Cracked Propeller Blade Led To Loss Of Propulsion On Containership In Pacific Ocean, NTSB Reports

The National Transportation Safety Board reported that a Matson container ship’s propeller blade cracked, causing a sudden loss of hydraulic oil and propulsion while transiting the Pacific Ocean.

The investigation discovered that a blade on the vessel’s controllable pitch propeller system did not satisfy the manufacturer’s design specifications.

The Maunalei (built-in 2006) was sailing to Portland, Oregon, from Anchorage, Alaska, on 11 August 2022 for drydock repairs when the crew intentionally shut down the main engine owing to issues with the controllable pitch propeller system.

This led to a loss of propulsion approximately 245 miles to the Columbia River from the entrance, close to Portland.

The controllable pitch propeller system of the 33,771 dwt vessel might have lost as much as 1,632 gallons of hydraulic oil.

Damages to the vessel were estimated at a whopping $3 million.

During drydocking, a third-party firm discovered fractures and cracks at the base of the no. 2 and no. 4 blades on the five-bladed propeller bolted to the propeller hub.

The cracks were discovered near the bolt-hole counterbore radius of blade no. 4.

These were consistent with gradual breaking due to severe cycle fatigue.

The company discovered that the no. 4 blade had not fulfilled the manufacturer’s design specifications for material, engineering, and chemical composition.

The bolt-hole counterbore radius measured relatively 0.2 millimetres smaller compared to the required 0.8 millimetres.

It had not met the material specifications for impact toughness, yield strength, tensile, or per cent elongation.

Besides, the silicon content also exceeded the minimum value specified.

Investigators discovered that the crack and fracture developed on the No. 4 blade was probably an isolated case, as the blade had not met the specifications.

A manufacturer’s analysis of other five-bladed controllable pitch propeller mechanisms on similar vessels did not recognize the different instances of cracks.

After losing propulsion, the blade’s manufacturer increased the internal radius requirement for the seven-bolt hole counterbores to improve fatigue fracture resistance.

Reference: NTSB

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