The term knot, or nautical mile per hour, is used world-wide to denote one's speed through water. Today, we measure knots with electronic devices, but 200 years ago such devices were unknown.
Ingenious mariners devised a speed measuring device both easy to use and reliable, known as the "log line." From this method we get the term "Knot." The log line was a length of twine marked at 47.33-foot intervals by colored knots. At one end a log chip was fastened. It was shaped like the sector of a circle and weighted at the rounded end with lead. When thrown over the stern, it would float pointing upward and would remain relatively stationary. The log line was allowed to run free over the side for 28 seconds and then hauled on board. Knots which had passed over the side were counted. In this way, the ship’s speed was measured.