Well, naval AI can't be compared to what it used to be. Now it has transports, and it lands men. It's dumb at times though; in my last game, Sweden was occupying 2 provinces of a 3PM Danemark; last provinces was a 1 BT island in which there were 5k men. Sweden had 4 cogues. I was a bit mean with AI, so I was funding the danes (1 monthly ducat) to make sure they could afford their army. For more than 15 years, the Swedes sent countless waves of 4k men (they had around 30k standing army...), that got beaten again and again. They were sitting on 75% WS, but not willing to peace out. In the end, they asked for war concessions and no province.