On-board Diary: The ROV, entangled in a lost fishing net
Author: Xavier Pastor - Baltic Sea Expedition leader
Date: April 29, 2012
Last night our ROV was confronted with what is the worst enemy of the underwater robots: the lost fishing nets. While carrying a night operation, we detected an abandoned trawling net that was stuck on the sea bottom. While trying to avoid it, the ROV was caught in several of the ropes around the fishing gear. We started then a careful process of disentanglement maneuvering the robot propellers. But with no result. As the minutes were passing, the robot was hopelessly being paralyzed as in a spider web.
After one hour of efforts, the only option that seemed feasible was to dive to free the machine. Easy to say, but that operation represented a high risk operation for the divers. The ROV was entangled at 30 meters depth, with no visibility, with an extremely low water temperature, surrounded by nets that could be a dangerous trap for the divers. It was a dark night and there was a 1.5 knots current that could drag the divers away before they were detected and rescued by their colleagues onboard the Hanse Explorer and her inflatable boats. The low temperature did not allow for any mistakes, so the diving operation was planned with all kind of safety measures in mind.
At the end, those were not needed. Just before the divers jumped into the water, the ROV operator made a last attempt. He used all the power of the robot’s six small propellers and it shaked itself as a shark on a fishing net. Through its own cameras, we could see how the ROV was freeing itself, and how it started its way back to surface. There it was recovered and put onboard with some sights of relieve.
The machine has suffered some minor damages in its struggle against the fishing gear. We are repairing them, but they are not essential for its operation. In fact, it is already working in the water again.
In the Oceana ships we have a strict no-alcohol consumption policy. But last night, after having shared a lot agony, we decided to indulge in sharing some buzz.