In one five-week salvage operation, 63 shipping containers lost overboard from YM Efficiency in June 2018 have been removed from Australia’s east coast.
Frustrated after nearly two years of inaction, the Australian Maritime Safety Authority (AMSA) contracted wreck removal marine services provider Ardent Oceania for the deepsea salvage operation.
One vessel, Pride, with 17 Australian seafarers have achieved what the shipowner said was too risky: cleaning up containers and debris from depths of more than 100 m in strong currents and low visibility.
Shipowner Yang Ming and its insurers retrieved five containers from shallow waters at the time of the disaster, but refused to remove the remaining boxes, arguing they were best left undisturbed and did not constitute pollution.
The salvage operation “recovered thousands of tonnes of waste and pollution that has mired Newcastle-Port Stephens coastal communities for almost two years”, AMSA announced at a press conference. AMSA also thanked the seafarers who worked on the operation.
Alongside the crew, underwater robotics played a key role in the operation. “The remotely operated underwater vehicles (ROV) have been vital in performing a number of tasks,” said an AMSA spokesperson.
A pilot launched the ROV from a hanger within the vessel to survey the container sites before the lift operation could get under way.
The ROV attached the lifting gear to the containers with manipulator robotic arms, removed twist locks from containers locked together, cut the boxes apart, removed all debris and pollution from the ocean floor, and surveyed the site after the lift to ensure nothing was left behind before returning to the hanger.
Pride is fitted with a built-in control room where the pilot operated the ROV’s giant arms, while watching the operation through high-definition cameras. The job site appeared on monitors and displayed the video feeds and data via a fibre-optic linked electronic control system.
One arm of the ROV is for intricate tasks requiring dexterity, the other for heavy-duty operations. Using a joystick, much like operating a helicopter underwater, the pilot could manoeuvre the ROV and grasp the crumbling containers, readying them for the crane. The smaller arm plucked debris from the ocean floor.
Once the container is loaded into a cage, the crane operator hauls the load to the surface, allowing the water to drain, then swings it on deck. Pride boasts a 250-tonne active heave-compensating subsea crane and a 35-tonne auxiliary crane.
The ROV can work to depths of 300 m and uses subsea navigational aids, such as sonar, to locate missing containers on the seabed.
AMSA said it now intends to recover the costs of the operation; however, that is subject to court action.