A massive shipping vessel recently learned that small manufacturing issues can lead to huge amounts of damage.
In 2022, the containership Maunalei, owned by transportation services company Matson, was transiting the Pacific Ocean on the way to Portland, Oregon when the crew intentionally shut down the main engine due to problems in the controllable pitch propeller system. The ship lost propulsion and subsequently lost more than 1,600 gallons of hydraulic oil. No one was injured but the damages to the vessel were calculated at more than $3 million.
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Now the National Transportation Safety Board has released the findings of its investigation and placed the blame for the accident on a propeller blade that did not meet manufacturer design specifications.
The NTSB said a third-party examined the 5-bladed propeller and found the cracks and fractures at the base of the number four blade. The cracks extended out from the bolt hole counterbore radius and were attributed to high cycle fatigue. That early degradation was blamed on a failure to meet engineering, material and chemical composition standards.
Amazingly, the bolt hole counterbore radius was only 0.2 millimeters smaller than the required size, but it was apparently enough to cause serious problems. The blade also did not meet materials specifications for impact toughness, tensile and yield strength or percent elongation, and the silicon content exceeded the specified minimum, according to the report.
It may have been an isolated incident since the other blades all met manufacturer specifications and the blade manufacturer has since revised the internal radius requirements for seven-bolt hole counterbores to improve fatigue fracture resistance. But that’s likely little comfort to Matson.
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