French and U.S. experts are searching for a 17th century ship they believe sank in Lake Michigan in 1679.

Three French underwater archaeologists are diving at a site near Poverty Island, where expedition leader Steve Libert believes the Griffin sank. He discovered a wooden beam jutting from the lake bottom in 2001.

Scientists say the beam appears to have been there for centuries, an important finding as they try to determine whether it's part of the Griffin.

Marine archaeologists from the U.S. and France are studying the timber and digging a pit beneath it  to see if it's attached to a buried ship. They said Tuesday a probing device has detected what appears to be a solid surface up to six metres (20 feet) below the lake floor.

They say they're not certain they're dealing with a shipwreck. But Michel L'Hour of France's Department of Underwater Archaeological Research says the timber appears to be a bowsprit, a pole that extends from a vessel's stem.

The search has stirred excitement in the Michigan community of Fairport, where about 40 experts and support crew members were camped by the lake.

Commercial fisherman Larry Barbeau's boat is the offshore nerve center for the expedition seeking the Griffin, the first ship of European design to traverse the upper Great Lakes. It was built on orders of legendary French explorer Rene Robert Cavelier de la Salle.

French and U.S. experts insisted it was too early to say whether the site was a shipwreck. But anticipation was building at the prospect of solving a puzzle more than three centuries old.

"After we get done for the day, everybody calls or comes to the house and they're like, `What did you find? What did you see? Can you tell me anything?' "Barbeau said in an interview Sunday aboard his ship, which holds crucial expedition equipment, including "umbilical" cables that supply oxygen to divers. 

Archaeologists Rob Reedy and Misty Jackson sit on the Viking and sift through material that was found in the sediment, watching for artifacts — "anything man-made" that would help identify a ship, Reedy said.

Thus far, the only candidate has been a slab of blackened wood about  38 cm (15 inches) long with characteristics suggesting it might have been fashioned by human hands. Its origin remains unknown.