Monitor’s Screw
It’s funny, and a little scary, how arbitrary the preservation of evidence of our history actually is. As a case in point is Monitor, that remarkable vessel that reportedly encompassed over a hundred new patentable inventions. No official authority bothered to preserve that ship’s construction drawings. They were preserved not by the Navy, which contracted for the ship’s construction, or by Continental Ironworks of New York, which did the actual building, or by John Ericsson himself. Rather, they were saved by Charles W. MacCord, the cantankerous Swede’s chief draftsman. MacCord later served as faculty at the Stevens Institute of Technology, where they would eventually be rediscovered decades later.
Several of these drawings are reproduced in Miller’s U.S.S. Monitor: The Ship that Launched a Modern Navy, including a scale drawing of the ship’s nine-foot, cast-iron propeller, or screw (above). Using this drawing as a guide, I’ve modeled the propeller in three dimensions, after the jump:
And finally, a photo of Monitor’s actual propeller, recovered from the wreck site and now displayed at the Mariner’s Museum at Newport News, Virginia:
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Image: NOAA/Monitor National Marine Sanctuary.
Dead Confederates, A Civil War Era Blog 
Excellent work. An example of a rendering that provides more information than the original article. Blade width reveals slow RPMs. Blade twist evokes sails, perhaps the best available design metaphor of that time. But why iron and not brass? Perhaps the size of Monitor’s screw precluded brass casting or perhaps early nautical propulsion designers missed what their forebears would learn: a busted prop beats a broken drive shaft.
“But why iron and not brass?”
I’m not certain, but I’d speculate it has something to do with convenience and speed, and maybe cost. Monitor (and a couple of other less-successful designs) were built on an emergency basis to be completed before Merrimac/Virginia was finished; the original intent was for Monitor to be able to get in close and destroy the Confderate ship in her own dock. They didn’t quite make it, but they were only 144 days from contract to commissioned, in service. This may be one of those situations where “good enough” had to be good enough.
The Monitor’s revolving turret was the only obvious antecedent of subsequent warships. I hope you get to some more of those other “more than a hundred” innovations. Once you get inside the turret (if you do) the blog at the museum has cool photos of one of the gun cradles being restored.
The number may be hyperbole. But building Monitor did present a variety of technical challenges that has to be addressed on-the-fly, and Ericsson generally dealt with these by coming up with some new gizmo or other to do the job. Most of these were small and relatively unimportant.
The revolving gun turret was an idea that had been kicking around for a couple of decades, and a British naval officer, Cowper Coles, patented one in 1859. Ericsson himself acknowledged the turret had been the idea of many different folks; Monitor‘s happened to be the first one to go into action and prove the concept under fire.