The only way in game, as in reality to reduce hull damage is...
... to spend two months in base for repairs in dry dock.
sorry, There is just no way around it. Minor repairs like damaged pumps, torpedo tubes, radios etc can be repaired at sea generally speaking... but serious hull damage (ie you took a bomb hit or a shell hit or a major depth charging) can only be repaired in reality by removing the boat from the water in a dry dock and getting a fully equipped work detail on the job, this is a time consuming process involving workers, engineers, maritime architects sometimes, all of whom have to be familiar with the ship, and capable of restoring it to seaworthy condition by reference to schematics, blue prints etc. The game simulates this by sticking you in port for a long enough time to simulate those repairs.
If i understand your question right, there isnt really a way to fix hull damage at sea using a damage control team or any sort of trickery or slight of gaming hand so to speak