““At sea, navigators need to know how fast their vessel is moving through the water. Prior to the GPS, this was done with a nautical instrument known as a log. The devise that was attached to the handrail around the stern of the ship was known as a taffrail log. These instruments consisted of an impeller, or rotator made of brass, usually with four blades, a reading dial accurately calibrated, and a line that connected the two parts. As the impeller was dragged through the sea it rotated, turning the dial that registered the ships speed in knots, which equal one nautical mile per hour. The taffrail log usually registered the ships speed in knots, and tenths of a knot….. The earliest known taffrail log, also known as patent log, was designed in 1688 by an Englishman, Humphry Cole. Taffrail logs were later manufactured by the Lionel Corporation, perhaps better known for the manufacturing of model trains. They remained in business from 1900 to 1995, producing “Taffrail Logs” for the US Navy during World War II.””
