Using the log reel

The log reel was used to measure the speed of the ship.

A piece of wood called a "chip" was thrown overboard. A line was fixed to the chip and a long length of knotted rope was tied to the line.

The knots were tied at 7 fathom (42 feet) intervals and they were timed as they passed over the stern of the ship using a 30 second sandglass.