Tampa, Fla. ? Explorers believe they have found the sunken remains of an 1860s steamer that could yield the richest cargo ever recovered from a shipwreck: thousands of gold coins worth as much as $180 million.

The S.S. Republic was carrying 59 passengers and 20,000 $20 gold coins from New York to New Orleans when it sank in a hurricane off Savannah, Ga., on Oct. 25, 1865, according to newspaper accounts and other historical records.

All the passengers boarded life boats and got off alive, but the coins — intended to help pay for reconstruction of the South after the Civil War — went to the bottom of the Atlantic Ocean with the Republic. An expert has estimated they would be worth $120 million to $180 million today.

After searching for 12 years, Greg Stemm and John Morris of Odyssey Marine Explorations Inc. said Saturday that they found the wreck last month in 1,700 feet of water about 100 miles southeast of Savannah.

Documentation and excavation of the site using remotely operated robotic equipment is set to begin next month. Stemm said the Tampa-based company recently bought a 250-foot ship and a special robotic “remotely operated vehicle” to carry out the project.

Odyssey, a publicly traded company founded in the mid-1990s, has a number of shipwreck search projects in various stages. Stemm and Morris have performed only one other deep-water excavation, that of a Spanish wreck in the Dry Tortugas that yielded about $5 million in gold and thousands of artifacts.

The company made headlines recently when it entered a historic partnership with the British government to excavate the wreck of the HMS Sussex, which sank in 1694 off Gibraltar while leading a British fleet into the Mediterranean Sea for a war against France and its leader, Louis XIV.

Historians believe the 157-foot warship was carrying nine tons of gold coins aimed at buying the loyalty of the Duke of Savoy, a potential ally in southeastern France. The Sussex’s cargo could be more valuable than the Republic’s, but Odyssey will have to share it with England: The company will get 80 percent of the first $45 million and about 50 percent of the proceeds thereafter.

The painting Tennessee