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Fieldwork

USGS Assists in Recovery of the Civil War Submarine H.L. Hunley


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H.L. Hunley in lifting sling
Recovered: The H.L. Hunley in the lifting sling.
The Confederate submarine H.L. Hunley carved its name in history 136 years ago by being the first submarine to sink a ship. The Hunley sank for unknown reasons on February 17, 1864, after successfully ramming a spar containing a 90-lb black powder charge into the wooden hull of the Federal Union blockade ship USS Housatonic. The Housatonic was destroyed. Submarine engineer Horace L. Hunley built the sub, which was only 4 ft in diameter, 40 ft long, with 16-inch-wide conning towers and was powered by a hand-turned crank operated by the crew.

The Hunley had sunk twice before. The first time, five men died and four escaped. The second time, eight crewmembers perished, including the inventor. The third and last time, the Hunley went to the bottom with a crew of nine aboard. Novelist Clive Cussler had located the submarine in 1995 near the tip of the north jetty at Charleston Harbor about 4 miles off Sullivans Island, SC.

Members of the St. Petersburg Field Center (SPFC) staff assisted the National Park Service, South Carolina Institute of Archeology and Anthropology, and U.S. Naval Historical Center in their quest to raise the sub for historical and archaeological preservation (Fig. 1). The SPFC staff involved were Mark Hansen, Nancy Dewitt, Dana Wiese, Bo Suthard, and Dave Bennett. Archeologists were also interested in the submarine's fateful victim but the Housatonic was too fragmented for recovery.

Drawing of the Hunley
Artist rendering of the sub (courtesy of Friends of the H. L. Hunley). Note conning towers at top and rudder end at right.

The USGS provided geological expertise to archeologists to help reveal the structure of the sediment layers around the Hunley and the Housatonic and to understand the submarine burial sequence. This information was crucial for planning purposes that would ultimately lead to successful resurrection and preservation of the historic submarine.

In May 1999, the USGS scientists collected chirp (high-resolution) seismic and 500-kHz sidescan data adjacent to and over the Hunley and Housatonic wreck sites from aboard the SPFC's R/V G.K. Gilbert. Five 20-ft-long sediment cores were collected within a distance of 25 ft from the Hunley and three cores were taken near the Housatonic site. The cores were used for groundtruthing seismic data, and a local engineering firm analyzed the sediments for geotechnical properties. Geotechnical properties were needed to assess the bearing capacity of the underlying sediments during the excavation and raising process.

USGS personnel with Clive Cussler
Left to right: Bo Suthard, Mark Hansen, Nancy Dewitt, Clive Cussler, and Dana Wiese.
Mark Hansen theorizes that the historical morphologic changes of the Charleston Harbor ebb-tidal delta are important for explanation of the Hunley's burial sequence. Tidal-flow patterns and shape of the ebb-tidal delta were radically altered when 19,000-ft-long jetties were constructed at the mouth of Charleston Harbor in 1890. Prior to jetty construction, the majority of Charleston Harbor's 2.2 billion ft³ tidal prism flowed through an S-shaped main ebb-tidal channel that runs from Fort Sumter south along Morris Island, then directly eastward at Lighthouse Inlet. During this time, tidal currents near the Hunley site were estimated to be low, ~1-2 knots. Jetty construction dramatically changed tidal-flow patterns by diverting the main ebb-tidal channel and tidal flow directly east, to a location 300 ft from the Hunley site. Measured current flows on the Hunley site now are 4-5 knots.

The Hunley went down on the eastern flank of the then existing ebb-tidal delta, which consisted of fine to medium sands. Tidal currents were relatively low, consequently minimal scouring and subsequent settling occurred, resulting in the submarine being fully exposed on the seafloor. Twenty-five years after the sinking, the jetties induced strong tidal currents over the ship, resulting in rapid scouring and settling. The scouring/settling process continued until contact was made with a firm Pleistocene clay layer, at which point settling ceased. This sequence and time frame are confirmed by biofouling studies that indicate the submarine was exposed on the seafloor surface for only 15-20 years. We suggest that the ship's rather rapid burial into anoxic deltaic sediments helped preserve the sub by slowing the oxidation rate.

After two years of intensive geotechnical analyses, engineering, and planning, recovery efforts began in March 2000. The Hunley was successfully raised from the ocean floor on August 8th and was returned to Charleston for preservation. The USGS scientists were invited to witness the raising, partake in the celebration, and meet with Clive Cussler. It will take months just to figure out how to access the interior of the sub without damage. It will take 5-10 years to excavate the sediment-filled interior, remove the crew's remains and any associated artifacts, and preserve the vessel. After restoration, the submarine will be on display at the Charleston Museum in Charleston, SC. The journey of the H.L. Hunley is now complete.


Related Sound Waves Stories
CMG Researchers in St. Petersburg Receive Senate Commendation
March, 2000

Related Web Sites
Friends of the Hunley
official site

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