Vol 1: Spellbound‎ > ‎Read‎ > ‎Ch 12: Lost & Found‎ > ‎

How a Knot is Measured?

Knots measure the speed of a ship. One knot is one nautical mile per hour. A nautical mile is approximately 1.15 miles (6067 feet), based on the distance of one minute of arc on the meridian (a line of longitude from the North Pole to the South Pole). It is called a "knot" because a very long time ago, to measure the speed and distance a ship traveled, a wedge of wood (1.5 feet long) was tied to the end of a rope on a spool. Knots were tied into the rope every 47.3 inches. At the ship's stern the wooden wedge was thrown overboard and the rope was pulled from the spool as the ship sailed forward. Someone would start an hourglass (filled with 30 seconds of sand) while another counted the knots as they passed over the stern board. By doing some quick math, seamen were able to determine how many knots per hour they traveled.