Citizen oversight group seeks on-water performance tests, winch upgrades, for Prince William Sound tanker escort tugs
The Prince William Sound Regional Citizens' Advisory Council is recommending on-water tests and other measures to make sure the Sound's escort tugs are sufficiently powerful and stable to prevent catastrophic spills from the loaded oil tankers they accompany.
The recommendations came in an April 6 letter from Mark Swanson, the council's executive director, to Alyeska's Ship Escort/Response Vessel System, which contracts with Crowley Maritime to operate the tugs. The recommendations result from a council-commissioned analysis of the tugs by Det Norske Veritas, an independent Norwegian foundation dedicated to improving the safety of merchant vessels.
Besides urging on-water tests and other measures to evaluate the tugs' performance, the citizens' council recommended upgrades to the towline winches already installed on the tugs.
The council, Swanson wrote, "strongly encourages the adoption of these recommendations…to bring the safety and equipment of the escort tugs used in the Sound…up to date with internationally accepted best practice."
Each loaded oil tanker traveling in Prince William Sound is escorted by two tugs. The escorts can help prevent catastrophic accidents like the 1989 grounding of the Exxon Valdez. They can also start the cleanup if prevention fails and a spill results.
One issue raised in the Det Norske Veritas analysis and in the council's letter is the need to make sure the escort tugs can perform safely and effectively in what is called "indirect mode."
Tugs commonly apply force to a larger vessel by means of a towline attached to the tug's stern, and the Prince William Sound tugs are rated by the American Bureau of Shipping for this type of service.
But the escort tugs in the Sound tugs can also apply force by turning sideways and acting as a brake or drag to slow a tanker down. This is known as "indirect mode." They have not been rated for indirect service.
"As a tug's speed increases and towing forces move off the centerline, mechanical power become a secondary factor in determining the safety of a tow," Swanson wrote. "The implications of a tug saving or assisting a tanker while in indirect towing mode need to be recognized."
A copy of the council's letter is transmitted with this news release. Additional materials—including the Det Norske Veritas analysis—are available online at:
Posted: April 16, 2012