First get the biggest ship as you can afford. Then buy 500 heavy cannon balls. Then find a town with less then or equal to two defence cannons. This is easy when using two of the "In The Line" ships with full cannons to ensure a victory. The accuracy bonus also helps. If you get challenged to a dual, mainly use defence then go for these following moves. Left shoulder, Left knee, Right shoulder, head, stoumgh, right knee, then defence until you reach full blue in the bar and repeat until the captain surrenders.