Yesterday we asked, what is a “pitometer”  and where did the term originate?

Also known as pit logs pitometers are devices used to measure a ship’s speed relative to the water. They are used on both surface ships and submarines. Data from the pitometer log is usually fed directly into the ship’s navigation system.

Pitometers date back to days of sail when sailors tossed a log attached to rope knotted at regular intervals off the stern of a ship. The sailors would count the number of knots that passed through their hands in a given period of time. Today sailors still use the unit of knots to express a ship’s speed. The speed of the ship was needed to navigate the ship using dead reckoning, which was standard practice in the days before modern navigation instruments like GPS. During World War II, pitometer logs were often interfaced directly into warship fire control systems. This interface was necessary to allow gunnery and torpedo fire control systems to automatically track tar.