Raise the Black v1.5

From the introduction:

Most adventures in a fantasy RPG take
place on land. It’s so commonplace
that we don’t even think about it. If
boats are ever required (for lakes
or rivers), players expect there to be a ferry they
can hire or some underwater magic path they can
take to quickly cross the waterbody and move on
with their land-locked adventure.

That ignores the 70% (or so) of the surface of the
planet that’s covered in water (give or take how
big you’ve made your land masses on your world).
That’s a lot of territory ignored just because your
adventurers are lilly-livered landlubbers.