The trick is that you are ships engineer needs to be set to reload torpedoes you need to have about 15 to 20 high-end torpedoes (bft or voron) and now the most important point: when there's only one ship left in the first encounter you need to play around with it a bit to give your engineer a time to reload all your torpedoes for the next round. Best way to play around with that ship is just to play hide and seek, and shut down any missile it might launch you .
sorry for the crappy writing, but this is voice recognition cause I'm using my mobile phone now.