Shipyard blames valve failure for sinking dry dock, capsizing tugboat that was insideAug 22, 2012 01:47 PM
Courtesy U.S. Coast Guard
The oceangoing tugboat Invader lies capsized inside a sunken dry dock at the Vigor Industrial yard in Seattle. The dry dock slowly took on water due to a faulty check valve.
A tugboat capsized inside a Seattle dry dock after the dock partially sank due to a faulty check valve.
The 127-foot ocean towing tug Invader, owned by Crowley Maritime, was in the Vigor Industrial yard for routine maintenance, which had just been completed.
Shipyard personnel discovered the accident at approximately 1200 on March 18. Apparently the dry dock had been taking on water and sank until it reached the seabed. As it sank, the tug capsized on its starboard side, and like the dry dock, was partially submerged.
Because it was the weekend, no one was aboard either Invader or the dry dock at the time of the accident and there were no injuries.
“A check valve failed and was obstructed with debris,” said Adam Beck, director of regional operations for Vigor Industrial. “The overboard pipe for this valve was right at the waterline. The failed valve allowed water to slowly ingress into the dock at first. As the dock heeled, the pipe became farther submerged, thus allowing the water ingress to accelerate. Unfortunately, this occurred late in the evening over a weekend so it went unnoticed.”
At the time of the accident, Invader’s tanks contained diesel fuel, lube oil and hydraulic fluid. The U.S. Coast Guard and the Washington State Department of Ecology deployed multiple layers of boom around the perimeter of the dry dock and the 7,200-hp tug to prevent the spreading of any potential leakage.
The salvage of the tug and dry dock was led by Global Diving & Salvage of Seattle, with assistance by Vigor, General Construction Co. of Federal Way, Wash., and other subcontractors.
It took six days to raise the tugboat and six more days to raise the dry dock, said Frank Immel, marketing manager for Global Diving & Salvage.
“The tug was separated from the dry dock,” Immel said. “After sealing the tugboat, pumps were used to refloat the tug whilst a heavy lift crane provided stability. On the dry dock, the existing pumping system was inoperable. New pumps had to be installed, along with venting and discharge ports. Once all was in order and all openings sealed, the dry dock was pumped out in a specific sequence and refloated.”
Once refloated March 26, Invader was relocated to Vigor’s Seattle shipyard so that the final disposition of the 38-year-old tug could be determined. The dry dock was raised on April 4.
Vigor estimates that less than 20 gallons of petroleum products were spilled in the accident. All spilled product was contained within the primary boom perimeter and recovered.Edit Module