The Ghostfaces: The Brotherband Chronicles, Book 6

The Heron band starts out by sailing away to try to avoid a storm. However, they get stuck in a storm that seems to go on and on. There water supply goes low as they are in the middle of the ocean. They decide to gamble on sailing into the unknown ocean in hope of finding land. They barely do in time.
The end up finding a place. They build a fort and set in for the winter. They also defeat a bear and strike up a relationship with the local inhabitants. (There are a few bits of romantic interest.) They also discover there is another from their land with them. His ship was not as lucky. They run into the "ghost faces" and only one survived. Eventually, the winds shift, the battle the ghost faces and head home. They decide not to share the detailed navigation instructions with others to keep the people at peace.
This seems to be a fictionalized version of Viking incursions into America. Here it is explained as people making friends, but specifically not wanting others to go back there. I guess that is as good an explanation as any for an interesting bit of history with little record.