Ghost ships in many stories refer to those mysterious vessels that disappear and then reappear empty and deserted.
But for a Necromancer, the so-called ghost ship is literally what it means—a ship's spirit.
As a means of transportation, a ship is unlike any other because on the high seas, you can only trust the vessel beneath your feet carrying you, and the sailors' emotional investment in their ships makes them different from other vehicles.
In the age of sail, every ship bore the sailors' courage and faith; they believed that the ships they were aboard were part of their crew, companions who shared their fate and fortune.
After all, on the boundless ocean, one can only trust the ship beneath them because it is the ship that allows them to survive and chase after riches or dreams.
In such circumstances, every ship naturally became a vessel for the sailors' trust in the ship itself, and this trust naturally equated to the power of faith.