WATCHOUT - DP system failure on diving support vessel leads to serious incident

In this series, we take a look at maritime accident reports and the lessons that can be learned

What happened?
Two divers working from a dive support vessel were carrying out valve operations for barrier testing. While they were underwater, the vessel’s DP system suffered a malfunction. This caused its alarms to activate, quickly followed by a loss of all analogue and digital signals. The vessel started to drift away from its position. The divers were pulled along with it and instructed to return to the bell staging immediately. While the first diver was able to return to the dive support vessel safely, his colleague was not so fortunate. His umbilical line caught on a transponder bucket on the face of the drilling template, cutting off his main oxygen supply and severing communications. The Master steered the vessel manually to move as close as possible to the stranded diver, who was by now unconscious on the seabed. The diver who had made it back to safety returned to the water and rescued his colleague. Both divers were put in decompression chambers onboard the vessel and went on to make full recoveries.

Why did it happen?

• The DP system failed due to a number of technical faults, which caused a loss of communications between the control computer and its positioning references and environmental signals. The system’s thruster command signals moved to zero thrust and the ‘gyro ready’ signals failed, leading to heading and position dropout and the vessel drifting off position.
• The movement of the ship dragged the divers away from where they were working underwater. As they were pulled along by the drifting vessel, the umbilical line of the second diver snagged and he became disconnected from his main oxygen supply.
• The diver also lost communications with the dive support vessel during the incident, meaning that the diving support vessel’s Master had to use his locator beacon and steer manually to find and rescue him from the seabed.
• The Master’s training and skill made it possible to keep the vessel in position while the rescue was carried out.

What changes have been made?

• Investigations and discussions were launched immediately after the incident, including a number of engagement sessions with key stakeholders.
• A project looking at improvements to diving and marine operations was also established, including examination of various aspects of bell staging, diving equipment and DP control systems.
• An educational film was made to highlight the issues arising from the incident and champion the bravery of those involved in the rescue.

AS THEY WERE PULLED ALONG BY THE DRIFTING VESSEL, THE UMBILICAL LINE OF THE SECOND DIVER SNAGGED AND HE BECAME DISCONNECTED FROM HIS MAIN OXYGEN SUPPLY

Read the full report

The Nautical Institute’s Mariners’ Alerting and Reporting Scheme (MARS) - https://www.nautinst.org/resource-library/mars.html - comprises a fully searchable database of incident reports and lessons, updated every month. If you have witnessed an accident or seen a problem, email Captain Paul Drouin at mars@nautinst.org and help others learn from your experience. All reports are confidential – we will never identify you or your ship.