TRAVERSE CITY, Mich. — Excited shipwreck hunters and scientists assembled in a Lake Michigan fishing village last June, hoping to solve a mystery dating back more than three centuries: the fate of a ship sailed by the 17th century French explorer Reni-Robert Cavelier, Sieur de La Salle, during a voyage of discovery extending from the Great Lakes to the Gulf of Mexico.

Team members recovered a nearly 20-foot-long wooden slab with signs of human workmanship jammed into the lake bed, but were disappointed to find no buried wreckage. The timber has been examined by U.S. and French experts and underwent a CT scan and carbon dating to determine its age and whether it once was part of a vessel.

Nearly a year later, reports obtained by The Associated Press and interviews with key players reveal sharp divisions over whether the elusive ship has been found.

Mission leader Steve Libert and others with his organization, Great Lakes Exploration Group LLC, contend the timber is a bowsprit from a ship — likely the Griffin, last seen in 1679 with a six-member crew and a cargo of furs near Green Bay in present-day Wisconsin. A report by three French underwater archaeologists says the beam has characteristics consistent with a bowsprit, or pole that extends from a vessel’s stem. It was apparently was submerged for a century or more. But it stops short of confirming a link to La Salle’s ship.

Meanwhile, two U.S. scientists who joined the expedition, project manager Ken Vrana and archaeologist Misty Jackson, say the timber is probably a “pound net stake,” an underwater fishing apparatus used in the Great Lakes in the 19th and early 20th centuries. That is also the opinion of Dean Anderson, Michigan’s state archaeologist, and Carol Griggs, a Cornell University specialist in using tree rings to determine the age of wooden objects.

“We’re not killjoys,” said Jackson, a Michigan-based cultural resources consultant. “We’d have all loved for this to be the Griffin. We’re just presenting the evidence and that data that we have, and it points away from that.”

Libert, a retired military intelligence analyst who has spent three decades and about $1 million hunting for the Griffin, scoffs at the net stake idea. He plans to continue searching this summer for shipwreck debris near uninhabited Poverty Island, where he found the timber while diving in 2001 nearly 50 feet below the lake’s surface.

“I’m 99 percent sure the Griffin is in that area and we’ll find it,” he said.

An excavation permit Libert obtained last year required his team report its findings to the state archaeologist’s office. The AP obtained the document through a Freedom of Information Act filing.

A vexing question is why the timber was found almost upright on the lake bottom, with the lower 9 feet buried in thick sediment. The report, written by Vrana and Jackson, says that supports the pound net hypothesis. Libert contends the force of the vessel’s sinking during a vicious storm could have wedged the timber into the sediment.

The report includes photographs of another reputed pound net stake found by a fisherman that has features in common with the timber Libert’s team recovered, such as peg-like tree nails protruding near one end. But there are differences: The fisherman’s slab was probably almost twice as long, and the tree nails were square while those on the Libert slab were tapered or cone-shaped.

Jackson argues that those and other differences between the beams are minor, especially given the history of net stake fishing in the area. Libert says members of Native American fishing families reaching back generations insist such stakes weren’t used where his beam was found.

Another point of contention is the timber’s age. It had too few tree rings for a definitive answer.

Griggs and Vrana contend an analysis from radiocarbon dating suggest there’s a 78 percent chance the beam came from a tree felled between 1820 and 1950. The likelihood it dated to the late 1600s is less than 5 percent, they say.

Darden Hood, president of the company that performed the carbon-14 tests, said the wood could have originated from several periods between 1670 and 1950 and attempting to narrow the time range could produce misleading results.

Both sides agree Poverty Island is a good place to search, based on writings of La Salle and his companions. But the skeptics say Great Lakes Exploration is a long way from proving it has discovered the Griffin’s resting place.

Richard Gross, staff historian with Great Lakes Exploration, says the next step is to thoroughly survey the lake bed using sonar, metal detectors and other tools for signs of buried artifacts.

“We’ve been fooled by this technology in the past, but every step in the process you learn,” he said. “We’re really encouraged by what we’ve found.”