just because they did not know how to measure speed directly. A (patent or taffrail) log is used to measure the distance over a short period of time. Then this measured distance is divided by the time to deduce the speed. Then when doing DR the speed in converted to the traveled distance. There are many reasons why they could not use a taffrail (or earlier) lots continuously. The main reason is quick wear. According to Lecky, wear of the gear was a major problem, even with short time ise of lots. Leckey also mentions propeller or paddle revolutions on steamships to measure speed and says that this is not worse than any patent-log. > "did people switch back to speed measurements before > dropping DR altogether" Yes. Most of the XX century (definitely from 1950-s till the time of GPS) they used pressure logs that show SPEED rather than distance. And they did dead reconning until GPS times. I used to have a Russian 1970-s book on dead reconing. It was mandatory on Russian ships at that time. The logs were pressure logs measuring both speed and the distance. Taffrail logs were still used as a backup. Alex. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---