The film is based on two original British steamships, the SS Sirius and the SS Great Western. The SS Sirius was built in 1837 and was serving the London-Cork line until the quest for steam-crossing the Atlantic took her to this adventure. She had condensers which worked with fresh water which allowed less maintenance so quicker journeys. She sailed from Cork and arrived in New York in April 22nd. 1838 after a 18-day trip, only a day ahead of the SS Great Western, which had been specially built for the Atlantic steam crossing but left England (Avonmouth, near Bristol) four days later (so she was faster, but left later). In the film the Sirius, a working replica of which was built, is renamed Dog Star (as Sirius is the dog star), but keeps her original Royal Navy captain's name (Lt. Richard Roberts).
The SS Savannah, an American ship, had been the first one to cross the Atlantic in 1819 from Savannah to Liverpool, only partially using steam power and with no passengers daring to embark considering it too dangerous.