Given that battles take a while already I personally find that the ability to repair a ship during battle makes it unbalanced.
I agree that sail repair during battle is a good thing, but having to fight a near new ship at times when you've almost sunk them is a pain.
I have loaded up on all the repair perks once and still didn't seem to get the same amount of repair as other players that I have fought against.
Last PvP I did I had the player down to a slither of armour both right side and rear, they popped a repair and increased those areas by a good 25 to 30% which is greater than the 10 to 15% I ever seem to get.
Not sure if anyone else thinks this way, but I would like to see the ability to Ship repair decreased or taken out completely from the game. Rebuilding the side of a ship mid battle seems a little odd, but that's only my opinion on this matter.