Captains Bold is a free print-and-play game for the age of sail. It focuses on duels between frigates.
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.
The Immortal Memory
The Immortal Memory is a set of rule for refighting Trafalgar.
Shot and Sail Napoleonic Naval Rules
The prolific Jim Wallman offers a set of free wargames rules for Napoleonic Warfare called Shot and Sail. In addition to the pdf fo the rules, you’ll need the zipped graphics of ship cards.
Nelsons Wars: Napoleonic Naval Rules
Andy Watkins offers Nelson’s Wars, a set of rules for miniatures battles in the age of fighting sail. The mechanics are based on the Silent Death rules, which use dice of different sizes (d4, d6, d8, d10 etc.) to distinguish between different weapons systems.