Comment: There was plenty of evidence for a round Earth at the time,

(See in situ)

In reply to comment: The most historic example (see in situ)

There was plenty of evidence for a round Earth at the time,

and despite modern myth, the going consensus at the time was that the Earth was indeed round.

http://www.todayifoundout.com/index.php/2013/05/people-in-co...

Columbus did not sail West on a guess or a hunch.

The question wasn't of the roundness of the Earth, but how much empty ocean you had to sail through to reach land, and thus, if it were possible to make the journey with the supply limitation of modern ships.