Corvus is a set of free wargames rules for fighting ancient sea battles.
David Heading offers a set of Renaissance Naval Rules.
Togo is a set of free wargames rules for naval battles during the 1904 – 1905 Russo-Japanese war.
Schnell Rules is a set of fast play rules for WW2 coastal forces.
Mike Callan offers this set of free wargames rules for American Civil War Ironclads. The set originally was published in Wargames Illustrated 14.