I agree, seafaring types would be rather pragmatic about navigation. You either get them there or you don't. Just the knowledge that the world is round puts you at an advantage. But don't forget that for some of these guys navigation was a secret they did not share openly. Continue that tradition and keep your knowledge to yourself, it increases your power. Knowledge is power, keep it to yourself.

The trick will be to not come off so knowledgeable that you get accused of practicing black magic. The Flat Earth society is alive and well in 1000 AD. Copernicus and Galileo didn't show up until well after 1000 AD and the theory of the Earth not being the center of the Universe hadn't yet received the Vatican's wrath. The church's held to literal scripture even after Columbus discovered the new World.

Whatever you do don't screw up the timeline by writing a book