This is a common scenario with full realism, fire 4 fish at a carrier and three are duds. One hit does some damage;
Not really serious, but it should be easy to catch. Dodge depth charges, creep outside the five mile circle, surface to chase after the CV, do an end around and work in for another attack 6 to 8 hours later;
And somehow the damage control crew managed to do the equivalent of a complete 1 year yard overhaul in 8 hours.

Not much can be done about that, once you let them pirates out of sight they're stacking the deck, marking the cards, slipping aces up their sleeves and loading the dice. No way to fix that, which is why realistic sinking times mods don't work very well.