Thanks for the advice. I wonder if revisiting Navy Gray (Maxine Turner) might be useful. Because of her boiler explosion, there may be rosters of crew somewhere on the net. Perhaps knowing the number of engines and boilers from that vessel, I can figure out something reasonable for the other. From the scant description available, it appears two horizontal direct-acting high-pressure engines with a short stroke, each driving a single shaft and propeller. The air management issue is interesting because there was no blower for forced air - all from draught. I've been doing some research into the high-pressure engines the British were putting into the Crimean gunboats. They were the first mass-produced units and didn't run a condenser. At the higher speeds to drive props they needed a lot of maintenance. The British had to outfit a floating support vessel for Hong Kong in the mid-late 1860's to support a squadron there. I'm interested in this because the Confederates appear to have gone two routes for propulsion before their engine shops at Richmond and Columbus got their act together. They tried adapting high-pressure riverboat engines and apparently had to go to a gearing system to gear up to the rotational speeds needed for screw propulsion. I think there is also evidence that they tried to build high-pressure, high-speed engines, direct-acting. Seems to me that the short-stroke and drive-lines gave them trouble. The British of the period were going to multi-plate, oil filled thrust blocks on their drive-lines. They also used dog-clutches in case of an engine shut-down or to decouple the prop(s) if the vessel was going to her sailing rig and didn't have a lifting screw. I suspect that the Confederates didn't do any of these things on home-built vessels. I also have reason to believe some of these installations had resonate frequency problems in the drive-lines that exceeded the specs on the wrist pins. Makes you wonder about how critical the alignment was on the drive-shafts. The tolerances had to be pretty loose. I also wonder about bearings on the higher speed engines.