Thursday, February 08, 2007


Side-scan sonar used to find shipwrecks


The Cincinnati Post

February 08, 2007

COLUMBUS - The George Dunbar left Cleveland at 6 p.m. on June 29, 1902, bound for Alpena, Mich.

Loaded with coal, the 136-foot ship rode low in the water as it steamed northwest into rough Lake Erie weather, her boilers running full steam.

By nightfall, the Dunbar struggled past Kelleys Island, the wind and waves pulling at her seams. In the darkness, the ship began to take on more water than her crew could pump out. To lessen the strain, the Dunbar's skipper turned his ship into the wind.

But she already was lost. At 4 a.m., her hull split.

The skipper, his wife and daughter escaped the Dunbar, but seven crew members were lost to Erie, which has claimed an estimated 2,000 ships.

The Dunbar has survived more than a century of summer squalls, November gales and winter ice, and the shipwreck remains preserved 45 feet below the surface, just over the international line in Canadian waters.

In 2003, Dale Liebenthal cruised over the wreck and took a ghostly picture of the ship, still heavy with coal, revealing her stern, bow and bulwarks. Her smokestack lies broken, about 40 feet off the port stern.

Liebenthal led a team of state Geological Survey scientists in a pilot study using a tool called side-scan sonar to produce images of 25 shipwrecks around Kelleys Island and the Bass Islands to the west.

Their work, just recently published because of budget cuts, helps the Ohio Department of Natural Resources comply with a state law that orders the agency to inventory, evaluate, protect and designate underwater shipwreck locations.

Archaeologists and historians say they need this information to conserve wrecks as well as provide information to divers and the general public. Side-scan sonar produces images similar to aerial photography, but at an oblique angle.

Geologists already use the sonar to study the lake's bottom. Distinguishing between sand, mud and rock provides insights into fish-spawning areas, beach erosion and mineral production.

"We come across things using the sonar all the time. We wonder if they're ships," Liebenthal said.

The side-scan sonar is lowered into the water on a brace attached to the bow of the division's 25-foot research launch.

It operates just below the surface by bouncing sound waves off the lake bottom. Images are produced as the boat is slowly piloted in a series of precise, calibrated runs over wreck areas.

The sound echoes are recorded in shades of black and gray, depending on how reflective and hard a target is. Scientists look for the straight lines and angles that might indicate a hull or superstructure. Some images are more obvious than others.

The western basin of the lake is fairly shallow, and the waters around the islands are popular with recreational divers. Some wreck sites have been similarly scanned with sonar by private diving clubs.

Still, Lake Erie remains almost totally unexplored. Ohio waters alone contain an estimated 600 wrecks.

"We're pretty far behind in terms of other Great Lake states," said Charles E. Herdendorf, a geologist and archaeological diver who served as a consultant on the study. "The Canadians are way ahead of us in mapping their shipwrecks and opening them up for diving."

The islands area is particularly rich in wrecks, thanks in part to two shoals north of Kelleys Island. Herdendorf estimated that as many as 50 wrecks might litter the lake bottom around the islands.

"If ships got hit by storms, they could easily hit the shoals," said Constance Livchak, a Geological Survey scientist working on the project.

And many did.

Nineteen of the 25 wrecks in the study surround Kelleys, and eight of those went down on the rocks. Only the general locations of most shipwrecks are known. One purpose in searching them out was to fix their exact positions, because wrecks can move with time and the elements. Ice, in particular, acts like a bulldozer.

"The ice covering the lake cracks and grinds together, pushing up and down ... and then it scours the bottom," Liebenthal said.

Five wrecks were recorded on Gull Island Shoal, but the sonar failed to find much of anything left.

Around the islands, wreck sites can be close together. A ship's identity can be uncertain even when sonar reveals a vessel.

For example, images recorded off the northwest shore of Kelleys show either the Oak Valley or the L.B. Crocker.

Sonar also can reveal why a ship went down. The C.H. Plummer, which burned at its dock in 1888, probably was lost to a boiler fire and not to the spontaneous combustion of its cargo of lime, Herdendorf said.

"Where the coal was stored is the only place in the shipwreck where the fire had burned completely through. The rest of the shipwreck was intact," he said. Carrie Sowden, a marine archaeologist with the Great Lakes Historical Society in Vermillion, said she plans to use the data to plan dives at the sites.

Sowden said she wants to confirm wrecks as well as help create dive charts of the lost vessels.

"We'll go out (with volunteers) and see if we can locate them. It could be a shipwreck, a pile of rocks or ballast. It could be anything," she said. "We can learn something about the ship, its construction and maybe why it sank."

Sowden has dived at six wreck sites in the past two years, including the Dundee, a 200-foot schooner barge that went down in 1900 in a storm 14 miles off Cleveland.

"It was under tow. The first thing that happens in bad weather is they cut the tow line. They lost control of it. The barge had no steering," she said.

However, the biggest mystery on the lake for Sowden is one that hasn't appeared on any sonar.

In December 1909, the Marquette and Bessemer No. 2, a 300-foot ferry loaded with railroad cars full of coal, left Conneaut in a gale for Port Stanley. The ferry was never heard from again.


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