Maintenance Error Caused $2.2M Marine Accident

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According to the National Transportation Safety Board, The incorrect installation of a single set screw led to the loss of propulsion control  causing the ship to strike a pier at 6.8 knots. Contact between the self-unloading bulk carrier and a pier associated with the Soo Locks, in Sault Sainte Marie, Michigan, resulting in $2.2 million in damage.

Incident

The self-unloading bulk carrier was transiting the Upper St. Marys River, west of the Soo Locks, in Sault Sainte Marie, Michigan, with a crew of 25. As the vessel’s speed reduced to 3.8 knots about 0.5 miles from the end of the west center pier, the captain ordered full astern to slow the vessel further. At this point, the captain noticed that the CPP pitch indicator was “erratic,” fluctuating from full ahead, to full astern, to zero, and then back to full astern. He also received a pitch differential, or wrong-way, alarm, indicating that the requested propeller pitch from the helm station did not match the propeller’s actual pitch. He called the engine control room (ECR) to report the inconsistent pitch indicator.

The chief engineer went to the CPP control valve assembly in the lower engine room. Chief engineer called the captain from the ECR. He reported that the OD box had experienced a failure and that the main engine had to be shut down to stop the shaft from rotating. With approval from the captain, the chief engineer stopped the main engine from the ECR.

While on approach to the locks and attempting to slow, there was a propulsion problem involving the vessel’s controllable pitch propeller (CPP) system. The vessel subsequently contacted the west center pier at 6.8 knots. Before reaching the lock gate, the vessel’s motion was halted, and the crew moored the vessel to the pier. No pollution or injuries were reported. Damages to the vessel ($1,633,000) and pppier ($573,000) were estimated at $2.2 million.

Investigation

  1. The National Transportation Safety Board determines that the manufacturer’s requirement to use thread-locking fluid during installation of the feedback ring locking pin set screw on the vessel’s controllable pitch propeller system, which led to the failure of the controllable pitch propeller’s oil distribution box.
  2. There was a delay between the onset of the propulsion problem and the order to stop the engine.

Lesson learnt

  1. Loss of propulsion control in a critical phase of operation demands crewmembers act quickly to mitigate potential accidents.
  2. Emergency procedures should be well understood and practiced by crewmembers both on the bridge and in the engine room.

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Source: ntsb.gov

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