In further discussion regarding the Arkansas power plant, I just came across an article by famed correspondent Henry Bentley in the Philadelphia Inquirer dated July 25, 1862 entitled "The Rebel Ram Arkansas: History of the Vessel, Her Construction and Strength." Admittedly a Yankee scribe, Bentley was with Davis' fleet at Vicksburg during the ram's run. I do not know the accuracy of his piece, but quote here several lines for your consideration and opinion.

"Her Machinery: The engines of the Arkansas are low pressure and of about 900 horse power, all placed below the waterline and well protected from injury by hostile missles. Her cylinders are said to be 24 inches diameter and seven foot stroke. She is provided with two propellers, working in the stern and acting independently. These propellers are seven feet in diameter and are capable of making 90 revolutions to the minute. In consequence of the independent action of the engines, one propeller can be revolved forward while the other is reversed, thus permitting the boat to be turned in little more than her own length. A network of iron rods an inch in diameter and with meshes more than a foot across, extends around the upper part of the peopellers to project them from injury by floating logs and driftwood."

I do not know if this makes any sense and leave it to your expertise to offer insight. Thanks. Jack