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August 12, 2010

Software could provide temporary fix for ferry vibration problems

Officials with the Washington State Department of Transportation Ferries Division say that changes to software controlling the propeller system on the new Chetzemoka ferry may provide a temporary solution to vibration issues first discovered last month.

Additional sea trials are scheduled for the middle of next week after representatives of the propulsion-control company write software exerting greater control over the engine "ramping," which allows the bow propeller to slow the ship as it approaches the dock.

The goal is to ramp up the propeller speed over a period of a few seconds longer, as opposed to a more sudden and quick thrust of power.

"The good news is that we have identified software changes that may prevent the engine from overpowering the propeller used to stop the vessel," said David Moseley, assistant secretary of the Washington State Ferries. "These new operating guidelines could allow us to operate the Chetzemoka safely and reliably while we continue working to permanently resolve the vibrations."

If the sea trials show that the propulsion-system changes eliminate the vibrations and also meet the required standards for stopping distances, Moseley said decisions will be made on when to schedule the inaugural launch of the 64-vehicle ferry between Port Townsend and Coupeville. The planned first sailing on Aug. 29 was postponed when excessive vibrations were discovered.

"The whole purpose of sea trials, which we began in late July, is to test every system on a new boat to ensure that it can operate safely and reliably," Moseley said, noting that sea trials and extensive analysis over the past week have helped eliminate internal components of the drive train, such as engine mounts and couplings and the gearbox, as causes of the vibration.

The state continues to work with Todd Pacific Shipyards, builder of the vessel, as well as the vessel design firm and other marine experts to resolve the vibration issues before formally accepting delivery of the Chetzemoka.


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