Five weeks of false starts and frustrating re- tweaking came to an end Tuesday afternoon when the 19th-century iron propeller shaft of the USS Monitor yielded to a piece of 20th-century steel.
Originally scheduled to be separated from the propeller of the historic Civil War ship in mid- April, the stubborn, 9-inch-thick shaft had resisted two earlier attempts by The Mariners' Museum to remove it with a hydraulic ram and a carbide-tipped rotary blade.
But it snapped free with a dramatic pop Tuesday after an hour-long battle with the same guillotine saw - and one of the same sailors - that had teamed up to cut it away from the wreck of the famous vessel nearly two years ago.
"Wrought iron can't be cut with a torch. So you can't use modern methods," said Navy diver Andrew Cowan, who was part of the Little Creek Naval Amphibious Base salvage unit that retrieved the propeller and shaft from the 240-foot-deep seas off Cape Hatteras in July 1998.
"The guillotine saw is slow. But it's a little easier when you're not in the water."
Brought to The Mariners' Museum within days of its recovery, the 4,600-pound propeller and shaft have spent virtually every moment since their arrival immersed in a treatment tank designed to combat the effects of 136 years in salt water.
Though the electrochemical process has removed much of the chloride contamination trapped within the propeller, the 2 1/2-foot section of shaft inside the hub had to removed in order for the historic artifact to be completely treated, said Mariners' conservator Curtiss Peterson.
Dislodging the stronger, wrought-iron shaft from the brittle, cast-iron prop has proved to be an ambitious and risky task from the beginning, however.
Conceived by Swedish-American naval architect John Ericsson, who perfected the invention of the screw propeller years before building his famous Monitor, the 9-foot-tall, four-bladed prop was intentionally designed to be weaker than the shaft, said research historian Jeff Johnston of The Mariners'-based Monitor National Marine Sanctuary.
But Ericsson's ingenious effort to safeguard the Monitor's steam engine if its propeller became fouled also ended up - nearly 140 years later - making it hard for conservators to save the historic prop.
Though cushioned by a thick aluminum plate, its surface began to show signs of weakness when Peterson and his team attempted to pull two metal set keys from the shaft with a hydraulic ram in mid- April.
"Once we saw the aluminum pressing into the cast iron, we said, 'No way!' " Johnston said. "That's how fragile this propeller is."
Historians say the huge artifact is one of only a handful of original Ericsson props known to survive from the 19th century.
It also ranks with the inventor's famous revolving gun turret as one of the most important parts of the Monitor, which made naval history on March 9, 1862, when it met the Confederate warship Virginia off Hampton Roads in the first battle of ironclads.
Though the violent clash ended in a draw, the Monitor sank in heavy seas off Cape Hatteras before the year was out.
And nearly 140 years of exposure to salt water have transformed its momentous iron propeller into something much less robust.
"The surface is no longer metal, but you can still see the original mold marks," Peterson said.
"That's what we're trying to preserve."
Such factors have figured strongly in the museum's shift of plans since its first attempt to separate the propeller from its shaft ended in failure.
Peterson spent nearly a month designing and fitting a complicated lifting rig of plywood cushions, protective plastic covers and steel bearing plates after the museum and its National Marine Sanctuary caretakers decided the shaft had to be cut.
Similar concerns guided Mariners' conservation coordinator Jerry Kinney when the team attempted to slice through the shaft with a carbide-tipped rotary cut-off saw just a week ago.
"It would have done the job. But it would have been labor-intensive - and we couldn't get in close enough to the hub to do it the way we wanted to," Kinney said.
"It also was a hand-held saw, and we didn't want to tear the shaft up."
The guillotine saw used by Navy divers Tuesday, in contrast, was snugged into position a few inches from the hub, then secured to the shaft by a chain.
The persistent back-and-forth motion of its thin steel blade left a kerf less than a quarter-inch wide.
The remaining danger lay in the huge weight of the propeller itself - and in the less than 12 inches of clearance separating its fragile blades and the steel walls of the treatment tank.
So Peterson looked on with apprehension during the last 30 seconds of the cutting operation, when both the propeller and nine feet of heavy iron shaft began to quake.
"That last quarter-inch was pretty hard on me," he said, after the shaft and propeller had parted with a loud snap, then settled back safely into their protective rigging.
"If this hadn't held, I'd be out of job."
VIEWING THE WORK
Conservators at The Mariners' Museum will continue work on the Monitor propeller Wednesday and Thursday, turning the giant, 2,200-pound prop on its side and boring the remaining section of wrought- iron shaft out from inside the hub. Visitors can watch the operation on both days. The museum is at 100 Museum Drive, Newport News, inside Mariners' Museum Park. Hours are 10 a.m.-5 p.m. daily. Admission is $5 adults, $3 students. Call 596-6222 for more information.
Mark St. John Erickson can be reached at 247-4783 or by e-mail at firstname.lastname@example.org