Conservation-restoration of the H.L. Hunley facts for kids
The conservation-restoration of the H.L. Hunley is a big project happening right now. Experts at the Warren Lasch Conservation Center are working to save this famous submarine. The Hunley was found in 1995 and brought up from the ocean in 2000. Since then, a team of conservators has been working hard to restore it.
The Hunley is special because it was the first combat submarine to successfully sink an enemy ship. It has been at the Lasch Conservation Center for over 15 years. Scientists and conservators are carefully planning its restoration. Once the work is finished, the Hunley will move to a new museum built just for it in North Charleston. Right now, visitors can tour the conservation center and see the Hunley in its huge 75,000-gallon tank.
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History of the H.L. Hunley Submarine
The H.L. Hunley was a Confederate submarine built in 1863 during the American Civil War. It was made by Park & Lyons, along with Hunley, McClintock & Weston. The submarine was about 39.5 feet long and 3.83 feet wide. It could travel at about four knots, which is about 4.6 miles per hour.
The Hunley was powered by a hand-cranked propeller. It had a crew of one officer and seven enlisted men. For its weapon, it carried one spar torpedo. This torpedo was attached to a long pole at the front of the submarine.
The Hunley sank three times during its short life. The first two times happened during test runs. The final time was during its attack on the USS Housatonic. The Hunley was lost in the Charleston outer harbor until 1995. It was finally brought to the surface in 2000.
The Attack on the Housatonic
On February 17, 1864, the Hunley made history. It attacked the Union ship Housatonic outside Charleston Harbor. The Hunley used its spar torpedo, which was filled with 135 pounds of gunpowder.
The submarine rammed the Housatonic to stick the torpedo into its side. Then, the Hunley backed away. A rope connected to the torpedo's fuse tightened and set off the explosion. The Housatonic sank very quickly. Sadly, the Hunley was too close to the explosion. It was also badly damaged and sank shortly after.
Finding and Recovering the H.L. Hunley
The H.L. Hunley was found in 1995. It was about four miles off Sullivan’s Island in the Charleston outer harbor. Divers had to go down 30 feet underwater to find it. The submarine was buried in sand and mud.
There is some debate about who first found the Hunley's exact location. Famous author Clive Cussler says his team discovered it in 1995. Underwater archaeologist E. Lee Spence claims he found it in 1970. However, he did not confirm his discovery by diving at the spot back then.
In 2000, the Hunley was carefully lifted from the ocean. It was then sent to the Lasch Conservation Center. This center is located at the old Charleston Navy Yard. The remains of the eight crewmen who were on board when the Hunley sank were found inside. They were respectfully buried on April 17, 2004. The burial took place at the Magnolia Cemetery in Charleston.
The recovery and conservation of the H.L. Hunley was strongly supported by South Carolina Senator Glenn F. McConnell. He asked Warren Lasch to help raise money and manage the conservation work. Lasch agreed in 1997 and became the chairman of the Friends of the Hunley group.
What Damaged the H.L. Hunley?
The H.L. Hunley spent over a hundred years underwater. This caused several types of damage, or "deterioration," to its metal body.
Rust on the Submarine
Rust forms naturally when iron or steel is in water and exposed to oxygen. It can also happen when the air around metal is very wet. Since the H.L. Hunley was made of iron and was underwater for so long, rust formed all over it.
To stop more rust from forming, conservators keep the H.L. Hunley submerged in a special water tank. This keeps it away from oxygen in the air. They will keep it in the tank until a full plan for its conservation is ready.
Metal Fatigue and Cracks
Metal fatigue means the metal gets weaker over time. This can be from stress or corrosion. Stress fatigue happens when metal is pushed or pulled repeatedly. For example, water pressure can cause this. Over time, tiny cracks can form in the metal.
Corrosion fatigue happens when these cracks get worse because of rust or other chemical reactions. This makes the structure even weaker. So, normal wear and tear can lead to metal fatigue.
How Salt Water Caused Damage
The combination of salt water and metal can cause different types of corrosion. One type is electrochemical corrosion. This happens because metal particles attract other substances. Then, the salt in the water attacks the metal.
Another type is anaerobic corrosion. This occurs when certain deposits, like sulfates, surround the metal underwater. These deposits can produce hydrogen sulfide, which corrodes metal. Since the H.L. Hunley sank in the salty Charleston harbor, the salt water had over a hundred years to eat away at the metal.
Damage from Air and Oxygen
Iron objects recovered from the sea are very sensitive to air. They can quickly get worse when exposed to oxygen. Chlorides, which are chemicals from seawater, get deep into the iron. When the iron is wet, these chlorides don't cause problems. But when exposed to air, they slowly dry and form crystals. As these crystals grow, they push on the metal's surface. This causes the metal to expand and flake off. Eventually, the object can turn into a pile of iron oxide dust, which is just rust.
Concretion: A Protective Layer
Concretion is a hard, crusty layer that builds up on objects submerged in water. It's made of sand, sediment, and shells. Over time, tiny sea creatures attach to the metal and create layers of calcium. These layers form a barrier. This barrier creates a tiny, special environment on the metal's surface.
Treatments to Save the H.L. Hunley
Experts are using several methods to save the H.L. Hunley from further damage.
Timeline of Conservation Work
- August 2000: The Hunley is lifted from the sea.
- February 2001: Some parts of the hull (the submarine's body) are removed.
- March 2001: The first small objects (artifacts) are found inside.
- April 2001: The first human remains are uncovered.
- September 2001: The second big step of conservation begins.
- January 2002: The third step begins, including studies on the human remains.
- 2003: The fourth step begins, digging out the ballast tanks.
- 2008: A 3-D scan of the outside surface is made.
- June 2011: The Hunley is carefully turned upright.
- May 2014: The Hunley is placed into a 75,000-gallon tank. This tank is designed to remove salt from the metal.
- 2014-2015: The hard outer layer of concretion is removed.
- 2016: Work begins to remove the concretion from the inside.
Rotating the Submarine Upright
When the Hunley was brought up from the ocean, it was at a 45-degree angle. This was done to keep everything inside from shifting or falling through weak spots. The submarine had been lying at this angle on the seafloor for over a hundred years. To lift it, several slings were attached underneath. Then, it was slowly raised from the water.
Once at the Lasch Conservation Center, the Hunley stayed in its slings at the 45-degree angle. This allowed experts to remove hull plates and clean out eleven tons of mud and sediment from inside. They also checked the submarine's strength. After the checks, it was safe to move. In June 2011, it took three days to slowly turn the submarine upright. Conservators used sensors to make sure the weight was evenly supported.
Removing the Concretion Layer
When the Hunley arrived at the conservation center, it had over 1,200 pounds of concretion on its outer hull. In some places, this hard layer was more than an inch thick. To remove it, conservators spent many hours carefully chiseling it off. They used special air-powered chisels.
It took over a year to remove all the concretion from the outside. Now, conservators are working on the inside. This will take at least another year, maybe longer. They have to work in the small, tight spaces inside the submarine. Removing the concretion helps researchers understand why the Hunley sank. It also helps them see if holes found in the hull were from the attack on the Housatonic.
Submerging the Hunley in a Tank
After the Hunley was recovered, it was placed in a huge 75,000-gallon tank. This was done to protect it from oxygen, which would cause it to rust quickly. If left in the open air, it would start to fall apart very fast.
By putting the Hunley in the tank, filled with water and a solution of sodium hydroxide, conservators gained time. This time allows them to plan the full conservation process. The Hunley is constantly watched while in the tank. When the chemical bath has absorbed enough salt from the submarine, it is drained and replaced with a fresh solution. This process is expected to take about 5-7 years. It will be repeated until the salt level in the iron is low enough for the Hunley to be safely removed from its delicate state.
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