Slowly & Carefully The H.L. Hunley Is Set Upright
By Scott C. Boyd
(August 2011 Civil War News)
Workers on the port side of the Hunley check their chain falls for the next incremental shift of the Confederate submarine in its journey from a 45-degree list to starboard to being upright.
(Friends of the Hunley/Cramer Gallimore photo)
CHARLESTON, S.C. – “It looks so much more menacing,” was marine archaeologist Benjamin Rennison’s impression of Confederate submarine H.L. Hunley’s new look after it was rotated in June.
Rennison participated in the ship’s rotation, which took place from June 22 to June 27. It took a total of 23 people working from roughly 8 to 5 each day for four days. They had to get it right the first time, because there is only one Hunley.
The Hunley had not been upright since it sank following its successful attack on the USS Housatonic on Feb. 17, 1864. The Hunley was the first submarine to sink an enemy ship in combat, but it was not seen again until its discovery in 1995 just outside the mouth of Charleston Harbor.
The Hunley has been at the Warren Lasch Conservation Center since its recovery from the sea on Aug. 8, 2000.
The Hunley was discovered at a 45-degree list to starboard in 1995 and was kept at that angle during and after it was recovered, and has been housed the same way in the conservation center.
As a former Confederate warship, the U.S. Government holds title to the Hunley, and by programmatic agreement, the State of South Carolina has perpetual custody of it. Clemson University operates the conservation facility.
Rennison, a Clemson employee, said that intense planning for the rotation was under way for 18 months (see September 2010 CWN).
Any engineering plans for the Hunley, such as the one for rotation, must be peer-reviewed and approved by five levels of management, he explained.
First, plans were sent to the Clemson conservation department; second, to the Clemson engineering department; third, to an outside engineering group; fourth, to the state’s Hunley Commission; and, finally, to the U.S. Navy.
One of the biggest challenges the Hunley team faced was that such a rotation had never been done before. “With this project, we’ve had to ‘write the book’ because there’s only one Hunley,” Rennison said.
He is a 3-D scanning specialist. Through photogrammetry, the science of making measurements from photos, Rennison helped assess whether the sub’s hull became deformed during the turning process.
Before the rotation, Dr. Vincent Blouin, assistant professor of materials science and engineering, created a finite element analysis model of the sub.
Some of his data came from Rennison’s 3-D laser scans of the hull surface.
“He assessed every single rivet, every rivet hole and every plate on the sub and created a computerized model of the stresses that would happen with the rotation,” Rennison said.
Blouin simulated many different rotation techniques with his digital model to discover which one would work best.
Rennison built a two-meter-long full-scale mockup of a portion of the Hunley’s hull to further explore the effects of a rotation on the shape of the sub’s hull.
He also helped build a training device to teach people how to execute the rotation.
When it came time for the actual rotation, each of the 15 slings holding the Hunley had load cells attached to carefully monitor stresses on the hull.
Rennison attached a laser to the sub’s stern and a laser dot on the bow.
“If it strayed a couple of millimeters from that center point, that meant we were having a detrimental occurrence,” he said.
As it turned out, “We didn’t really have any significant change – that told us our calculations were good.”
The sub in its sling cradle was shifted about 0.33 degrees per movement, according to Rennison, for a total of about 135 movements.
There was one person on the port side for each of the 15 slings holding the sub. There were three on starboard. Two people took continuous angle measurements. One person on computer monitored the load cells on each strap. The head engineer oversaw the work. A caller ordered each movement.
Chain falls, with a pull and release mechanism, were operated by the 15 people at the slings.
At the time, the people helping did not think the sub moved because the movements were so slight. Rennison said that only after reviewing time-lapse photography of the work could they see that the hull was slowly being rotated. They paused a couple of minutes between movements, he said.
While they worked with the Hunley out of its fresh water tank, where it is kept to prevent corrosion, a sprayer system kept it wet.
An area on the lower starboard side of the sub was visible for the first time after the rotation.
One thing exposed was the ballast blocks on the Hunley’s keel. These kept the sub upright in the water. They had release screws the crew could use to detach them to give the vessel extra buoyancy in an emergency.
“Some people thought the ballast blocks were of a different design, but they just turned out to be heavily concreted,” Rennison said.
There is still considerable concretion to deal with. Rennison said that 95 percent of the Hunley’s hull is covered with it, inside and outside.
The conservation team has to be careful about removing the hard sediment, he said, because it has been like a Band-aid protecting the hull from corrosion.
Inside the sub, the concretion has the consistency of toothpaste, according to Rennison.
However, you can’t just scoop it out, because it is so closely bound to the hull surface. If it were picked it off by hand, some of the hull would come off with it.
Rennison reported thinning of the hull on the starboard side. This was the part sticking out of the sand while underwater. Over time, the sea currents washed over the exposed side, scouring it. “It’s like a belt sander went over the hull,” he said.
The large hole forward and the large hole aft on the starboard side were the result of corrosion, Rennison said, not battle damage.
The narrow bow and stern sections are made of cast iron, whereas the middle of the hull is wrought iron. The different kinds of metal joined together caused accelerated corrosion, leading to the thinning, he explained.
Since the rotation, the Hunley looks like a new sub altogether.
“Before it looked like a wounded warrior. It was just laying on its side and immobile,” said Rennison.
“Now that it’s upright, it looks so much more menacing. There’s an appreciable change in its potential. You look at it, and it looks like it’s ready to go.”
For more information, visit www.hunley.org.