"Destroy the Man-of-War's masts" is an objective in A Bitter End in Sequence 9
Taking on a Man-of-War is no small feat because of all her guns. Still, fire off broadsides and brace when the shots are coming in. This will help a lot for you to take her down. Using Chain Shot goes a long way to taking the ship down quickly as it removes its ability to move all together.
Now it is time to move in and deal with the crew of the vessel.
