© Charles Chandler
Columbus had sailed all over the Atlantic coast of Europe as a merchant captain. Off the coasts of England and Ireland, he had observed that a couple of weeks after a big storm, there would sometimes be tree branches in the water — sometimes from trees not native to Europe. And he knew that the tree branches were not from Greenland or Iceland — they had to be from a more temperate climate. From the wave patterns in the ocean, an experienced sailor can tell how far away the storm was. Putting these facts together, Columbus knew that there was a continent out there, and that it was a lot closer than the estimated distance to China. He was also aware of the Irish and Norse legends of another continent beyond Greenland, visited by Saint Brendan and Leif Erikson respectively.
Columbus also knew about the trade winds, and he was confident that he would have steady winds in both directions, if he traveled at the right time of year and at the right latitudes.
So Columbus' conviction that the round trip could be made wasn't just bad mathematics and dumb luck. It was a conclusion based on facts that others knew, yet Columbus was the one to put it all together. There was another continent out there; it was within sailing distance; and the fastest way to get there and back was to follow the trade winds.
And it is likely that he knew full well that the continent in question could not be the Indies. So why did he not expose his true reasoning?
Columbus was a merchant captain, not a nobleman well-connected at the court of Ferdinand and Isabella. If he had written up an honest business plan and sent it to the monarchs, he would have received a thank-you note and an invitation to stand on the dock to watch as someone more powerful than himself embarked on the journey. And it would have been someone else who would have been made the admiral of the Spanish navy, and governor of all of the new lands found. So it served Columbus' purposes to present a plan based on bad mathematics that no smart person would have stolen.
So why did he never admit that it wasn't the Indies that he had found?
Let's get real here. How was he going to tell Ferdinand and Isabella that he lied to get the funding for the voyage, knowing full well that it wasn't the Indies, but that he still wanted to be the admiral of the Spanish navy, and governor of whatever it was? Admitting to a lie would have invalidated his claim. As long as he could sell the idea that he had found a western route to the Indies, he (and his heirs) had certain titles to it. So he stuck to his original story. And perhaps he didn't mind being thought a fool for having attempted the impossible, and more of a fool for succeeding at it by dumb luck. To encourage further exploration of the Americas, Ferdinand and Isabella rewarded Columbus (and his heirs) for his efforts, and the rest is history.