The Reina Christina is an airship that travels between Manila and Acapulco (or Panama City) via Honolulu.
A Spanish vessel, the Reina Christina flies a Hawaiian flag in order to avoid the historical sensitivities of post-revolutionary Mexico (as the captain explains, many Spanish ships are turned away in the port). During refuelling at Honolulu, Passepartout can linger on the beach and bring back the trade good Conch Shell.
Upon arriving on the outskirts of Acapulco, Passepartout may assist the captain by climbing up the rigging and scouting the conditions ahead (an act which will earn him a Brass Telescope). Passepartout turns out to actually be the best man for that job; should he not volunteer, the captain will attempt it himself but fall to his death.
They soon discover the French are laying siege to Acapulco. The captain (or surviving crew) will decide to change their destination further south to Panama City, unless Passepartout had climbed the rigging and convinces them to continue on into Acapulco by stitching together a French flag for the vessel or, should Passepartout have the Rebel Flag in his possession, flying that flag. If you fly the Rebel Flag, the captain will thank you when you arrive at Acapulco, and tell you of the routes to San Pedro/San Francisco and Houston/New Orleans so you don't need to explore and stay in a hotel to get the routes out.