Special Report: Conservation

A blast from the past

By Lynn Stanley

Above: Scientists perform the tedious job of removing marine concretion from the exterior.

Meet the iron submarine that changed the course of naval warfare

September 2017 - Market pressures are squeezing fabricators to manufacture parts better, faster and cheaper. But what if we could press pause on production for a moment, step away from the stresses of modern metalforming, and take an educational mini-vacation to the Warren Lasch Conservation Center (WLCC) at the Clemson University Restoration Institute in North Charleston, South Carolina?

There, senior archaeologist Michael Scafuri and a staff of conservators and archaeologists are painstakingly unraveling a 150-year-old maritime mystery. The plot? It was the height of the American Civil War. The place was Charleston, South Carolina. Metalworkers—blockaded from supplies by Union ships—crafted a combat submarine from cast and wrought iron for an audacious mission that changed the course of naval warfare.

H.L. Hunley penned its opening chapter on Feb. 17, 1864, when it became the world’s first attack submersible to sink a ship. The Confederate submarine, armed with a 16-ft.-long spar torpedo [a long spear with an explosive charge] loaded with approximately 135 lbs. of gunpowder, sank the steam screw sloop-of-war USS Housatonic. After unleashing its lethal blow, Hunley and its eight-man crew disappeared beneath the waters without a trace.

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H.L. Hunley was transported by barge to the Warren Lasch Conservation Center at the Clemson University Restoration Institute.

What happened to the vessel and its submariners remained an enigma until 1995 when American adventure novelist and underwater explorer Clive Cussler and his National Underwater and Marine Agency (NUMA) located the missing vessel using remote-sensing equipment, side-scan sonar and a magnetometer. Submerged in approximately 30 ft. of ocean and entombed in sediment nearly 5 ft. thick in places, Hunley had never left the harbor.

Raising Hunley

In 2000, after five years of meticulous planning, Hunley was raised and transported to WLCC, where it was immersed in a fresh water conservation tank. In 2001, the remains of the crew were recovered.

In 2014, scientists began the tedious, delicate job of removing nearly 11 tons of concretion —a mixture of shells, sand and corrosion byproduct—from the submarine’s surface. They used small pneumatic chisels and dental tools. To further loosen its outer crust, Hunley’s bath was changed to a solution of water and sodium hydroxide. In September 2015, after 12 months of exacting manual labor, nearly 70 percent of Hunley’s exterior was visible for the first time.

Holes, scratches, damage and other items offered a roadmap of clues to as-yet unwritten chapters of Hunley’s story. Its iron skin also told a story about workers who grappled with time and intense pressures to create what underwater archaeologist Harry Pecorelli III called “a work of art.”

At its core, archaeology is the study of the physical evidence of the past, says Scafuri, who also serves as adjunct professor of historic preservation at Clemson. “Through investigation we are looking to interpret events, to determine what the remains tell us.”

Partnering with the Naval Surface Warfare Center, Carderock Division, to model, simulate and test the underwater explosion of Hunley’s torpedo, Scafuri may be able to determine its effects on both the ship and the submarine.

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Scientists use pneumatic chisels and dental tools to remove concretion.

“We are attempting to understand a significant event in naval history,” he says. “We want to know how and why eight men cranked an experimental craft four miles offshore to sink a ship. How did this event affect the war, if at all? And how did this event fit into the changes taking place to naval tactics and design at that time? This is the story we want to tell.”

Vintage ironwork

Scafuri says he is also interested in the submarine’s design and the goals of its builders. “Historical records are spotty but we know these metalworkers were under pressure with few resources. It seems logical they would just throw something together. Instead, they built a streamlined, elegant vessel that could cut through the water with its knifelike shape.”

Since the late 1700s, rolling and slitting mills were capable of forming and cutting flat iron sheets or rails. Through the mid-1800s, blast furnaces remained an effective method for producing iron for casting. But the process of transforming cast iron into wrought iron remained woefully inefficient in the United States. According to historian David Landes, the puddling furnace “remained the bottleneck of the industry,” requiring men with a constitution strong enough to withstand extreme heat while stirring molten metal to catch and draw off globules of wrought iron that formed on the surface.

On Dec. 20, 1860, South Carolina became the first state to declare secession from the United States. The same year Tredegar Iron Works in Richmond, Virginia, became the third largest iron smelting operation in the U.S. and was a key reason the capital of the confederacy was relocated from Montgomery, Alabama, to Richmond.

Tredegar Works served as the primary iron and artillery production facility of the Confederacy. Hostilities began April 12, 1861, when rebel forces attacked Fort Sumter in South Carolina. In late 1861, the U.S. Navy blockaded ports like Charleston to prevent access to trade and goods needed by the Confederacy. The South also began to armor wooden ships with iron plate, a practice quickly followed by the North.

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The detached rudder of Hunley before [left] and after [right] conservation treatment.

CSS Manassas was the first ironclad to enter battle in 1861 a year before USS Monitor arrived.

The cast and wrought iron Hunley measures 40 ft. long from the forward end of the bow casting to the aftermost point on the stern; 4 ft. high and 3.5 ft. wide amidships. “That’s 12,000 lbs. of iron that could have been used to build cannons,” Scafuri surmises.

A series of 3⁄8-in.-thick wrought iron plates were used to make the hull. Plate edges were carefully fitted up against each other and riveted to iron backing straps on the inside. Iron stiffening rings were installed to support hull pressure at depth. Scafuri estimates there are 42 plates.

Riveting story

Between the 1840s and 1940s, rivets were the primary fastener used in shipbuilding. The conventional hot riveting technique typically required three to four people; one to heat the rivets and then pass them to the “catcher,” who inserted the rivet into the hole; a third fellow who hammered the rivet into the hole and the fourth, who held the rivet in place with a dolly.

“On Hunley, iron plate edges were beveled and the rivet heads hammered flush with the surface,” says Scafuri. “This method allowed them to achieve a smooth outer surface and minimize drag. There were roughly 100 rivets per plate. The craftsmanship was superior. In order to remove plates to gain access to the interior, we had to drill through the rivets. We went through a lot of drill bits trying to drill through those rivets.”

The bow was sculpted to a thickness of 1 in. A tapered keel was ballasted with iron blocks contoured to match the hull. Metalworkers achieved tapered ends by fashioning four narrowing rows of up to four wrought-iron quarter plates each. Quarter plates in these sections totaled 28.

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The hull interior was supported by half-moon shaped iron rings, joined with bolts and a slotted plate, tightened with wedges.

In an era before power tools—gas welding and cutting, followed by arc welding and resistance welding, wasn’t developed until the late 1800s—Hunley shipbuilders instead cast complex components like the submarine’s end caps and riveted them to plates. The availability of materials may have limited the submarine’s size, but they also knew that the larger they built the submarine, the more slowly it would move, says Scafuri. Despite cramped quarters, seven of the crew turned an iron crankshaft attached to a propeller with three wrought iron blades riveted to a cast iron hub. “It’s a smart design,” Scafuri notes. “If any of the blades were damaged, they could be replaced without replacing the entire propeller.” Addition of expansion strakes to the sides of the submarine’s hull increased its interior headroom.

“With standard shipbuilding, mid-ship is your center point,” explains Scafuri. “The keel, stem and stern post give you a skeleton. The submarine doesn’t have a keel so we’re using reverse engineering to try to determine how they laid it out. We hope to gain some insight into what they were thinking and why they did things the way they did.”


Dive planes and remnants of other submarine components, including ballast tanks, are “evidence of the innovation and care of the submarine’s designers and builders. We know they designed Hunley to dive because the depth gauge capped out at around 30 ft., which tells us how deep they intended to go,” says Scafuri.

“The spar torpedo was produced in three pieces. A 3-ft.-long cast iron rod attached to the tang [a projection] at the forward end with a yoke was inserted into a rolled, wrought iron pipe 6.5 ft. long. It was joined with a second wrought iron piece 6.5 ft. long. The tip of the spar contained a fragment of the copper sheathing used to encase the torpedo, which was bolted to the spar.

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An automated system drains Hunley’s treatment tank, allowing scientists to perform tasks such as the deconcretion visible on the port side.

Finding the torpedo’s remains at the end of the spar support the idea that it was not meant to come off the spar. For Scafuri and the others, a lot of research and analysis remains to be accomplished. But clues like the discovery of the spar and its pieces, the hull and the mechanisms the crew used that night unveil “previously hidden details” that Scafuri believes will prove essential to the group’s investigation to understand what really happened to Hunley and its crew.

Were the submariners knocked unconscious by the shockwave of the explosion? Was the ship structurally damaged? Since the crew died at their stations, did the vessel simply run out of air? Deconcretion and restoration work on the submarine will take three to four more years to complete.

“Archaeology is the study of people and the lives they lived. How valuable this is to the present is subjective,” Scafuri says. “But I do feel that making a connection with the past helps individuals put the present into perspective. It can be illuminating to learn about the lives of people 150 years ago, how they solved problems and how similar they are to us.”

Perhaps fabricators today can find a similar kinship with metalformers like those who crafted Hunley with imagination and grit. FFJ


  • Friends of the Hunley
    North Charleston, South Carolina
    phone: 843/743-4865

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