Red Fleet at Dawn is a set of free wargames rules for Cold War naval battles.
Rules: Naval
Coastal Command WWII Naval Rules
Coastal Command is a set of free wargames rules for small coastal craft in World War II.
Nauta Ancient Naval Wargame Rules
Nauta is a set of free miniature wargames rules for playing out ancient naval battles. The files are hosted here:
Age of Sail House Rules For Savage Worlds
Tim’s Miniatures Blog has some Age of Sail House Rules for Savage Worlds. He also has some Savage criticism of those who wrote the Pirates of the Savage Main rules.
Smoke On The Water Civil War Iron Clads Rules
I have a large collection of 1/1200 Civil War Ironclads but have never played many games with them becuase I haven’t really found a set of rules I liked. I may give theis free set called Smoke on the Water a try.