(FORTUNE Small Business) – We're 50 miles off Florida's Atlantic coast, and things aren't going well. A deep-sea recovery device the size of a Hummer is floating in the water alongside its 250-foot-long mother ship, the Odyssey Explorer. In a few days the contraption is supposed to descend to a shipwreck some 1,700 feet below the surface and perhaps retrieve up to $75 million in gold coins from a site that has yielded at least that much already.

But the submersible, a remotely operated vehicle (ROV), refuses to sink because its new foam flotation collar is too buoyant. Crew members haul the ROV out of the water, attach around eight 40-pound lead weights, and try again. No luck. The ROV bobs like a cork. They add all their remaining lead and try again. Still not enough. Finally one of the technicians has an idea: A half-dozen crewmen race below, return with big round iron weights from the barbell sets in the ship's crude gymnasium, and wire them in place. The ROV is lowered overboard yet again. Its electric motors spin, and it sinks gently into the deep. "It worked!" declares Andrew Craig, 31, the short, thin, perpetually worried-looking Irishman heading the exploration.

There is something to be said for spending 12 years searching for a sunken treasure. For one thing, it gives you lots of time to think. Time to come up with clever solutions for a million unpredictable setbacks, like diving machines that don't sink. Even better, time to imagine what you'll do with all that loot the day it arrives, wet and glistening, from the ocean floor.

And while most of us would spend that dozen years dreaming of nonstop parties, mansions, and sports cars, the two guys who started Odyssey Marine Exploration did something far less obvious, particularly in the swashbuckling world of treasure hunting. Greg Stemm and John Morris devised a business plan.

Essentially, Stemm and Morris have set out to build a predictable, sustainable, and (dare we say) corporate business in an industry traditionally dominated by maverick wildcatters. They want Odyssey to be a company that finds gold as routinely as Exxon finds oil. "When we show that these [discoveries are] repeatable, the image of this business will change," Stemm says. "The oil companies were exploration companies when they started, but once they got big enough and predictable enough, that changed."

When he began, Stemm's biggest fear was winding up like Mel Fisher and Tommy Thompson. Both explorers found fabulous wrecks in the 1980s, then spent a decade snared in costly legal battles with governments or with insurance companies that had covered the original loss when the ships went down and were entitled to a share of the finds. "We decided early on that we'd only pursue wrecks without disputed claims or strike a clean deal with the owners right away," says Stemm.

So they raised venture capital, sold shares to the public (Amex symbol: OMR), and started methodically combing archives for likely wrecks and striking deals with insurance companies and governments that held title to their cargo. It wasn't hard to figure out how to do it right, says Stemm, 47, a bearded, hyperkinetic former PR executive who wears flannel shirts and dungarees and carries a Civil War-era gold coin worth $10,000 in his wallet. "We just watched all the mistakes other explorers made."

In late 2003 their planning began to pay off. At a site 100 miles off the coast of Georgia, Odyssey crews hauled up thousands of gold and silver coins, ingots, bottles, jars, and decorative porcelain from the S.S. Republic, a paddle-wheel steamer that went down in a hurricane back in 1865 en route from New York City to New Orleans. When it sank in 1,700 feet of water, the Republic reportedly carried some $400,000 in coins earmarked for the reconstruction of the South. But those coins, especially the gold ones, are now worth far more than their face value. A single gold piece can fetch anywhere from $3,000 to over half a million dollars, depending on its rarity and condition.

The company declines to estimate the total value of the hoard, but independent coin collectors say it's probably worth upwards of $150 million. So far, though, less than a quarter of the coins have been found. Stemm figures the missing coins were probably in pursers' safes, which were common on ships of that era, and might have plunged to the ocean floor before the rest of the ship hit bottom.

No one knows for sure whether the safes contain silver coins, bullion, or far more valuable gold coins. The good news: Odyssey gets to keep whatever it finds. In January 2004 the company paid $1.6 million in compensation to the Atlantic Mutual Insurance Co., which had insured some of the Republic's original cargo. "Within two months of raising the coins, we were able to put them on the market and start turning them into cash," says Morris. Odyssey's years of planning also started to pay off in the form of television specials, museum exhibitions, books, marketing programs, and more exploration, all designed to leverage the original discovery.

How, you wonder, does someone get into the shipwreck biz? Stemm worked in the public relations business for years--Bob Hope was one client. Stemm wound up owning a successful advertising and PR shop in Tampa, handling hotel and tourism companies. Morris, 56, was a real estate developer who built shopping malls in the Midwest and Florida. The two, who met through Stemm's wife, Laurie, became friends, and learned that they both loved messing with boats.

In 1986, at a bar in the Caymans, a ship broker told them that a college was selling its 85-foot exploration ship. They bought it sight unseen for $100,000 and docked it in Tampa. "First it was just a great place to have a gin and tonic and watch the sun go down," recalls Stemm.

But then Stemm and Morris saw a demonstration of an underseas-exploration device and decided to get into the business of leasing the ship to research scientists and treasure hunters. In 1988, with some financial backing from family and friends, they started to do some treasure hunting of their own and went looking for a potentially valuable wreck near the Florida Keys. In 1989 they found the wreck but little treasure. "I decided we had to get serious about it," says Morris.

The search for the Republic took 12 years and $2 million. "There were days that were uncomfortable because we had no money," says Stemm. "When we found the gold, we weren't awestruck," he says. "It was just plain relief. I could exhale." Finally Odyssey could implement the business plan that Stemm and Morris had been refining for so long. After 17 years of preparation, as the saying goes, the company was an overnight success.

Some things are different now, though. At lunch in a Tampa restaurant Stemm starts to mention how much money Odyssey will make in the current quarter. Morris reminds Stemm that the company's earnings are confidential because they haven't yet been announced to shareholders. Stemm is briefly chastened. "I guess I'm not used to having earnings," he confesses.

The first step after the Republic's treasure landed was to get some cash in the bank. "We recognized a long time ago that gold and silver aren't money," says Morris, a serious, lawyerly type who nevertheless sometimes strolls around the office in boat shoes. "It's inventory that has to be turned into money."

Once they knew what they had found, Stemm and Morris booked a hotel room at a national numismatics show in Florida and invited a handful of coin experts to visit. "One after another, we had ten of the world's best coin dealers passing through our room, telling us the best way to market the coins," says Stemm. Odyssey hired one firm to clean and mount the coins in ways that would preserve their value. (A tiny scratch can slash the value of a mint-condition gold coin.)

Odyssey is in no rush to unload its inventory. So far, only $15 million of its $75 million in found coins have gone on the market. The company started off by striking deals with a half-dozen dealers to quietly offer some of the gold coins to their top clients. Stemm says they turned down an offer of $300,000 for one coin. "We sold it when the offer rose to over $500,000," he says.

Marketing silver coins is a different business. They are cheaper, of course, but also attract a different kind of buyer. "People who buy gold coins are typically numismatists seeking to fill out a collection," explains Stemm. "People who buy silver coins are less likely to be completing a collection. They want a piece of history."

To attract history buffs, Odyssey's staff researchers have devoted considerable effort to fleshing out the story of the S.S. Republic, a ship that was captured by both Union and Confederate forces during the Civil War before it sank. Company brochures describe some of the Republic's 92 passengers as adventurers eager to invest in the rebuilding of postwar New Orleans. One was a black man who apparently filed one of the earliest and most important antidiscrimination suits in federal court. Odyssey's researchers even tracked down the relatives of a passenger whose photo adorned a locket found in the wreck.

Silver coins from the Republic, mounted in plastic cases and delivered in a wooden box, complete with a written history of the ship and a commemorative DVD, sell for $1,000 to $10,000. Don't have ten large to spare? The company is selling thousands of the bottles, jars, and porcelains it found too. They go for upwards of $500, but bargain hunters can buy a lump of the Republic's coal, attractively boxed, for $100.

The PR-savvy Stemm turned down 20 proposals from producers who wanted to do television specials about the discovery of the Republic. Instead he struck a revenue-sharing deal with National Geographic, which has produced two lengthy television specials on the Republic. And he micromanages the company's marketing efforts. Every word of every piece of promotional material has been written, read, or edited by Greg Stemm. "I drive the creative people crazy," he says with an unabashed grin. Stemm insists, too, on owning or controlling distribution of every photograph or video of his ships, the wrecks, and the treasure. The shots are intellectual property that is valuable to Odyssey's bottom line and its public image, he asserts. "I cut my teeth working with the Bob Hope organization," says Stemm. "I assure you, they controlled everything. And who had a better image than Bob Hope?"

Stemm and Morris must be doing something right. Last year Odyssey earned $5.3 million on revenues of $15.9 million. (The company's market cap is currently around $100 million, and the total retail value of what has been recovered from the Republic so far will probably exceed $75 million. The value of the unrecovered coins could be several times that.) But the partners have bigger plans. More than three years ago, when Odyssey had only five employees and hadn't yet found the wreck, it hired George Becker, 70, a tourist industry veteran who had built Sea World into a major attraction. Becker's job? Creating a treasure museum or park in Florida and two traveling shows that will tell the story of shipwreck exploration in general, and the S.S. Republic in particular. He plans to sell coins, ship replicas, and other collectibles at the attractions, which he figures can pull in as many as a million visitors a year.

Stemm views the tourist attractions and the gradual sale of the coins as part of his effort to portray shipwreck explorers as legitimate businessmen. That continues to be an uphill battle. No securities analysts cover Odyssey, and that limits investor interest. Stemm figures Wall Street views the business as too risky and unpredictable to forecast. He is eager to change that perception. "If we take assets, reinvest them, and are successful many times, then we can go to analysts and say it's repeatable," he says.

He laments that Odyssey has few competitors. "It would be good if there were more companies," he says. "It would make us look more like an industry." And Stemm's research indicates plenty of sunken treasure to go around. "We think there are 3,000 good wrecks out there," he adds. "If we do one a year, it will be a long time before we run out of targets."

To boost the odds of finding more profitable wrecks, Odyssey's researchers are combing through maritime archives in the U.S. and abroad. "We have people poring through libraries all over Europe," says Stemm. Odyssey has even dispatched agents to seaside towns around the Mediterranean with instructions to chat up fishermen who might have snagged something promising in their nets. "We offer fishermen half-a-million dollars for a lead that turns into a successful find," he explains. "We also buy them a lot of beer."

Word of Odyssey's interest has paid off. In the early 1990s, a historian rummaging through the records of a French spy learned of a British warship, the Sussex, that sank near Gibraltar in 1687. It was said to be carrying nine tons of gold, intended to bribe the Duke of Savoy to join forces against France. The historian quietly tipped off Odyssey, which told the British government. If the Sussex search is fruitful, the researcher will get a flat fee. Until then, he will remain unidentified and is sworn to secrecy.

The Sussex treasure could be worth billions. In a deal with Britain, Odyssey gets about half of the first $500 million and 40% of anything above that. Stemm thinks Odyssey's explorers have located the wreck, but Odyssey isn't stopping there. "I want the research department to have a fluid list of top-ten targets," says Guy Zajonc, the company's chief legal officer, who negotiated the deal with Britain.

Of course, Odyssey hasn't quite become a staid, predictable company like Exxon or Shell. A graph of Odyssey's share price on the Amex resembles the North Atlantic in a bad storm. OMR was 10 cents in late 2000. The shares shot up to nearly $7 in early 2004, after news of the Republic find hit the market, then fell to around $2.40, where they have remained. Odyssey's $100 million market cap approximates estimates of the Republic's recovered treasure but ignores revenues from the attractions business and any future finds, including the Sussex. At the very least, investors in Odyssey can claim some link to white-knuckle stories of wild adventures at sea. And who knows? They might even get to run their hands through sunken treasure someday.