Traversing the Seas
J Thoendell stashed this in Science
On a 16th-century vessel in the middle of the ocean, survival depended on captain and crew knowing their ship inside out, from the nuances of the rigging to how the boat behaved in adverse weather. One thing they didn’t always know was the ship’s exact location. Without landmarks, sailors navigated using a practice called dead reckoning.
To do this, the sailors continually measured two vital parameters—speed and direction. Direction was determined with a compass. For speed, the sailors commonly used the “chip log” method: they threw a line with a wooden float affixed to its end off the ship’s stern. The line was knotted at regular intervals, and sailors timed how many knots came off the spool in a given amount of time (hence the origin of the term knots). Then, starting from their last-known location, the navigator used the speed and direction measurements to plot their current position in the ocean.