I never quite understood the whole compass thing. The unique thing about it seemed to be the fact that it always stayed horizontal (so we're assume that the world already has compasses). How hard is it to keep a compass flat? In fact, it's the first time I've even seen a compass that bothers to stay level.
The market Maou was opening up involved expansion opportunities in the northern, more arid lands.. so it doesnt' even have anything to do with maritime exploration (the only real application I can think of). Even then, can't you float the compass in some water?