The Pirate Ship is a boat that travels from Muscat to Karachi. This route is opened up by conversation choices while exploring Muscat.
Passepartout can be robbed on this journey, though the chance of this can be mitigated if Passepartout is armed, even if only with an improvized weapon such as a Monkey Wrench. With the right conversation choices he can obtain the trade goods Cutlass and Ball-bearing.