Ship's depth gauge

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Ship's depth gauge
Early 19th Century

Provenance unknown
Museum number Temp. Number 11,948

This instrument for measuring the depth of water beneath a ship was commonly known as Massey's sounding fly. The sounding fly was invented by Edward Massey at the beginning of the 19th Century. The gauge would have been attached to a very long lead weight on a very long rope. The device was set to zero and dropped overboatd the ship. The rotating propellors drive the scale which is graduated in fathoms until the weight hits the bottom. While the instrument is being pulled back up, the pressure of the water depresses the disc on top of the gauge, which stops the rotator from moving. It is therefore not necessary to feel the instrument touch the bottom, since it will only record the depth as it descends.

Ship's depth gauge
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