When fighting Flame Heart the ghost ships cannons will shoot to the center of the island and then towards your ship, this issue makes the cannon balls travel ridiculous distances and also you dont even have to he in the line of fire to be hit.
The escort ships that follow the burning blade seem to be invincible from what I could tell, also, some of the ghost ships take up to 7 shots to be taken down when its supposed to be 3 shots.
