Hey verkle

Perhaps these questions remain unanswered for you because you failed to look, preferring to assume and imply some supernatural guidance for early explorers.
http://en.wikiped...vigation

-These people had many practical ways of navigating across the ocean.

Really, you need more than one book to understand the world.

mimic conditions from the 800s to the 1600


approx. the Viking warm period

The REAL answer is even simpler than that!
They just used their "Frequent Sailing Miles"!