Dirty Fred, the Captain (1970)

After getting injured in a fight, the steward of the luxury steamer Honolulu Star encourages Smiling Jimmy to take over the job of the beaten stoker and waiter, in exchange for both of their wages. On the ship, he meets Mr. Irving, who is incognito, playing the role of the Archduke St. Antonio, as he wants to get to know the "underworld" from the inside. They teach each other how to avoid being exposed during their few-day adventure, and eventually, they switch roles. But the real adventure is only just beginning.