The U.S. Coast Guard is investigating why an unmanned tugboat sank at its dock on the Saginaw River in December 2010, encasing the top of the vessel in ice and resulting in at least 800 gallons of diesel fuel leaking into the water.
The 65-foot Ann Marie, owned by Luedtke Engineering of Frankfort, Mich., was reported sunk at the Bay Aggregates dock in Bay City at about 0800 on Dec. 13, said Lt. Justin Westmiller of Coast Guard Sector Detroit. The tug was tied up for the winter after being used in a dredging project on the river by the Army Corps of Engineers.
Westmiller said Ann Marie sank in about 25 feet of water sometime late in the evening of Dec. 12 or early the next morning. Employees of Bay Aggregates reported the sinking while making their first inspection of the yard Dec. 13.
“They had made their rounds earlier that day (Dec. 12) and nothing was reported out of place,” Westmiller said.
The tug was refloated on Dec. 17, but investigators could not immediately determine what had caused it to take on water. There were no reports of damage to the vessel before it was laid up for the winter, Westmiller said.
“We never found a cause, an easy cause, as to why it sank,” he said. “Once we pumped all the water out, she floated fine. There’s a couple of different possibilities, but we don’t want to speculate at this point. The easy explanation â€” that the hull was holed or something like that â€” it was not the case.”
Paul Luedtke, secretary and treasurer for Luedtke Engineering, said a strong storm passed through the region that weekend, but the company had not determined if that was the cause. The National Oceanic and Atmospheric Administration reported wind gusts in the area as high as 45 knots on Dec. 12.
“Right now as far as I know it’s all speculation,” Luedtke said. “There was nobody there physically watching it to see what happened.”
Eight hundred to 900 gallons of diesel fuel leaked from Ann Marie after it sank, Westmiller said. Crews from Young’s Environmental Cleanup Inc. of Grand Rapids deployed two booms to contain the spill and absorb the fuel while divers sealed the tug’s tank. Some of the fuel that leaked was locked in ice on the surface of the river.
“We recovered upwards of 300 to 400 gallons from the surface,” Westmiller said. “We also recovered quite a bit of ice that was contaminated with fuel. We cut that into sections and removed it.”
Another Luedtke tug, the 55-foot Karl E. Luedtke, was brought in to break the ice and keep the water open during the salvage operation. The company used a land crane and a derrick barge to lift the 81-ton tug to the surface after divers attached slings to its hull.