Restoring Old Ironsides - frigate USS Constitution

American Forests, Nov-Dec, 1993 by Eddie Nickens

A wonderful mixture of tomorrow's gadgetry and yesterday's workmanship is helping to refurbish this "floating forest," the most famous fighting ship in American history.

Charlie Deans is playing detective again. He motions for me to follow him into a darkened room, where he turns on a lightbox, wipes from the screen a gauzy layer of wood dust, and places on it a large piece of film. Taking a step back, he examines the image like a doctor analyzing an X-ray.

"Look at that," he says, grinning. "Thanks to four million volts of power, you're looking at wood that's buried 2 1/2 feet deep in the hull of Old Ironsides."

"Old Ironsides" is, of course, the USS Constitution, the most famous fighting ship in American history. Permanently docked at Boston's Charlestown Navy Yard, the ship draws a million visitors each year. As director of the Naval Historical Center Detachment Boston, Deans oversees the maintenance of the legendary 204-foot-long craft. These days, however, he is smiling because he's in charge of a once-in-a-lifetime project, the top-to-bottom refurbishing of Old Ironsides herself.

Every few decades the famous frigate must undergo a "D&I," which in official U.S. Navy parlance stands for "Drydocking & Inspection." Her masts, rigging, and guns removed and hull covered with scaffolds, Constitution has been drydocked since last July, resting on keel blocks and supported by shoring timbers. For nearly two years the ship will be thoroughly inspected. All rigging, copper-hull sheathing, and weak and rotten wood will be replaced and new mast sections made and refitted. The ship will "un-dock" early next year, and the $3.75-million project should be completed by mid-1994.

This D&I is particularly important, for not only is the work more detailed due to the upcoming 1997 bicentennial of her launching, but new technologies have given Deans and company new ways to inspect the ship's complex wood components. Using radiography and sonic and ultrasonic testing methods, workers are now able to peer deep into the ship's 21-inch-thick hull, even through three and four feet of planking and timbers, without boring a single hole or removing a single piece of wood. In addition, new emphasis is being placed on stockpiling the enormous timbers the ship requires for upkeep, an effort aided, ironically, by destruction caused in 1989 by Hurricane Hugo.

All of which gives Deans the chance to play detective.

"See this?" he asks, pointing to the radiograph of a joint in the ship's stem. Light flecks on the film are the remnants of nails, while other checks denote grain patterns. A long cylindrical shape is a metal fastener, one of some 25,000 copper pins--some up to 12 feet long--that hold the ship together. On the radiograph, crevice corrosion on the pin is clearly evident where the two pieces of wood meet, a natural funnel for saltwater intrusion.

Originally, Deans explains, the radiographs were designed to test the condition of the metal pins and fasteners that hold the timbers together. However, the clarity of the radiographs was exceptional, and a careful reading of the film brought added surprises.

"Look closer," Deans says. "Now, this is interesting." He points to a dark shadow on the film. Lighter areas mean the wood is more dense, for it takes longer for the radiation to pass through the fibers, he explains. Darker bands, therefore, denote wood of lesser density. "And if it's less dense," he says, "that means something is wrong; that something is fungus."

Five or 10 years ago, Deans says, the only way to find rotten wood so deep in the hull would have been through destructive methods of testing, such as boring holes and analyzing the cores. But with the radiography, new windows have been opened on wood that hasn't been seen in up to 199 years. All told, some 300 radiographs have been taken of the ship's hull planking and timbers.

In another breakthrough, the U.S. Forest Service's Forest Products Laboratory in Wisconsin used sonic testing to determine rotting characteristics of wood fibers far below the surface. In that process, Deans explains, sensors are placed on both sides of the wood to be tested, an "accelerator" is tapped with a hammer, and the time it takes for the sound to pass through the wood is measured.

Technicians from Wisconsin have come to Boston to test their equipment on the Constitution, and the Navy has sent the laboratory examples of live oak and white oak that exhibited deterioration. Using data from those initial tests as a baseline, Deans explains, they now have some very good ideas about the time it takes sonic waves to pass through various kinds of wood at various stages of deterioration.

"A lot of times," he says, "wood begins to rot from the center--it appears to be perfectly sound on the surface, but the core is rotted. With this method, we went through every one of the beams on this ship and the stem in the stern area, and found several deteriorated that we thought were OK. So we're replacing those."

Wood doesn't have to be ancient to rot, he explains. Perhaps the timbers were installed 20 years ago, but the wood was wet and green. That would be enough to start the destructive process. And unless boring samples had by chance been taken of specific affected areas, Deans says, there would be no way of uncovering the wood rot without this new technology.