Thomson plumb bob

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The Thomson plumb machine is a mechanical plumbing device invented by William Thomson, 1st Baron Kelvin in 1876 ​​and patented in Great Britain, for determining the water depth of a ship in motion.

functionality

Thomson's plumb bob is a wire plumb line whose plumb line runs off the drum of the plumb bob when the ship is at full speed. On the actual solder body there is a cylindrical glass tube that is closed at the top but open at the bottom. There is a coating of chromic acid silver ( silver chromate ) on the inner wall of the glass cylinder . This coating changes color when it comes into contact with seawater. The water compresses the air in the glass cylinder according to the maximum water depth reached. The depth is recorded from the water pressure which increases with it. The path that is discolored in the glass cylinder is then a measure of the water depth reached. Tests did not show any influence on the measurement result, regardless of whether the plumb line sinks vertically or at an acute angle. The plumb bob works optimally up to a speed of 11  knots and a water depth of up to 200 meters.

operation area

The Thomson plumb bob could be found on larger merchant ships until the 1920s. The system was used on research vessels and cable layers in the preparation and laying of deep-sea telegraph cables.

Components

The Thomson soldering machine consists of a metal support frame for the wire drum. The solder wire is located on this drum. A crank is attached to the side of the wire drum to retrieve the solder. A circular scale with a pointer to indicate the elapsed wire length is attached to the support frame. The pointer is connected to the wire drum via an adjusted gear system. The solder body with the recess for the solder feed is attached to the end of the solder wire . The glass cylinder protected by a brass sleeve is located a little higher on the solder wire.

literature

  • U. Scharnow: Lexicon of seafaring . various years, transpress VEB Verlag für Verkehrwesen Berlin, ISBN 3-344-00190-6 .
  • Martin Berger: Hundred years of technical navigation. In: Paul Schroedter (Ed.): 100 years of shipping - shipbuilding - ports: Hansa 1864–1964. Schroedter, Hamburg 1964