When an improperly fastened bolt on a piston assembly backed off its nut during sea trials after being overhauled, all hell broke loose inside the engine and then inside the engine room.
The boat was the ferry Wenatchee, and the engine was an EMD 710, one of four on the 202-car Washington State Ferries double-ender and one of two in the #2 engine room. The date was April 22, 2021.
Long story short: After a cascading series of unfortunate events down by the crankcase, a piston was literally thrown out of the engine through an inspection port. Hot crankcase gases also escaped and caught on fire. White smoke was observed in the engine room while black smoke rose from the stacks.
The WSF crew did all the right things to isolate the engine room and the fire was quickly extinguished. No one was hurt, but the much-needed ferry would continue to be out of service for many more months as engines and the engine room were rebuilt. Total cost of the accident is estimated to be $3.8 million.
The initial overhaul had been performed by “factory-trained” technicians, but somebody didn’t tighten the loose bolt to the prescribed 75 foot-pounds of torque. Too much torque and the bolt breaks; too little and it vibrates loose.
The details of this incident, as reported above, are all included in a March 2, 2022, report from the National Transportation Safety Board. Amazingly enough, NTSB investigators were able to figure out exactly what happened by carefully examining the threads of the affected parts, among other things.
This loose-bolt incident reminds me of an accident in British Columbia maybe 20 years ago in which a BC Ferries boat crashed into a dock and wiped out several pleasure craft. The cause was a missing cotter pin in the throttle linkage.