What were the two errors Columbus made on his sail?

Answer 1

Christopher Colombo of Genoa had always dreamed of finding a shorter route to China since he was a young lad enamored of the stories of Marco Polo's travels. In his apprenticeship sailing in the Meditteranean and the Atlantic he had heard stories circulating among sailors of large land masses but 900 leagues (2700 miles) to the west of the Atantic coast of Normandy and Brittany. He believed that it had to be China or at the very least the more mysterious Japan. The stories were indeed true, for the fisherman of these two areas of present day France had been landing on the shores of Newfoundland and Nova Scotia, chasing the great schools of cod on Georges Bank. Archeological evidence discovered in the last 30 years by the Canadians has found traces of camps set up on coast of North America by Breton fisherman from the late 1300's on to facilitate the drying and perserving of their catch.

Armed with this information and crude maps drawn from these tales Colombo tried for 10 years to persuade Iberian rulers to outfit and finace an expedition. The Portugese laughed him out of the court because they already knew that his geography was wrong. The court of Portugaul, since the time of Henry the Navigator, knew that the circumference of the world was some 24,000 miles. They knew this because the Greeks from the second century BC had known it by the application of trigonometry using sun angles observed some distances apart. The Portuguese knew that Colombo was in error before he ever did, which was mistake number one.

Colombo's second mistake was common to all navigators of that time in that while one could reasonably judge how far north or south you were using sun angles on an Astrolabe, charting your position east or west was at best a guess until the invention of the chronometer (a really good watch that does not lose but a minute over several months) in the late 1700's. So while his desire to reach China caused Colombo to underestimate the distance to Asia his faulty longitudal navigation cause him to overestimate his travels.

So simply stated his two problems were one of Geography, which is unforgivable for scholars and royal navigators already had the correct information and secondly of navigation, of which all explorers suffered until the dawn of the 19th century.

Answer 2

1) He greatly underestimated the size of the Earth

2) He had no idea that two continents lay in his path

Answer 3

He significantly underestimated the diameter of the Earth leading him to believe the western distance from Europe to Asia was thousands of miles less than it actually is.