Not so. In a naphtha launch, the naphtha takes the place of what would be water in a closed-system steam engine. A boiler turns the naphtha into steam (it has a very low boiling point) and sends it to a little compression (steam) engine. The exhaust circulates back through a condenser, where it turns back into liquid and recommences the cycle. Can you imagine boiling gasoline and running it through a steam engine?
If you read enough old newspapers or yachting magazines, you will find stories about explosions of naphtha launches. They really lived dangerously in those days.
New York City