Boston Public Library

Atlantic Neptune Part 1 – Item 20 of 23

Greg Germain, Common log reproduction, Marblehead, MA, 1997. Mahogany, pine, natural fiber line.
Courtesy Naval History & Heritage Command Detachment Boston.
First used by mariners in the 15th century, the common or chip log is a device which measures the speed of a ship through water, or the distance the ship has traveled in a given time. A 28-second sand glass was used in conjunction with the log, to record the speed. The log, or chip – a flat piece of board – was fastened to a long line, which was divided into uniform spaces called knots, and was wound onto a reel. Knots were spaced every 48 feet (8 fathoms) along the line, and were proportional to the number of times 28-second intervals occurred in an hour. This method of measuring speed would have been used by the British navigating to the North American empire, and was used until the early 20th century.