Captains Bold is a free print-and-play game for the age of sail. It focuses on duels between frigates.
Rules: Naval
Iron Ships and Wooden Heads
Iron Ships and Wooden Heads are a set of free wargames rules for naval gaming “in the era of the big gun.”
Privateers War Rules
Ross Macfarlane has a set of rules for privateer raiding actions during the American Revolution.
Men O’ War Napoleonic Sail Rules
Men O’ War is a set of free wargames rules for Napoleonic sail. The rules are aimed at small actions, with one or two ships per player.
Battle: War At Sea Modern Naval Rules
Battle War At Sea is a set of free wargames rules for modern naval warfare. It is designed for 1/6000 scale ships