How are we supposed to get the obsidian bone crusher set?

In order to unlock it you need to sink the burning Blade crewed by players 10 times. But it's basically impossible. Today me and my 2 friends (all about 200 hg levels) attacked a galleon burning Blade with a swabbie crew. They were ass in pvp and we constantly pressured with about 300 cannonballs but they turteled and all 4 bailed and hardly shot cannons. Eventually we ran out of cannonballs and had to retreat with the chest of fortune. Experienced crews can absolutely obliterate anyone who cares to get close to them because they don't have to bother about repairs. Does it have any weaknesses?