Drifting toward the Chesapeake Bay with a motor that has just stopped unexpectedly for the second time in a half-hour, Robert Jensen seems unfazed.

"I think it's fuel-starved," he says nonchalantly.

Jensen, a retired Navy engineer and former tour-boat captain, thrives on unpredictability. Setting out late that morning, the man whom local residents call "Capt'n Bob" -- a title he takes seriously -- barks to a cigar-smoking friend he calls his "associate" to "deploy the chairs," or in lay terms: Unstack a few of the dirty plastic chairs in the corner of the 17-foot boat.

It can be hard to take the sometimes-raunchy 78-year-old seriously. But Jensen, who is wearing a Mickey Mouse tie and Lance Armstrong-like wraparound sunglasses, could not be more earnest about the topic that has obsessed him for the past decade: oysters, and his plan to save them.

Now, for the first time, people are starting to listen.

Thirteen years after the eccentric Capt'n Bob persuaded Virginia officials to let him build an elaborately designed artificial reef on the bay floor using more than 3,000 tons of concrete slabs from a bridge repaving project, his dream that oysters would take hold on the reef seems real. Scientists have taken their first look, and some say they are bowled over.

"He might have one of the bay's largest healthy oyster reefs. . . . I'm a little hesitant to say until we finish our testing, but I personally feel it is a major advance," said Romuald N. Lipcius, a marine conservation biologist at the Virginia Institute of Marine Science.

Last month, Lipcius took a research team out with a crane and barge contractor to pull up part of a Jensen reef system and take samples of the age, weight and number of oysters.

"If it does show, as we feel, that there are high oyster densities, this will foresee a major change in how we do business in oyster restoration," Lipcius said.

Word of the May 27 trip has spread quickly among scientists, watermen, industry researchers and bay advocates -- people who mostly have ridiculed Jensen and his project over the years as he turned up at public hearings and, using a trailer-truck, lugged models of his reefs to lab parking lots for viewing.

Private and public interests have poured millions of dollars and millions of baby oysters overboard in mostly failed efforts to grow healthy oysters in the bay. The oysters are especially important to the bay because they clean the water.

Overfishing triggered a slow decline in oysters a century ago, but starting in the 1970s, the industry was seriously hit by disease. Growth and industrial runoff have compounded the problem. The bay's oyster population is about 1 percent of what it once was, putting out of business all but 10 or 15 of the hundreds of oyster-shucking houses that existed a decade ago, according to the Virginia Marine Resources Commission.

Families that didn't simply pack up and leave have shifted to selling ice and bait, or try to make the most of the few oysters they catch, sometimes selling them breaded and frozen to stores and restaurants.

Some scientists and state marine officials say they are excited by what they have heard about Jensen's three reef systems, which are made of huge stacks of concrete slabs laid out in concentric circles. The design is meant to raise oysters off the silty, oxygen-starved bottom and give them something hard to attach to and porous enough to allow nutrient-rich water to flow through. Most other efforts to build artificial reefs have tried to duplicate authentic oyster reefs by using ground-up oyster shells or have not been constructed to allow water -- and thus food -- to pass through.

Still, others in the oyster world are skeptical of Jensen's claims.

"There is nothing changed out there as far as any silver bullet," said James Wesson, head of the department that focuses on oyster restoration at the Virginia Marine Resources Commission.

Wesson says he believes too many factors are involved in producing healthy oysters -- factors that others have tried to replicate in some form -- to credit Jensen's project. He is among those who believe too much time has been wasted trying to save the native oyster as the bay chokes and oysters, and their predators, die. He says he advocates bringing in Asian oysters, which have proved more resistant to the diseases that kill the native Eastern oyster, and says the East Coast is "in the Dark Ages" compared with parts of the world that simply replaced their indigenous oysters when they became scarce.

Maryland and Virginia are experimenting with importing Asian oysters, but many scientists say introducing foreign plants or animals into an environment can cause major ecological damage.

Margaret Bevans Ransone, director of Bevans Oyster Co. in Kinsale, Va., one of the biggest oyster houses on the East Coast, also is unimpressed. "It's important . . . to understand that many projects have succeeded at first and then failed," she said.

In fact, the industry has reason to be cautious, having experienced so much heartbreak and failure in recent years. Some experts feel a pall pervades the industry.

"I think people are skeptical because after 10 or 15 years, we don't have huge successes to show for our investments," said Jack Travelstead, chief of fisheries at the Virginia Marine Resources Commission, which is the management agency for the state's waterways. "There is a skepticism of anyone who is going to try and do something like this." But Jensen's reef "sounds exciting," he said. "His persistence paid off."

Jensen is driven to make his mark. He says two wives divorced him because of "what they called [his] self-centeredness." He also lost a riverside home to a legal fight with his sister, and several projects failed, including a tour boat for school trips and a 56-foot canoe-carrying boat for bay cleanup projects. His eyesight is failing, and all he has now is this little dive boat with its dead engine and his dreams of cleaning the Chesapeake.

"He's a real entrepreneurial dreamer," said Richard Hoffman, a marine contractor in Howard County. "I think you could call him a pioneer in his ideas and his methods."

Hoffman says he has pumped thousands of dollars into Jensen's reefs since 1992, when Hoffman's McLean Contracting Co. won the bid to repave the Norris Bridge over the Rappahannock River and "this eccentric crazy man" asked whether he could have the used concrete. It was cheaper for McLean to just dump the concrete right there, so Hoffman agreed. He has since built casts for reproducible reefs that Jensen designed, and last month he paid the $2,500 bill to haul up one of the reef pieces.

Although he seems unable to stick to one topic of conversation for long, Jensen describes himself as focused and sharp and as having "the mind of an engineer." He lives in a rented studio, but sees himself as having limitless financial potential. As his boat drifts beneath the Norris Bridge, he looks up and calls the structure "the source of all my current wealth." He sees a group of three of his friends meeting in a 7-Eleven parking lot as the Rappahannock Preservation Society and describes a potential political force.

"I am at the apex of my life," he said in an earlier interview.

After 28 years in the Navy -- both overseas and inside the Beltway -- he became an "environmental activist." Now, he says he is fueled with ideas -- if only he can find the funding. His dream: 20 $20 million boats on the bay, vessels that would teach young people about the water and put residents to work; hundreds more reefs made from the mold he designed; and a device to count oyster larvae, he says.

The next day, his engine dies -- first in the middle of a two-mile expanse on the Rappahannock, then in a narrow inlet where a small marina happens to have an empty slip. The boat drifts in.

"I am Mr. Outside," he said. "I am a maverick. But I am the last man standing."

An abandoned oyster-shucking house in Lancaster County, Va., is among hundreds that have not survived the bay industry's decline.