I've noticed that AI fleets don't get repaired at least when they are in a trade theatre. Now the only way to repair right now is to bring them into port wich the AI is usually far from.
I've captured 3 2nd rate ships from the AI due to this not because my ships were superior but the second rates were so battered from AI vs AI autoresolve (probably pirates) that they usually had no more than 30 cannons left and a very weak hull
I'm thinking the game needs to allow repairs at sea for the AI's sake
Maybe taking up to 5 turns or more to be repaired but while in port they only take 1
The human player is smart enough to take a battered fleet back to port whereas the AI just sits there with sitting ducks paying high upkeep for a ship that can easily be captured