NTSB published its report on a dangerous engine failure aboard the ferry Wenatchee after an overhaul in 2021. When an undertorqued bolt rattled loose, the engine threw a conn rod and half of a piston through an inspection cover, starting a fire and causing millions of dollars of damage.
The incident
In November 2020, the Wenatchee was taken out of service for maintenance. The vessel was drydocked for hull inspection and painting, various steel repairs, propulsion shaft seal renewals, and repair of worn propulsion shaft bearings. During the maintenance period, the nos. 2 and 3 diesel engines, upon reaching operating-hour maintenance requirements, were overhauled by factory-trained technicians in accordance with manufacturer’s guidelines.
According to their company, the rebuild was completed in standard fashion, and the technicians did not report any issues throughout the overhaul.
On April 22, after running all four engines at idle, the Wenatchee departed the WSF Eagle Harbor Maintenance Facility for the sea trial with all four engines and drive motors running. The planned route of about 50 miles for the sea trial in Puget Sound was to head south to Point Defiance after departing Eagle Harbor, then north to Kingston, and afterward south to return to Eagle Harbor.
Shortly after departing the pier, engine loading according to the trial plan began at 25% as the vessel headed south toward Point Defiance. At 0955, the
Wenatchee changed course, began traveling north, and, about 25 minutes later, the engine load was increased to 50%. Later, at 1135, the engine load was increased to 75%.
The vessel’s speed was increased to bring the engine loads up to 100% as the vessel headed south. A few minutes later, a drive motor tripped offline,
and the crew found all its fuses blown. The vessel was slowed down for troubleshooting. The staff chief engineer determined further inspection was needed shoreside for the drive motor controller and requested to return to Eagle Harbor for investigation and repairs.
Using the three remaining propulsion motors, the engine loads were brought back to 100% as the vessel transited toward Eagle Harbor. At 1331, an oiler near the watertight door between the engine rooms observed white smoke in the no. 2 engine room near the no. 3 engine and saw “red glowing items that was just popping out of no. 4 [main engine].”
Deck and engine crewmembers took action by starting a fire pump and stretching out hoses on the car deck. To isolate the no. 2 engine room from oxygen and fuel, crewmembers closed all watertight doors, stopped ventilation fans, closed ventilation fan dampers, and closed all fuel valves from tanks feeding the no. 2 engine room.
Three deck crewmembers donned firefighting gear and reported to the car deck to monitor boundaries. Two engine crewmembers also donned firefighting gear, verified all hatches and doors were closed in the fidley (the space above a vessel’s engine room extending into its stack, usually comprised of grated decking that allows for ventilation), and monitored the boundaries for heat. Crewmembers estimated that isolation of no. 2 engine room took about 2–3 minutes, and several crewmembers stated that most of their monthly training drills were similar to this scenario.
Engineers shut down the two propulsion motors in the no. 2 engine room, isolated the switchboard, and shifted the entire vessel’s electrical load and controls to
the no. 1 engine room. Firefighting water was not used, as fire teams reported boundaries to be cool to the touch, and other crewmembers observed the smoke to be dissipating as the fire extinguished itself. Based on this, engineers determined it was unnecessary to discharge the vessel’s fixed CO2 fire extinguishing system.
At 13:50, the captain requested that the vessel be towed back to Eagle Harbor. About 30 minutes later, a Seattle fireboat arrived alongside, and two firefighters
boarded the Wenatchee. The firefighters met with crewmembers in the EOS and observed the smoke to be dissipating in the no. 2 engine room. Two tugboats arrived at 1435 and began towing the Wenatchee toward Eagle Harbor. At 14:47, the fire was reported out.
About 16:30, Wenatchee moored at the Eagle Harbor Maintenance Facility. Firefighters from the Bainbridge Island Fire Department, a senior port engineer, and
a marine chemist boarded the vessel, verified the no. 2 engine room was safe for entry, and entered the space with the staff chief engineer to assess the situation. Engineers inspecting the affected engine room found a broken connecting rod, part of a piston, and an inspection cover laying on the deck outboard of the no. 3 engine. Inside the engine, part of the piston had fallen down and was resting on top of the crankshaft.
Probable cause
The National Transportation Safety Board determines that the probable cause of the mechanical failure of the no. 3 main engine aboard the passenger vessel Wenatchee 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 recent engine overhaul.
Lessons learned
- 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. 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.
- Engine rooms contain multiple fuel sources as well as mechanical ventilation, making the spaces especially vulnerable to rapidly spreading fires. The crew of the Wenatchee 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.
EXPLORE MORE AT NTSB’S REPORT ON WENATCHEE
