Off the coast of Madagascar early this month, Barry Clifford was doing what he’s done for most of his professional life now, swimming underwater, searching for shipwrecks and artifacts and encrusted treasure buried beneath centuries of silt.
The Provincetown explorer has long believed he’s found one of history’s most famous pirate ships, William Kidd’s Adventure Galley, which specialists have concluded lies near the island nation off the southeastern coast of Africa.
Professional underwater archeologists are not sure this is Kidd’s ship. So expeditions like the one Clifford was conducting continue.
Early this month, after exploring other nearby wrecks, Clifford headed for where he believes Captain Kidd’s cabin is, in a ship that sank in 1698.
“Everything’s winding down,’’ Clifford recalled during an interview in his cavernous workshop in Brewster. “I’ve been there 10 weeks. So I said I’m just going to go on a little adventure, just like looking for frogs when I was a little kid.’’
Clifford’s detector was buzzing, signaling metal — and lots of it — nearby. He moved large stones that began to collapse slightly, revealing a small chamber.
“I spent a couple of days moving mud and the whole pit was hot, everywhere I put my detectors,’’ he said. Presently, he felt something Mother Nature does not produce: a right angle of wood.
“Then: boom! The whole thing caved in on me. Something glanced off my head and hit my arm. My air was just about out, so I left the pit and came back in really quietly so I wouldn’t disturb anything, and there’s this big silver bar sitting on the bottom.’’
Big is right. The silver bar weighs 110 pounds. Clifford believes it’s part of Kidd’s treasure. If he’s right — and historians are, so far, withholding judgment — the man once called the “Pirate Prince’’ will have done it again.
“Treasure is not gold and silver, it’s the artifacts,’’ he said. “It’s the history. I went specifically to Madagascar to look for Kidd’s ship. The treasure of Kidd’s ship is that he’s the most famous pirate. And this is what I do.’’
Clifford, who turns 70 this week, is a former coach and physical education teacher at Bourne High School, who jettisoned that early career to start a construction and diving business.
He struck the underwater archeological equivalent of gold in 1984 when he found the fabled 100-foot pirate ship Whydah, laden with treasure and artifacts, off Wellfleet. It was the first pirate ship whose identity was verified, a discovery that fueled a passion in Clifford he’s followed around the world.
“We’re private entrepreneurs,’’ he said. “But we’ve never sold one artifact.’’
Victor Mastone, director of the Massachusetts Board of Underwater Archaeological Resources, said Clifford has followed state guidelines since the Whydah’s discovery.
“From the point of view of the standards we put forth, their field work, the conservation, the curation has met archeological standards,’’ Mastone said.
But Clifford is a lightning rod. The United Nations Educational, Scientific and Cultural Organization has expressed concern about his work off Madagascar, underscoring the need for professional archeology at the site.
Charles D. Beeker, director of underwater science at Indiana University’s School of Public Health, said most academics see it in black and white: They’re archeologists. He’s a treasure hunter.
“I deal with treasure hunters all the time, and most of them are weird, strange people who are totally in it for themselves,’’ Beeker said. “I don’t find that with Barry.’’
Beeker said that the silver bar may or may not have belonged to Captain Kidd, who was hanged for murder and piracy in London in 1701. For now, he said, it’s just powerful circumstantial evidence.
Heavy, too. Clifford said he can scarcely believe that he got hit on the head by a piece of Kidd’s treasure.
For now, he is looking for something else, this time on land. He wants a museum to permanently display all the things he’s found buried out there in the deep.