A trial to introduce mini-capesize type ships at the Port of Weipa went badly wrong when a tiny crack in a cooling system caused a main engine to fail, leading to a loss of propulsion and a vessel grounding right across a main shipping channel.
It was a combination of luck and competent seamanship by tug crews that prevented the port from being blocked for months upon months and thereby devastating the local economy of far north-eastern Australia.
An investigation by the national accident detective, the Australian Transport Safety Bureau (ATSB), has concluded that the risk of engine failure during departure had not been fully considered. The pre-trial simulations did not include contingencies such as loss of propulsion and steerage that would have helped in working out the risk and planning for it.
Consequently, tugs were not present to help the ship when propulsion was lost. The ATSB also concluded that tug masters had not been trained in the “specifics” of escort towage or emergency response. The investigator did, however, conclude that the actions of the marine pilots, ship’s crew and tug masters “were timely and significantly reduced the consequences.”
Backgrounder: the Orient Centaur
The Orient Centaur (IMO: 9464572) is a 114,841 deadweight dry bulker. Deadweight refers to the weight-carrying capacity of a ship and it is expressed in metric tonnes. The ship had a length of 255.5 meters (838 feet) while the ship access channel, which runs in an east/west line, had a maximum width of about 106 meters (348 feet), according to the official passage plan.
This is a key point to note – the ship was longer than the width of the channel.
On the day of the accident, November 6, 2017, the ship was outbound under the guidance of harbor pilots from the Port of Weipa, Australia, with a destination of Hong Kong. The journey was significant because it was part of a trial to see how ships of that size handled in the port.
Orient Centaur was fully laden with a cargo of bauxite (a type of rock from which the metal aluminum is extracted). Weipa, which is operated by North Queensland Bulk Ports Corp. is a major export facility for bauxite and it handled about 27.3 million metric tonnes (30.14 million U.S. tons) in the 2018-2019 financial year. That quantity of bauxite is larger than the annual production volumes in many countries.
At 15:15 the normal pre-departure checks began and two harbor pilots boarded the ship. Two tugs were on hand, the Peter Crooke and the SL King.
The ship began to move with the high tide at 16:10 when the tugs pulled the Orient Centaur off the berth. By 16:43, the ship released both tugs from their duties and they began to head back to berth. The ship then carried on through the channel as planned at a speed of eight knots (10.36 miles per hour).
At 17:16 the first alarm sounded for the main engine, followed by low-pressure and high-temperature alarms. The chief engineer phoned the bridge and asked the master to stop the main engine for repairs. One of the pilots advised the master that a slow speed was acceptable. He also advised the chief engineer that the ship could not be stopped because it was in narrow channel.
At 17:17 the main engine’s automatic-slowdown activated. The chief engineer called the master to report the problem and the communications pilot broadcast a general call to all tugs for help.
At 17:18 the main engine shut off. But the ship was still traveling at about 8.6 knots (9.9 miles per hour). Without power, the ship began to drift.
The communications pilot was making radio calls to the main vessel traffic controller at Weipa stating that “the ship has lost the main engine, taking a steer” and that the ship was about to run aground.
The ship began to turn to starboard (the right-hand side of the vessel as it travels in a forward motion) and it grounded on the northern wall of the channel. Unfortunately for the Orient Centaur, that was only the first grounding it was to have that evening. With the forward starboard side wedged on the northern wall of the channel, the stern of the ship began to swing across the port’s access channel.
A perilous position
Both the SL King and the Peter Cooke began to race back to the scene – and a race it was as the ship had left on the high tide and the water level would shortly begin to fall. At 17:59 the stern of the ship ran aground on the southern side of the access channel.
The Orient Centaur was now blocking the whole channel and, being wedged from prow to stern across a narrow channel with a falling tide, the ship was in a position of peril.
“There was then a significant risk the ship’s structural integrity could be compromised and at that time, the pilots estimated they had about 30 minutes to refloat the ship,” the ATSB reported.
A debrief note by a variety of interested parties spelled out the consequences if the ship had broken up.
“This could have blocked the channel and essentially closed the Port of Weipa. Due to the potential complexity of the salvage and also the remote location and long transit times for suitable salvage equipment this could have led to a salvage and port closure lasting many months,” the note reads.
Fortunately, the tug SL King arrived at 18:05 and started holding the ship’s stern and, by 18:10 the Peter Crooke arrived. With the ship’s crew putting an anchor in the water at the starboard prow, the SL King and the Peter Crooke were able to pull the stern of the ship away from the wall of the channel. The ship refloated at 18:20. The SL King changed position to sail ahead of the Orient Centaur with a long-line attached to the center part of the ship’s prow.
By 18:30 the ship was back in the center of the channel with the SL King towing, the Peter Crooke on the port quarter and a third tug that had responded to the situation, the Harry Evans, on the starboard quarter. The three tugs were able to steer the ship to an emergency anchorage and the ship was officially detained pending further inspections.
By 22:06 all three tugs cleared the ship and the incident was effectively over.
The ship was later checked and found to have only minimal superficial damage. The Orient Centaur was allowed to proceed to China a few days later.
During the incident, the ship’s engineers had identified that part of the cooling system for a cylinder head in the main engine had cracked. The crew who were in the engine room at the time saw water coming out of the crack. The loss of that coolant water caused overheating that triggered the automatic shutdown of the main engine.
The manufacturer of the engine had previously, in January 2014, issued a service letter about the cooling water systems on the type of engine used by the Orient Centaur. The service letter said, “most cases of heavy corrosion in the cooling water system or cracked cylinder cooling jackets on the cylinder cover, were related to insufficient cooling water maintenance.”
In summary, so-called “heavy deposits” tended to find their way between the cylinder cover and the cooling jacket. This causes extra stress and, potentially, cracking. An inspection also found that the crack ran through a hole that was present for the purpose of securing a bolt. “An area of inherent stress concentration,” the ATSB said.
The investigator concluded that the main engine shut down due to “low cooling water flow and a loss of propulsion”.
Risk assessment and simulation failures
The ATSB noted that the hazards of engine failure and associated loss of propulsion had been considered in advance and that having tugs present mitigated that risk. But releasing the tugs before the ship had cleared the channel meant that “there was no effective mitigation against grounding.”
During the investigation, pilots told the ATSB that while they had been trained in simulated emergencies involving a loss of propulsion and steerage, this had only been on much smaller ships in less confined areas. Loss of propulsion and steerage for ships of the size of the Orient Centaur had not been simulated for the very tightly confined South Channel.
ATSB inspectors attended a computer simulation workshop after the event and observed two simulations of the grounding: one with help from tugs and one without. In the simulation with tugs, the ship was “kept directionally stable and its speed reduced significantly, to control a grounding.” In the other scenario, the ship grounded uncontrollably.
“The inclusion of a loss of propulsion simulation in a confined channel during the mini cape-size approval process would have informed the likelihood of grounding and the subsequent impact on port operations and provided the opportunity to practice the response to such an event,” the ATSB reported.
The managers of the ship, Interorient Marine Services, now have the cooling water tested onboard every week and at a laboratory once every six months.
All pilots and tug masters have completed a variety of emergency tugs and towage scenarios while arrival and departure briefs have been updated.
All ships over 200 meters in length (656 feet) now have an escort tug “made fast” (i.e. secured with a line) from when the ship leaves the wharf until the ship exits the South Channel. Two much more powerful tugs are also now based at the Port of Amrun, about 25 miles southwest-by-south and 60 minutes sailing time from the Port of Weipa.