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.
Pete Pellegrino has written a set of free miniature wargames rules called Damn The Torpedos. In the game, you customize your ironclad, and then take it out to fight in the Cvil War battle of Mobile Bay.
The Civil War in 30 Minutes is a matrix game designed by Matt Fritz to help his students understand the American Civil War. If you haven’t looked into matrix games, you will find that they are useful in running meaningful campaigns.
The Battle for Henry Hill is a simulation of the First Battle of Bull Run designed by Matt Fritz for his students. The rules include an order of battle and links to paper figures.