In the time frame of CK2, naval battles didn't really exist as naval battles. They were land battles on ships. The idea was to basically attach your ship to their ship so your guys could chop their guys up. Galleys and ramming were the "concept" but in practice, especially after the Roman period (the period we're playing in) there were so few naval engagements and those that did occur were almost always just ships which grappled with each other to provide a bit of "land" for soldiers to fight each other on.