I don't want to disagree with the tactics mentioned earlier, but I've been having similar problems to everyone else in capturing ships, until last night. I had a fight with 5 Brit 3rd and 4th rates against a stack of 15 Persiah Dhows. I just sent two lines in, all round shot, no grape or chain, no boarding, and I didn't continue the battle, just ended it as soon as possible, and got 6 captured ships.

Other battles where I've boarded, used predominantly chain to dismast, or continued the battle to the bitter end... nada.