After gathering support, funding, and technical capability, the American Civil War Submarine H. L. Hunley (1863-1864) and its crew of 8 returned to the surface on August 8, 2000 as part of a sizable effort. Upon recovery, Hunley was immediately brought to the Warren Lasch Conservation Center (WLCC) in Charleston, S.C to be excavated in a controlled environment. This paper will detail the inherent problems of handling a large and unstablel2-meter long iron submarine atter 136 years of marine corrosion and will focus on the use of impressed current cathodic protection technologies.
The H.L Hunley submarine was known as a Confederate "Secret Weapon". On February 1864 it became the world's first successful attack submarine after sinking the USS Housatonic, the largest ship in the Navy's blockade of Charleston. Not until World War I would another submarine sink an enemy ship. The hand-cranked Hunley submarine and its crew, however, never returned from their successful mission (Figure 1). A team led by adventurer Clive Cussler located the lost submarine and in 1996 the H.L Hunley was formally identified 1. The iron hull was found buried under several feet of sediment. Reclaiming the H. L. Hunley intact from the sea floor was a daunting and carefully controlled task placed under the responsibility of Dr. Robert S. Neyland, Head of the Naval Historical Center's Underwater Archaeology Branch. In the 1960's, a disastrous attempt was made to recover the USS Cairo from the Yazoo River near Vicksburg 2. Great care would be taken to ensure the H. L. Hunley did not meet a similar fate. Marine engineering services to devise a means of safely recovering the ship were provided by Oceaneering International, Inc. It was already known that the Hunley's hull weight had not been historically recorded and that the vessel was apparently filled with tons of compacted marine sediment ~. The goal would be to raise the ship intact, without damaging the hull or losing its contents. The added weight of sediment, and the unknown condition of the riveted hull plates was of the greatest concern. Previous underwater examinations had fotmd the vessel to be entirely covered with a very tough and strongly adhering concretion, the hull was in apparent good condition 1. Further studies conducted in November of 1999 found that some rivets had completely disintegrated, although the plates seemed in good shape. During the excavation of the submarine prior to raising, the 15 foot long iron spar, which originally held the torpedo, was found still attached to the bow. There was concern that it would be very unpractical to keep this item in place without exposing it to considerable damage. A decision was therefore made to fred a way to separate it from the submarine. The iron spar happened to be bolted down to the front cast-iron bow piece and much to everyone's amazement, the divers were able to unscrew the nut after 136 years of marine corrosion. This was testimony that the submarine had remained in the low oxygen mud. Dissolved oxygen values as low as 1.9 ppm had been measured close to the Hunley excavation site using a YSI 600XLM Multiprobe. The recorded value is just an indication of the low level of oxygen in the water column close to the sediment but more anoxic conditions were likely to exist underneath the concretion covering the metal or inside the submarine itself 3 A lift frame was designed that would be positioned over the entire hull as it lay on the sea floor. SPecial straps would then be strtmg under the hull, as the sea floor around the ship was excavated. The straps were provided with polyurethane foam filled bladders that were inflated to form fit the hull. Positioned on approximately 12-inch (30.5 cm) c
