Treasure-hunter Bob Evans has spent half his life dreaming about the SS Central America, a pre-Civil War steamship decaying in the lightless depths off South Carolina. Now he’s returning to the shipwreck after 23 years.

Evans set out this week with deep-ocean explorer Odyssey Marine Exploration Inc. to revisit the remains of the 19th-century side-wheel steamer, which sank in 1857 with the loss of 425 lives and an undetermined amount of gold. Despite recovery efforts in 1989 through 1991 that netted more than two tons of gold, Odyssey says there may still be $86 million of gold lying more than a mile deep.

“This is the greatest lost treasure in United States history,” said Evans, who was chief scientist on earlier expeditions.

Even with the plunge in gold prices last year, the metal is still worth more than triple its price in the early 1990s, when previous recovery efforts were suspended because of legal battles over rights to the treasure. And the rare coins that have been found at the site are selling for much more than their weight in gold.

Chance for vindication

For Odyssey, the shipwreck is another chance to show the potential gains from deep-sea salvaging. While the Tampa-based company has recovered tons of treasure in past projects, it has failed at others.

Odyssey is a “very atypical company in an atypical industry,” said Mark Argento, an analyst at Lake Street Capital Markets in Minneapolis. “It’s more like a biotech company: Not every biotech company gets every drug approved.”

Odyssey is undeterred. “Our research department and the court-appointed experts all believe there is enough gold remaining at the SS Central America to warrant the expense of conducting an expedition,” Odyssey President Mark Gordon said.

In 1857, the quickest way to get from San Francisco to New York was to take a steamship to Panama, cross the isthmus by train and then sail up the coast. The Central America, which ran the Atlantic leg, sank on Sept. 12 after being caught in a hurricane. Only about 150 passengers were saved.

The ship was carrying a large consignment of gold from California’s Gold Rush.

The shipwreck site was located in 1988 by a group led by explorer Tommy Thompson. Evans, a geologist, had been working with Thompson since 1983.

Two hours to reach wreck

“It’s essentially a four-story collapsed building at the bottom of the sea,” said Evans.

It takes about two hours for a submersible to dive to the sea floor at the wreck site and it can stay down for days at a time, said Ernie Tapanes, a project manager with Odyssey.

During court battles, an expert estimated that the gold remaining on the ship was probably worth $343,000 to $1.37 million in 1857. Using the low end of the estimate, there may be 17,150 coins still at the site if the gold was in the form of rare Double Eagles. Using a conservative average price per coin of $5,000, the cargo could be worth $85.8 million.

Evans said he’s sure the expedition will more than pay for itself ­— though he won’t be more specific. “All along,” he said, “I’ve known what [the sunken ship] still holds.”