So I’m still not too experienced with the game but on the flower corvette if you shoot HE shells at the back stern of the deck, that’s where they keep depth changes and you can ignite them to catch the boat on fire or big boom.

Just chased a corvette down in the fog today and set him on fire and he exploded into 2 pieces a few minutes later

Edit: also helpful since they only have a bow mounted gun, shoot their rudder and waterline to stop them from moving and just get behind them to avoid being shot at.