On April 22, 2021, a catastrophic engine failure on a 460-foot-long passenger and car ferry near Bainbridge Island near Washington started a fire that caused more than $3.8 million in damages.
On March 14, 2022, the National Transportation Safety Board concluded its investigation into the incident and tied the fire aboard the Wenatchee to an improperly tightened fastener. A single nut.
The fire occurred during a sea trial in Puget Sound after the fastener failure led to components from the engine being ejected and causing a fire in the engine room. Luckily none of the 13 crew members were injured, and their swift action prevented it from being worse.
The issue dates back to November 2020, when the Wenatchee, operated by Washington State Ferries, was taken out of service for maintenance. During maintenance, two of the four main diesel engines were overhauled by factory-trained technicians.
In February 2021, crew conducted engine tests following the overhauls. Alarms went off in the No. 3 main engine, and crew members found pieces of a cigarette lighter in the lube oil system. The maintenance technicians returned, drained the oil and searched the lube oil system for two days. They recovered about 70% of the cigarette lighter's plastic and metal components and told Washington State Ferries that it was fine to run the engine. However, none of the engines were run again until the vessel headed for a sea trial.
In April, during the post-maintenance sea trial, the connecting rod assembly in the No. 3 main engine failed and ejected components that breached the crankcase and ignited hot pressurized gasses. The crew contained the fire by stopping all fuel supply and ventilation to the engine room and isolating the space. One crewmember witnessed "fire, smoke, and debris flying everywhere."
Engineers examined the lube oil system to see if the cigarette lighter could have caused the engine failure. While they found parts of the lighter throughout the system, they found nothing that would suggest the lighter parts started the fire.
The NTSB found that the probable cause of the mechanical failure was the connecting rod assembly that came loose due to insufficient tightening (torqueing) of a lower basket bolt during the previous engine overhaul. The NTSB stressed that maintenance technicians should use a calibrated torque wrench in compliance with the manufacturer's recommendations and verify that all required torque requirements had been completed.
This is not the first time that improperly torqued fasteners have caused problems. A fire aboard the Carnival Liberty cruise ship in 2015, a fire on the Nenita bulk carrier in 2016 and an engine failure on the Red Dawn offshore supply vessel in 2017 were all traced back to bad fastening, according to the NTSB.
The Wenatchee was built in 1998 and can carry up to 202 vehicles and some 1,812 passengers, so it could have been much worse. All because of an "engine assembly error," or nut that had not been properly torqued.
The operator cooperated with the investigation, provided recommendations to prevent future incidents, and is designing and installing a video camera system with fire and smoke sensors for the Wenatchee and other vessels in its class.
Editor's Note: The headline has been updated to reflect that it was a failed fastener and not a defective fastener that likely caused the fire.