CHENNAI: At 6 km depth, the pressure was over 500 times that on the surface while the ambient temperature was 3-4 degrees Celsius.
Such hostile oceanic conditions made the soft-soil seabed locomotion extremely complex, but the team from National Institute of Ocean Technology (NIOT) persisted and accomplished it with great precision.
Chief Scientist K Gopakumar told Express that the expedition started on March 20, meeting all the Covid protocols, on board the ship ORV Sagar Nidhi at Chennai Port.
The ship was an infection-free bubble; all the team members had to prove that they were neither infected nor carriers.
The ship had a dedicated crew to operate and maintain her. The project team were the designers, developers, and operators of the mining systems.
“Post statutory clearances, the ship sailed out on March 24 early morning. A few hours later, we did our check-dive in the Bay of Bengal at depths of 3,206 m. This was to test the mining system for its functionality at high depths, test the ship systems for integrated operations and to work up the trial team before proceeding to the trial site, lying on the southern latitudes of the Central Indian Ocean (CIO),” he said.
The distance from Chennai to the trial site at the CIO is about 1,700 nautical miles (approximately 3,000 km).
The team reached the site on April 4, about 11 days after its departure from Chennai.
The southern latitudes have rough weather and high swells for long periods of time. One has to wait patiently for a crack of fair weather to carry out such extensive deep-sea missions.
The team even had to move little northward (within the allocated mining area) in search for improved ocean-state conditions.
Moment of truth
Finally, on April 16, the trial commenced at 1115 hour (11.15 am).
The mining system was lifted off the deck using a custom-built umbilical cable, the deep-sea winch, and ship’s stern (back) mounted A-frame and lowered into the water.
It took the machine over four hours to reach 5,000 m depth. Tense, the team on board the ship monitored and recorded every aspect and parameter.
The systems were periodically switched on and tested during the descent to ensure that they worked and maintained integrity. The crawler touched the seabed 5,270 m underwater by 1538 hour (3.38 pm).
120m in 2 hours
The robotic system was driven remotely from the ship using the 6500-m-long umbilical-cable connection.
The seabed locomotion continued at various speeds within planned mining speed-range; a distance of over 120 m was covered in 2 hours.
All the systems worked as expected and all related data were collected according to our trial targets, the team told Express.
Lift off from the seabed was smooth. By 2110 hour (9.10 pm), the system was on the deck. A few more tests of the systems were conducted at the site before starting the return journey to Chennai.
Tense moments
Operations at sea, especially at over 5000 m depth, are always complex, especially when the weather is so fickle.
Besides, such deployments and trials require a large number of specialised equipment, controlled remotely and staffed and managed by a large team of engineers and marine crew working in tandem, the team said.
How they pulled it off
The team, comprising researchers and engineers, has been working on the project for over a decade.
Development efforts on the specific mining system have been going on for the past three years.
Several sea tests were undertaken, progressively increasing depths; the problems encountered were addressed and systems re-designed.