Oh AnthoniusII
You are in for a great treat. We have a whole section of code devoted to naval invasion. The thing is we had to tone it down for this release, and for the typical mod. We can modify the Xcai to perform in whatever way you want with minimal scripting a higher degree of strategic planning. Of course the scripts are great for historical accuracy! The current build will only need tweeked in a few areas to give you what you are looking for. You see it is mostly about path-finding on the map (even water) to have an efficiant xcai. Mikll found that by making the sea all one type and all ships heavy the xcai has a much easier time getting across the oceans.
Our most recent breakthough is pathfinding on the battlefield, you really should try it. It is a great improvement in battle, over the last one and vanilla. We still have issues to deal with, but one by one we are knocking them out. Stone Forts are fabulous and work great on the map. But we still need to figure them out in battles, so they act like a castle for troop deployment.