At the time of Columbus' trip across the Atlantic Ocean in 1492, Portuguese sailors were just beginning to experiment with celestial navigation. Instead of using celestial bodies to fix a ship's position, most navigators relied on dead reckoning. With dead reckoning, the navigator determines a ship's position by carefully tracking the direction and distance traveled from a known point. The ending position for one day becomes the starting position for the next.
For dead reckoning to be effective, the navigator must be able to gauge the course (direction) of travel as well as the ship's speed. During Columbus' time, direction was tracked with a compass, which had been in use since the 12th century. To understand the ship's speed, sailors threw a floating marker over the side of the ship. The ship's railing had two marks, separated by a measured distance. At the moment the floating piece passed the forward mark, the sailor began to chant. The chanting continued until the floater passed the aft (rear) mark. The chant was actually a mnemonic device -- the last syllable chanted signified a measurement of speed in miles per hour. Thus, sailors could estimate the total distance traveled by multiplying the ship's speed by the time of travel.
Speed and distance were measured hourly, and peg boards were used to track the day's journey. At the end of the day, the total distance traveled was transferred to the nautical chart.
Most historians were able to understand Columbus' navigation methods by examining his charts. As would be expected, Columbus's charts show continuous updates of magnetic course and distance traveled along the dead reckoning line.
A short story about Columbus and the Virgin Islands: The Real Treasured Islands
Copyright © 2001-
, Terry Muse