A fault in an ageing CPP servo unit control board may have led to a 1992-built 3,206 dwt oil and chemical tanker making sudden and uncontrolled sternway and contacting with a lock gate in Antwerp. The unit, which was below the engine room bottom plates next to the propeller shaft, showed signs of heat damage.
The MAIB preliminary report says: “Stolt Petrel was berthed port side alongside, 150m ahead of the lock gate. The propeller, controlled from the port bridge console, was turning at 130 RPM with the propeller pitch set to zero. The berthing pilot embarked and joined the master, who was alone on the bridge.
“Just after the mooring lines had been let go, the master heard the engine pitch change, saw that the engine pitch indicated full astern, and heard the manoeuvring alarm sound. The master attempted, without success, to regain control of the pitch from the wing and centre bridge consoles, following which the chief engineer attempted to alter the pitch from the control room. Being unable to regain control of the propeller pitch, the master then pushed the emergency stop button to shut down the main engine.
“As the vessel gained sternway the master ordered both anchors to be let go. The third officer, at the aft mooring deck, ran a mooring line ashore and made it fast; however the line parted.
“Stolt Petrel made contact with the dock gate at 3 knots, causing extensive damage to her stern and minor damage to the lock gate.
“Extensive testing could not identify with certainty the reason for the propeller operating astern. However, the most likely cause was the intermittent failure of the 17 year old CPP servo unit control board. The board, which was located below the engine room bottom plates adjacent to the propeller shaft, showed evidence of some heat damage.”
Since the incident Stolt Tankers BV has replaced the CPP control board and actuator arm on board Stolt Petrel and her sister vessels, and disseminated the conclusions from its investigation into this accident to its fleet.
MAIB’s Chief Inspector has recommended that Stolt Tankers BV review the controllable pitch control system on board its vessels to ensure that the risks of similar system failures are identified, and the effects of their failure are mitigated. He has also “strongly advised” the company to review the operation of main engines while alongside, particularly when operating in fixed RPM mode as well as bridge manning requirements when manoeuvring in port.
MAIB is also concerned about the attempt to make a mooring fast onshore and says that Stolt should “Ensure that all crew are aware of the risks of parting mooring lines, and the need for good communication between the master and crew at mooring stations.
The company should also “ensure that accidents are reported to MAIB in a timely manner and that potential evidence, including VDR data, is preserved”.