Ramming Speed is a set of free wargames rules for righting naval battles with ancient galleys. The rules are designed for 15mm models.
galley
Fleet of Battle Ancient Galleys Wargames Rules
Fleet of Battle is a set of free wargames rules for playing out battles between fleets of ancient galleys. Think Ben Hur. There also are several pages of free print-and-play galleys for use in lieu of lead miniatures. The rules require a knowledge of the commercial Field of Battle wargames rules.
Capitana Wargames Rules For Galley Warfare In The Mediterranean
Ray Lucas offers Capitana, a set of naval rules specifically for 16th Century galley warfare in the Mediterranean. They were written for the NLWG 2009 convention game.
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:
15mm War Galleys
Here are a set of instructions for building 15mm models of ancient War Galleys from the Jackson Gamers.