NTSB: Propeller blade flaw led to containership Maunalei losing propulsion
Written by Marine Log Staff
The National Transportation Safety Board has issued its report on an August 2022 incident in which the 681 foot, 1,992 TEU Matson Navigation containership Maunalei incurred $3 million in damages after a propeller blade cracked, leading to a loss of hydraulic oil and propulsion while transiting the Pacific Ocean.
The NTSB investigation found that a blade on the vessel’s controllable pitch propeller system did not meet manufacturer design specifications.
The Maunalei was traveling to Portland, Oregon, from Anchorage, Alaska on Aug. 11, 2022, for drydock repairs when the crew intentionally shut down the main engine due to problems in the controllable pitch propeller system, resulting in a loss of propulsion about 245 miles from the entrance to the Columbia River near Portland. The vessel’s controllable pitch propeller system may have lost up to 1,632 gallons of hydraulic oil.
On drydocking the Maunalei, a classification society surveyor found the cracks and fractures at the base of the no. 4 blade of the 5-bladed propeller, where the blade was bolted to the propeller’s hub. The cracks initiated at the blade’s bolt hole counterbore radius and were consistent with progressive cracking due to high cycle fatigue. The class society found the no. 4 blade did not meet manufacturer design specifications for engineering, material and chemical composition. The bolt hole counterbore radius was 0.2 millimeters smaller than the required 0.8 millimeters. It did not meet materials specifications for impact toughness, tensile and yield strength or percent elongation, and the silicon content exceeded the specified minimum.
Investigators found the crack and fracture that developed on the no. 4 blade was likely an isolated occurrence, as the blade did not meet specifications and a manufacturer’s analysis of other five-bladed controllable pitch propeller systems on similar vessels did not identify any other instances of cracks.
Following the Maunalei‘s loss of propulsion, the blade manufacturer revised the internal radius requirement—enlarging it—for all seven-bolt hole counterbores to improve fatigue fracture resistance.
- Full details in the NTSB report. Download it HERE
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