The 2006-built container ship, Maunalei, lost power as a result of a flawed propeller blade on a voyage between Anchorage and Portland in August 2022, according to a US National Transportation Safety Board (NTSB) investigation. The NTSB revealed its findings yesterday, concluding that the vessel’s controllable pitch propeller had failed to meet design requirements.
On her way to a drydocking in Portland, the 1,992 teu ship’s controllable pitch propeller failed, resulting in a loss of propulsion some 245 nautical miles from the entrance to the Columbia River, close to Portland. The vessel’s propeller system is thought to have lost more than 1,632 gallons of hydraulic oil and resulting damage has been estimated at $3m.
Unlike fixed pitch propellers which are cast in one piece, controllable pitch props are designed with blades bolted to the hub. In this case, the NTSB concluded, the manufacture of the propeller was substandard. Cracks and fractures at the base of the fourth blade in the five-blade propeller failed to meet specification requirements and did not meet requirements for impact toughness, tensile, or yield strength.
The NTSB investigators concluded that the blade damage was probably an isolated incident: analysis of other five-bladed props on similar vessels indicated no problems. However the blade manufacturer has adjusted the specification to improve propeller fatigue fracture resistance.
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