The Pirate Ghostship is one of the vehicles used in voyages. It doesn't need building but can be upgraded. Voyages take 50 actions to complete and crew members are added for a period of 28 hours. The voyages unlocked with the pirate ghostship are: Ghostbeard's Boo-ty (2 crew members), Witches of Brunswick (4 crew members) and Vlad the Vampire (6 crew members).
Upgrading the ship costs 75 cash and adds 3 permanent crew members.