The ghost ship in Skull and Bones is called the Maangodin. It is a spectral vessel that haunts the open seas and is one of the most challenging enemies you can face in the game.
The Maangodin is only vulnerable to attacks on its weak points, which are two glowing skulls located on the front and back of the ship. Once these weak points are destroyed, the rest of the ship becomes vulnerable to your cannons.
Here are some additional details about the Maangodin:
Defeating the Maangodin will reward you with some of the best loot in the game, including the Blue Specter weapon, a powerful cannon that fires spectral projectiles.