From the Back of the Book:
Fantasy on the High Seas
Might ships cresting waves in the midst of a great storm, Hobgoblin pirates pursuing slow merchantmen, Navigator-Wizards sailing their vessels far beyond the limits of the known world, awesome Battleships, loaded with weaponry, ploughing through the sea with their magically charged rams - these things are as much a part of fantasy as dragons, elves and wizards. Seas of Blood does far more than merely introduce a set of rules covering nautical adventures in the d20 system. It seeks to inject the very essence of fantasy into any gaming session revolving around sea-borne scenarios, taking such games much further than any previous supplements.