Why is a ships speed measured in knots?
In the ancient times, the only way to measure ship speed was to throw a wood log into the water and observe how fast it moves away from the ship. This approximate method of ship speed measurement was called ‘Heaving the Log’ and was used until 1500-1600s when the ‘Chip Log’ method was invented (both methods probably invented by Dutch sailors.) The ‘Chip Log’ apparatus consisted of a small weighted wood panel that was attached to the reel of rope, and a time measuring device: a half-minute sand glass (as shown in image below to the right.)Chip Log Rope had knots tied at equal distances along the reel. Sailors would throw the wood panel into the sea, behind the ship, and the rope would start unwinding from the reel. The faster the ship was moving forward the faster the rope would unwind. By counting the number of knots that went overboard in a given time interval, measured by the sand glass, they could tell the ship’s speed. In fact that is the origin of the nautical speed unit: the knot
