Navigation Methods of Medieval Times as Used by Christopher Columbus
Tuesday, 11 September, 1492. Steered their course west and sailed above twenty leagues; saw a large fragment of the mast of a vessel, apparently of a hundred and twenty tons, but could not pick it up. In the night sailed about twenty leagues, and reckoned only sixteen, for the cause above stated.
Friday, 14 September, 1492. Steered this day and night west twenty leagues; reckoned somewhat less. The crew of the Nina stated that they had seen a grajao, and a tropic bird, or water-wagtail, which birds never go farther than twenty-five leagues from the land.
These are excerpts from the logbooks of Christopher Columbus, the adventurer who revealed a ‘New World’ to Europe. Columbus was a keen navigator during his time. So obsessed with his skills was he that he was certain he had landed on the fringes of present day China during his first voyage! Little did he know that he had touched the edge of the two continents that stood between Europe and the East.
Columbus was the first sailor to keep a detailed log of his voyages. These logs have helped historians understand the different methods of navigation used in medieval times. The sailors in those times used two kinds of navigation methods. One called Celestial Navigation and the other called Deduced Reckoning Navigation or Dead Reckoning Navigation (DR Navigation).
Columbus’ logs do not mention celestial bodies. A celestial navigator observes celestial bodies to determine latitude. Each star had celestial latitude. If you knew this of the star directly above you, you were at exactly the same latitude on earth. Instead ‘Reckoned is a word we often come across in his logbooks. Evidence from researches has pointed to the fact that he was primarily a DR navigator. Hailing from Genoa in Portugal, he learned to use this technique from Genoese pilots. Dead reckoning is simple arithmetic. The navigator measures his course and distance from a known point say a port, by pricking a point on a chart and then measuring the distance. This new point would then be the starting point for his next day’s measurement.
How did they measure the course and distance sailed? The course was measured by the compass and distance was calculated using time and speed. Simple arithmetic?
Here’s how
Dead reckoning is moving a set distance along a set line. Imagine you are traveling by car. If your car is moving at a speed of 20 miles an hour for 3 hours, the distance you have covered in this time is 60 miles in the direction you have chosen, which is 20 times 3. If you wish to find out your cars position after a certain number of hours you will need to record the speed, time and the direction including any changes in these during the journey.
How did they measure the speed in water? This required that the navigators measure the course and the distance covered. In order to measure this the sailors made two marks on the rail of the ship. A float was then thrown overboard and allowed to trail. When it passed the forward mark, the pilot would start a quick chant. This chant was an old medieval chant used in navigation. He would stop when the float reached the rear mark. At this point, the last syllable of the chant was noted and he would convert it into a speed in miles per hour using a mnemonic. However, this method did not work when the ship was moving very slowly because the chant would be over before the float reached the rear mark!
Some researches suggest that Columbus judged the ship’s speed through his own version of dead reckoning. Knowing the time elapsed between changes in his vessel’s speed and direction of travel, Columbus entered his estimate of distances in a log. Columbus may have measured speed used a rope one end of which was tied to a wooden float. The rope was knotted at regular intervals. The end with the float was then thrown overboard and the rest of it piled on the deck. As soon as the float touched the water, an hourglass was turned so that the sand began dropping to the bottom portion of the hourglass. The rope was allowed to trail until the sand in the hourglass emptied into the bottom portion. The length of the rope that was pulled into the ocean when the hourglass emptied completely gave the distance and of course the hourglass gave the time. Columbus could also determine the speed of the ship from his feel of the keel moving through the water. So keen a navigator was he!
In this manner, speed and distance were measured every hour. The direction the ship moved was measured using a
compass. The officer of the watch noted these down using a kind of pegboard called toleta. The board had holes radiating outward from the center along every point of the compass. A peg was moved from the centre along the course and distance traveled for that hour. After a few hours another peg was used to mark the course and distance covered. At the end of the day, the pegs would indicate the distance covered during the entire watch. The total distance and course was then transferred to a chart. This is how Columbus’ navigation was maintained in logs that we see today.
