At night on the rolling black Atlantic, the boat exploring the sunken remains of the Andrea Doria looks like a science fiction outpost.

The low deck is covered with bright yellow and orange machinery that illuminates the boat in a yellow glow. The machines, pressure chambers and elongated air tanks and generators tremble and churn. The yellow diving bell waits poised on the stern. The Sea Level II is an exploratory vessel both anachronistic and modern, evoking both Jules Verne and Jacques Yves Cousteau.

At the rail, wife beside him, is the leader of the expedition, Peter Gimbel. He is well over six feet tall and wears high rubber boots over jeans. His wife, actress Elga Andersen, wears seashells in her hair.

Waving to a visitor, they look, despite Gimbel's gray hair, like a comic-book adventure couple, a tableau.

You will have to get much closer to see that Andersen wears, behind her ear, a medicated bandage that is an antidote to seasickness, to which she is prone. You will have to get much, much closer to learn that she has always been opposed to this expedition.

Gimbel has come to it -- an expedition in which he once nearly died -- not for riches, because he is already rich, not for simple adventure, but because he is obsessed with the Andrea Doria and can't let go.

The Andria Doria has rested at the bottom of the sea 25 years now, since the July night when, in heavy fog, it was struck by the Swedish liner Stockholm 50 miles off Nantucket, Mass., and sank with a loss of 50 lives.

Almost since that time it has been, in a sense, Peter Gimbel's wreck. He was, with a diving partner, the first to explore the wreck, going down one day after the liner sank.

He has, since then, made more than three dozen dives, photographing the ship for Life magazine and making a television documentary, "The Mystery of the Andrea Doria," five years ago. The documentary posed questions about the soundness of the liner: why did the Andrea Doria, which was supposed to be unsinkable, sink 11 hours after the collision and why did the owners, shortly before the ship's engineers were to testify at a pre-trial hearing, suddenly decide to settle out of court?

The answer, Gimbel suggested in the film, was a possibly missing watertight door. But he was never able to prove it. On the verge of discovery, he ran out of power cable and hose and, unable to go further, was literally left hanging.

Now, he has returned -- he swears for the last time -- with an expedition of 40 to try to prove his theory about the missing watertight door.

There is also the tantalizing prospect of treasure: two safes that are thought to be on board, one holding the passenger's valuables, one from the Bank of Rome. Rumor has put the treasure anywhere from $1 million to $3 million.

Gimbel is skeptical. He would be surprised if the safes were empty, he says, but he would also be surprised if they contained $3 million. That would have inspired, he says, "a more strenuous effort to obtain it."

There is also the problem of raising the safes. They are thought to be in the ship's bank office, an area filled with silt and debris. Divers, working with suction hoses and with their hands, have so far been unable even to spot the safes, let alone raise them.

The treasures so far have been two sets of doors and dozens of dishes, fine Ginori china, with the gold leaf eroded just enough to be an eerie reminder of 25 years at the bottom of the sea.

Wether a real treasure is found does not really matter. The laws on who would own the treasure are vague. And the treasure would probably not exceed the $1.5 million this expedition has cost. Gimbel has invested much of his own money in this trip; the rest he raised personally from stockholders.

The real treasure will be the rights to the adventure, the package. If a two-hour documentary can be sold to television, says Gimbel, he will make back his costs. He and Andersen are also considering a book.

If they retrieve the safes, they may open them on live television. They know the value of television on this expedition. Consider the message Andersen has left in the galley for the crew:

"Tomorrow NBC Today Show will be coming aboard -- please wear your [Doria] T-shirts."

The first time Gimbel dove to the Andrea Doria, when he was 28, he used no diving bell. Wearing a wet suit and a large double air tank, he stayed at the wreck, which lay on its side, 11 decks high, only six or seven minutes.

The currents were swift and Gimbel's diving partner, overcome by carbon dioxide poisoning when he exerted himself at too great a depth, had to be brought to the top.

Time has not made the dive, 160 feet to the top of the hull, 230 feet to the ocean floor, less perilous. The 697-foot ship is shrouded in spots with tangled trawler nets. Sharks swim about, drawn to the sea life that grows up about a wreck.

Though the 11 decks are basically intact, much of the ship has crumbled, settling into the bottom of the wreck and creating a mass of debris. In the powerful currents, visibility is about five feet. Early last month, an experienced amateur diver looking for souvenirs died.

Gimbel, who has chartered a 196-foot supply boat of the sort used for offshore oil and mineral drilling, will not be diving free. He will, with a team of profession divers, be diving from a bell, using a technique called saturation diving in order to spend maximum time in the water. This technique houses the divers, when not in the water, in a pressurized chamber that duplicates the pressure on the ocean floor.

"Mother," the divers call the chamber. It is small, 18 by 23 feet, and can house eight men, who will remain inside a month. The interior is painted Frequency Green, a color designed to reduce stress.

At 53, Gimbel, who has never been "in sat" (saturation) before, will be the oldest man on the team. Decompression, when the project is over, will take several days. Should the bell suddenly lose pressure, the men would quite likely die.

Gimbel, on the last expedition has one close call. He experienced an oxgyen hit, a pure shot of oxygen after breathing a deep-dea diver's mix of helium oxygen. When he describes it now, his wife gets up and walks away.

"I was hanging off the down line decompressing," he says. "Suddenly the physical world went insane . . . everything was shaking, divers were upside down, I was completely out of control, very cold. . . . I had an urge, which was an absolute necessity, to tear off my mask, which I started to do. . . . The last thing I remember hearing before blacking out was, 'Haul Gimble in and undress him.' The last thing I remember thinking was, 'Either somebody is gonna save me or I'm dead. . .'"

Anderson, later and in private, gives her impression.

"Everybody was in the mess hall, but all of a sudden, I don't know why, I had this feeling to come out. . . . He was lying on his back, his eyes were open, he was unconscious, his helmet was on the floor. . . .

"I went back in the mess hall and got the [film] crew. Gimbel always told me, whatever happens, keep the cameras rolling. . . ."

She talks about this expedition, in which she is co-producer of the film.

"I did everything to discourage it. I cried, I pull all my charm . . . oh well, listen, you know. Then when I saw he really had to do it, I closed all those doors and I just said okay. . . ."

She said okay, because, finally, she had no choice.

"To me the ship is very nearly the other woman, who has the true attraction for him."

"'Department store heir,'" Gimbel says, bitterly, mimicking the way he is described in the newspapers. He is the great-grandson of the founder of Gimbel's, which has stores in New York and Philadelphia.

"I cannot stand it, I find it most distasteful. I made a film 10 years ago, 'Blue Waters, White Death,' that did reasonably well. I worked one year in the family business because it would have been too cruel to my father to not give it that much of a shot, and I'm still department store heir . . . though I am making a little progress. Now they're starting to call me 'department store heir and filmmaker. . . .'"

He says this in a quiet moment, off in the bow of the boat, where he's been answering the whys of his fascination with the wreck.

Why he went out to the Andrea Doria the first time? "The question to me is how could any qualified diver not want to see it."

Why, more curiously, he has continued going down, since, as he himself says, the expedition "has not been a lot of fun" and his wife is "scared bloody hell to death" of it?

The answer to this seems flat -- "I guess I've never felt it's been done properly," he says -- and so the talk turns back to his life, to his twin brother, who died of cancer at 29, and the 10 years they worked on Wall Street.

"Ten years I could have been in films," he says, smilingly sadly. "ybut I was very influenced by my twin, and that's where he felt we should make our career . . . maybe I was brainwashed.

"My family had been in business for generations, and my father, though he was liberal in voicing his opinions, made them very clear. . . . Everything he admired and respected had to do with success in business. . . . Actually, he admired success in all fields."

The death of his twin and a fear that he might die, as well, prompted him to leave business, to "make a life for me."

He chose an adventurer's life, though with a purpose. Gimbel, says old diving buddy Michael DeCamp, was never one to dive a pretty little wreck in the Caribbean; he required a serious project.

Gimbel parachuted into unexplored regions of Peru and wrote about it for National Geographic. He made an underwater film on Antarctic seals. He married and divorced twice and denies that the adventuring had anything to do with the disintegration of the marriages. He was not a relaxed man. He was driven, his wife Andersen insists, by a need to establish himself on his own.

"He had a powerful, successful father, and he wanted to succeed on his own, not because of the money," says Andersen.

"On target," says Gimbel, tersely.

So they've returned to the Doria. They will stay about a month, or until they raise the safes, or their money runs out. They are doing it, Gimbel can only repeat, because he feels it has not been done properly.

And should they fail, he adds, he will not return. It will be the end.

"I keep telling myself I'll never see her after this again," he says.

Didn't he say that last time?

He smiles.

"Could be."