The Book of the Sea (2004)

From the Back of the Book:

Featuring new spells, tactics and prestige classes, and whether in pursuit of profit or prey, The Book of the Sea presents all the information necessary to sail the infinite seas.

From selecting a ship, it's crew and fittings to the journey itself, every aspect of adventuring, both above and below the waves, is detailed here, expanding not only nautical travel, but those ports, monsters, and even those random occurrences that plague those who would wander the seas of the world. Including rules for mutiny and the punishment of those who would dare to test their captain's authority, as well as a Ship's Log system to measure the weeks or months at sea that can try the will of the toughest sailor.