Installing and maintaining underwater cables has long been considered a high-risk operation, but with the development of remotely operated vehicles, safety conditions for engineers have been dramatically improved.
Across the bottom of the ocean floor, thousands of subsea cables are in place to transmit data, electricity and communications. This includes both fibre-optic cables for internet and communication, and power cables for offshore energy transmission, including from wind farms.
With more than 400,000 km of subsea cables connecting Australia to global telecommunications networks, there is a significant demand for reliable infrastructure to keep the lights on and the communications channels open.
Yet, installing and maintaining these cables has long been considered a high-risk operation, as, traditionally, human divers were required to descend to dangerous depths for repairs, facing extreme underwater pressure, unpredictable weather and other hazardous conditions.
The adoption of remotely operated vehicles (ROVs) in subsea operations in recent years has significantly increased safety conditions. As a result, the incidence of accidents and fatalities involving human divers has declined.
Reports from the International Marine Contractors Association have documented trends showing fewer fatalities and serious injuries. For example, the lost time injury frequency rate dropped between 2006-2020 from 1 per 100 million hours worked to 0.38 and the fatal accident rate dropped from 2.72 to 0.31 in the same period.
Remote operations at work
ROVs are equipped with cameras, sensors and robotic arms, allowing them to identify cable faults, perform burial or exposure tasks and even assist in splicing cables, according to Professor Stefan Williams, from the University of Sydney’s Faculty of Engineering and the Australian Centre for Field Robotics.
“Historically, cable-laying operations would have relied on manual processes to get the cables off the ship, and when you are operating in big seas it can be challenging to be on the deck,” he told create.
“Then, once the cable is down in deep water it’s very difficult to do inspections. You can’t dive to those depths, so repairs were done by using a grapple or similar to pull a cable up, repair it and then replace it.”
ROVs have changed that and the technology has brought major benefits to the safety levels of these kinds of operations, Williams said.
“People see this technology as a positive because it allows you to operate in much deeper waters in difficult conditions. It removes some of the hazards associated with more manual operations.”
Continual progress
For Italian cable maker and installation services provider Prysmian, who recently signed a $647 million contract to supply and install a new undersea interconnector between Victoria and Tasmania, the use of ROVs in their operations has increased safety and efficiency.
“Successful marine installation operations begin long before the cables are laid on the seabed,” a Prysmian spokesperson told create. “Engineering desks, IT simulators, control rooms, and skilled personnel on the laying vessels are essential components for ensuring a safe and efficient submarine cable installation.
“The use of ROVs for the continuous monitoring of laying and burial operations has also increased the level of control we can keep on our assets, and has therefore reduced the risk for damaging the cables or the surrounding environment.
“Cable-pulling, trenching, landings, are all done by machines and that has definitely increased the safety level of human operators.”
In a study reported in the Marine Technology Society Journal, automating the cable-laying system for the Dense Oceanfloor Network system for Earthquakes and Tsunamis (DONET) showed an increase in speed in positioning cables of approximately 0.1 kn from 0.5 kn, and the number of operators was reduced by half.
As the technology advances to allow fully remote operations that is likely to be even further reduced, Williams said.
“There are two main improvements that are coming,” he said. “One is using an uncrewed vessel that might launch an ROV to do an inspection or light intervention work that is directed by a satellite from shore, which further reduces the number of people who are out in these offshore environments.”
Some companies are already onboard with fully remote operations, including environmental consultancy Furgo, who also work with offshore oil and gas companies, he said.
“The surface vessel is uncrewed and deploys an ROV, while the people driving the system are actually in Perth or somewhere onshore.”
There has also been a lot of talk about autonomous intervention vehicles which, unlike traditional ROVs, are untethered and capable of navigating and performing tasks underwater on their own, Williams said.
“This technology is especially useful in remote or difficult-to-access areas, making interventions faster and reducing reliance on surface vessels but they must be built robustly to endure harsh underwater conditions, including strong currents. These vehicles must also operate with a higher degree of autonomy given that they aren’t directly connected to operators on the surface.”
In addition to the safety of humans, the environment is benefitting from ROVs, Williams said.
“ROVs are allowing operators to do fairly extensive surveys to understand the areas in which the cables are laid and to monitor operations directly while underway,” he said. “They can then route around a sensitive environment if they have the information to support that, whereas historically we just didn’t know what was there and it may have been laid straight through whatever might be on the seafloor.”