Yesterday, I dug through my several marine engineering books to learn what I could about the details of the boilers that powered these early steamships. I learned very little that I did not already know. The mechanics of providing combustion air or handling ashes are not mentioned.
So, what can we reasonably infer? The original engines powering most steamships were “low pressure” running on steam pressures of 5-10 psig. For non-technical types, the g in psig means that the pressure is measured using atmospheric pressure (14.7psi) as a baseline. Most of the power generated by these engines, therefore, came from the vacuum caused by condensing the steam leaving the cylinder. Boilers were not designed to generate higher steam pressures and the geometry of these paddle engines did not require it. These power plants were thermally inefficient requiring frequent refueling; one reason for retaining masts and sails. These boilers would not have to be fed with the quantities of combustion air like those generating steam at higher temperatures.
These old wooden warships also did not have the extensive compartmentation of later vessels, so there would be natural ventilation paths within the hull for feeding combustion air to the boilers.
The game changer was the compound, and ultimately the triple expansion engine, but these would not be used until later in the century.
Roger
!
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