Could steam generators, rather than conventional boilers, have served as a ship's main propulsion system?
Short answerPotentially, but by the time the approach was efficient enough, better competing systems were available.
NotesThe proposed steam-generator approach could potentially serve a ship's main propulsion. The objection is timing rather than simple impossibility. By the point at which the system became efficient enough, other propulsion options were already better. A workable technology can still miss its procurement window when competitors mature sooner.