Insufficient tightening of a bolt during an engine overhaul on the Ferry led to a catastrophic engine failure with expensive consequences, according to a National Transportation Safety Board (NTSB) report.
Incident
In the April 22, 2021, incident, the ferry No. 3 main suffered a failure that saw components from the engine ejected and a fire breaking out in the ship’s main engineroom.
The ferry, a 1998-built, 460.2 foot long car/passenger ferry was on a sea trial in Puget Sound when the incident occurred. Though no injuries or pollution were reported, the vessel incurred nearly $3.8 million in damages.
The NTSB report says that, in November 2020, the ferry was taken out of service for maintenance. During the maintenance period, two of the diesel-electric ferry’s four main diesel engines, numbers 2 and 3, were overhauled by factory-trained technicians. In February 2021, following the completion of engine overhauls, the vessel crew conducted engine tests. Alarms activated for the No. 3 main engine.
Crew members found pieces of a cigarette lighter in the lube oil system. Technicians returned to inspect the engine and recover the pieces; they advised ferry it was acceptable to run the engine.
On April 22, 2021, while the vessel was conducting a post-maintenance sea trial, the No. 3 main engine experienced a connecting rod assembly failure and ejected components that breached the crankcase, resulting in the ignition of hot pressurized gases that were released in the engineroom.
The crew of the ferry effectively contained the spread of the fire by stopping all fuel supply and ventilation to the engine room and isolating the space.
Probable cause
The NTSB determined the probable cause of the mechanical failure of the No. 3 main engine was a connecting rod assembly that came loose and separated from the crankshaft due to insufficient tightening (torqueing) of a lower basket bolt during the previous engine overhaul.
“When installing fasteners, personnel should use a calibrated torque wrench, follow the manufacturer’s recommended tightening guide and torque values, and verify that all required torque requirements have been completed,” the report said. “Undertorqueing a fastener may cause excess vibration or allow the fastener to come loose, while overtorqueing may lead to failure of the fastener or the machinery component being secured.”
The NTSB has previously investigated other casualties caused by improperly torqued fasteners, including an engineroom fire aboard the cruise ship in 2015, a fire aboard bulk carrier in 2016 and an engine failure on the offshore supply vessel in 2017.
Lesson learnt
“The NTSB has investigated several recent casualties that likely were caused by a failure to tighten fasteners on marine engines to the manufacturer’s recommended torque settings,” says the report.
“Undertorqueing a fastener may cause excess vibration or allow the fastener to come loose, while overtorqueing may lead to failure of the fastener or the machinery component being secured. When installing fasteners, personnel should use a calibrated torque wrench, follow the manufacturer’s recommended tightening guide and torque values, and verify that all required torque requirements have been completed.”
Containing engine room fire
“Enginerooms contain multiple fuel sources as well as mechanical ventilation, making the spaces especially vulnerable to rapidly spreading fires,” says the report.
“The crew of the ferry effectively contained the spread of a fire by removing fuel and oxygen sources. Vessel crews should familiarize themselves and train frequently on machinery, fuel oil, lube oil, and ventilation shutoff systems to quickly act to contain and suppress engine room fires before they can spread to other spaces and/or cause a loss of propulsion and electrical power.”
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Source: marine log
