Log glass

The log glass was used in conjunction with a log and line in order to time the period during which the log line was allowed to unroll from the log reel and so estimate the ship's speed from the amount of line paid out. Usually this was for a period of up to half a minute. This brass log glass timed a period of 28 seconds and has the number 28 inscribed on both ends.

Object Details

ID: NAV0751
Collection: Astronomical and navigational instruments
Type: Log glass
Display location: Not on display
Creator: Unknown
Date made: 19th century; circa 1850
Credit: National Maritime Museum, Greenwich, London
Measurements: Overall: 85 mm; Diameter: 28 mm

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