Empires of the Seas is a set of rules for the Age of Fighting Sail. The author says that the rules allow battles between large fleets without lots of record keeping.
Rules: Naval
Firepower Naval Rules
Firepower is a set of free wargames rules for naval battles. The rules cover the period 1900 – 1945.
A Hotter Fire ACW Naval Rules
A Hotter Fire is a set of free wargames rules for naval combat between civil war ironclads.
Away With Honour – Middle Ages Naval Warfare
Away with Honour is a set of free wargames rules for naval warfare in the Middle Ages by Tony Cullen.
Der Tag Naval Rules
Der Tag is a set of free wargames rules for WWI naval warfare in 1/6000 scale.