This story was originally published as a web exclusive and updated for the July/August 2016 Top WebEx issue.

Copper spotlighted in restoration of Old Ironsides

Copper consumption worldwide is expected to reach nearly 24 million metric tons this year, according to Statista, a data gathering/market research firm. Copper’s ductility, malleability, thermal and electrical conductivity and its antimicrobial properties make the element attractive, particularly as a sustainable, green building material. 

Twenty-first century architects, contractors and developers aren’t the first to praise the noble metal for its resistance to corrosion and oxidation. In 1758, Great Britain’s Royal Navy used copper sheathing to clad the bottoms of its warships. But it wasn’t to shield the wooden hulls from artillery or the ravages of seawater. The alloy “armor” was designed to ward off the insidious onslaught of the Teredo navalis—commonly called shipworm. This species of mollusk, which proliferated in temperate and tropical waters, posed a greater threat to fleets on lengthy voyages from colder waters. Today the Teredo is found in oceans worldwide and remains notorious for its specialty: boring into and eating away a wooden ship’s hull. 

A 5-ft. section of an original 1795 copper bolt removed from the keel is stamped with the manufacturer’s name, Pary’s Mine Co., Anglesey, Wales.

A warship is born

On March 27, 1794, President George Washington signed the Naval Armament Act, thus creating the United States Navy. Taking a lesson from England’s Royal Navy, its six frigates were copper bottomed. Paul Revere helped to requisition the rolled copper sheathing from England because it was not yet manufactured in America. 

USS Constitution, one of the Navy’s original six warships, was launched from Edmund Hartt’s shipyard in Boston. She earned the nickname “Old Ironsides” when she defeated the Royal Navy’s HMS Guerriere during the War of 1812. USS Constitution maintained a perfect battle record and today is the oldest commissioned warship afloat in the world. 

During her original construction, a lighter weight copper sheathing was applied midship while heavier sheathing was used to cover high-wear sections like the bow and stern. Today, the copper sheets that cover the entire lower hull weigh 6 lbs. each. The high-performance metal has preserved “Old Ironsides” for nearly 219 years.

The new copper sheets, replacing the sheathing done during the 1992-1996 restoration, are 14 in. by 48 in. and have been sourced pre-cut to size.

In May 2015, the venerable frigate entered Dry Dock 1 in the Charlestown Navy Yard for restoration. Work is underway on hull planking and caulking, the overhaul and repair of the rigging, upper masts and yards. Below the ship’s waterline, removal of copper sheathing applied during the 1992-1996 restoration was completed earlier this year. 

“It was a long, laborious process because each copper sheet was held in place with 150 copper nails,” says Margherita Desy, historian for the Naval History & Heritage Command Detachment Boston, which performs the restoration work. “Ship restorers and members of USS Constitution’s crew used crowbars, hammers and pliers to pull the sheathing and the nails away from the hull.”

The next layer—felt—was also removed. The felt had been attached to the ship’s lower hull with bedding compound in 1995, making removal a pretty arduous and nasty job. The ship is 175 ft. long at the waterline and draws 22 ft. of water when floating. “It’s a tremendous amount of square footage to clean, removing the copper sheathing and the felt,” Desy says. “New caulking between the planks below the waterline is also under way.”

When Constitution was built, shipwrights applied lightweight copper sheathing midship and heavier plate on high-wear sections like bow and stern.

Ship shape

The new copper sheets are 14 in. by 48 in. and have been sourced pre-cut to size. The Detachment Boston ship restorers will pre-punch each sheet with an 1852-patented, manually operated punch machine to create the holes for the copper nails. Constitution’s white oak planks are caulked with cotton batting and oakum (hemp impregnated with tar). Traditionally, hull seams would be finished with tar, but restorers today use a rubberized marine sealant. Once new planks are installed and caulked, the hull will be painted and then overlaid with felt prior to installation of the copper sheathing.

“Each copper sheet is attached via the center holes first,” Desy explains. “The edges of the sheets overlap, like fish scales, and are drilled through and then tacked with copper nails.” While the right materials are critical to keep Constitution ship shape, the unique skill sets of the staff performing the work are equally important.

Craftsmanship

When the Navy transitioned to steel hulls in the early 20th century, Desy says, “Much of this artisan know-how for wooden ships was lost. For Constitution’s 1927 restoration, the Navy hired men from the shipyards of Bath, Maine. With a rebirth of interest in preservation and restoration of domestic architecture, wooden yachts and other structures, we’ve been fortunate to find men and women with a wide range of restoration talents. These skills are being taught again and it’s become a competitive marketplace to hire the Detachment Boston ship restorers.”

Ship restorers use crowbars, hammers and pliers to remove Constitution’s 1995 copper sheathing and nails from the hull.

Good, old-fashioned craftsmanship is preserving Constitution for future generations, but it was technology that helped restorers solve a mystery. It began in 1992 when the keel was inspected using radiography non-destructive testing. 

“The keel and the floor timbers—the lowest level of the ship’s frames—are original material and date to 1795,” explains Desy. “Approximately 8 to 12 percent of Constitution is original and it’s all found in the keel and near the keel, well below the waterline. Enormous copper bolts hold this structure together. In the 1992 restoration, select bolts were removed from the keel for examination at the Massachusetts Institute of Technology (MIT) metals laboratory.”

Because the bolts—at 5 ft. long, about half their original 12 ft. length—were 100 percent copper, the laboratory wasn’t able to create a compositional fingerprint. “Since the removal of the bolts in 1992, the Detachment Boston had assumed that all the bolts were made by Paul Revere,” says Desy. “Instead, recent research showed that many of the bolts had actually been ordered from Great Britain and shipped across the Atlantic. When the bolts arrived in America, Constitution’s builders discovered they were too big to fit the holes that had been drilled. So Paul  convinced the builders to let him draw them down to the correct diameter at his North Boston foundry. This manipulation of the bolts became the basis for the legend that Revere had made all of the copper bolts for Constitution. 

Despite its worn appearance, some of the ship’s 1995 copper sheathing will be deeded to the USS Constitution Museum to be turned into souvenirs.

Last October, two English underwater maritime archaeologists contacted the Detachment Boston and the USS Constitution Museum to ask if any of Constitution’s original, 1797 copper sheathing still existed. “We had to disappoint them by telling them we didn’t have any original copper sheathing but we did have these bolts,” says Desy. “Our colleagues asked if we had noticed any stamps on the bolts. We said ‘no’ and then all of us examined the bolt in question and sure enough, they spotted what appeared to be a stamp. Further research revealed that the impressed stamp said ‘Parys Mine Company, Wales.’ This revelation was extraordinary for us and it illustrates that there is still much to learn about this ship.”

The $12 million to $15 million restoration of USS Constitution is expected to be completed in 2017. America’s Ship of State will then be returned to her berth in the Charlestown Navy Yard to welcome visitors interested in learning about America’s naval heritage through this living portal to the past. 

For updates on the restoration, visit www.usscm.org/restoration/blog. FFJ