Ship captains also used a device called a chip log. Sailors would throw the log overboard with a rope attached. The log was cut and shaped so it would stay in place as the boat moved away. Once the log was in place, sailors let the ship move forward for exactly 28 seconds which they counted using a sand-timer. They tied knots in the rope every 47 feet and used them to measure the distance the ship had traveled by counting the number of knots that went by as the rope played out.

Many words in our language come from the practice of using a knoted rope to measure speed.

	Sailors refer to the nautical mile as a knot because they once measured their speed with knots in a rope.
	Sailors wrote their speed down in a log book.  So-called because it was a record of measurements made with a log.
	Can you think of the name of a part of this website that has its roots in the practice of measuring speed this way?  Click here for the answer.