Hi,
The Remora robot can work as far down as 6,000 meters. To ensure steady operation, a team of nine Phoenix experts will operate the 900-kilogram sub from the ship using large video monitors to track its progress. Every movement of the vessel at the surface is translated to the Remora's umbilical cable with a delay, said Brennan Phillips, manager of ROV operations at the University of Rhode Island in the U.S.
Delayed Reaction
"If the ship moves, it takes half an hour for the vehicle to feel it," he said. "You need an extremely stable ship."
I wonder why they don't use a compensating system (hydraulic-air) like used on the drill rigs (semi) or DS for the risers tensionners and on the derrick travelling block