The boat is trolling not too far off the Battery, dragging what is basically a missile-shaped metal detector, when the onboard computer picks up a little blip. Something's down there.
It could be an abandoned crab trap, a long-lost anchor — or the remains of frame torpedoes set up by Confederate troops nearly 150 years ago, when this city was under siege.
James Spirek, the deputy state underwater archaeologist, means to find out which it is. He's leading an expedition by the South Carolina Institute for Archaeology and Anthropology to map one of the largest and most important battlefields in the country: Charleston Harbor.
It's being funded by a $28,000 National Park Service grant.
Even after all these years, there still are remnants of the 19th century sunk in the harbor, buried under the beach at Sullivan's Island, hidden beneath the marsh surrounding James Island.