DP II DSV Drift-Off Incident

U.S., Gulf of Mexico

On 3 April 2013, an offshore contractor, conducting saturation diving operations off of a DP II DSV, experienced a drift-off, while the bell divers were deployed from the bell.

The contractor was conducting 3-man Bell runs, at a depth of 360 FSW.  Two divers were deployed approximately 70’ from the bell. The sea state was calm, with light winds.

The divers were performing a series of large diameter spool installations, involving the use of an AHC crane.  The vessel went to an immediate red light once the taut wire sensor signaled out of limits.  Alarms were sounded.  Within two and a half minutes the vessel was stabilized, as the auto mode was reset.  The vessel drifted off location by approximately 100 feet (30 M), while still connected to a spool piece on the seabed.  The divers were recovered to the bell and the hatch was closed.  Once the vessel was back to its initial location, the ROV was launched to disconnect the crane from the spool piece.

The vessel was moved clear of the 500 M zone of the structure, until it received instructions to return to the dock for an investigation.

DPO willingly, unknowingly, or inadvertently pushed the button that switches station keeping from automatic to manual and set the vessel adrift.  This was verified and confirmed by the system’s Black Box.

Action Items that were completed prior to returning to work

• Relief of DPO
• Vessel specific training relevant to the incident; stress increased vigilance of DPO watch of remote possibility of undiscovered hardware or software malfunction.
• Vessel DPO specific training to decrease effective time to diagnose potential system faults and executing corrective action to stop the vessel movement.
• Install physical barrier over mode buttons (see DP Panel Photo)
• DPO watch to set up stand-alone watch circle alarms on the SETEX GPS units corresponding to the Clients Activity Specific Operating guidelines (ASOG) limits.

• Discussions with Kongsberg regarding if this DP panel has undergone a failure analysis that may prove or disprove potential circuitry fault which could have contributed to sending a command to the DP system without a deliberate push of the mode button.
• Kongsberg installing an audible alarm to the panel indicating a shift in DP mode.

Long term corrective action

• Identify a means through industry discussion to put into place system barriers to ensure that commands sent that shift the DP mode, increase the operator’s awareness of shifting modes.

All evidence points to human error on the part of the DPO.  

One important item to note; the DPO2-2012 K-Pos IO Bus Malfunction firmware version 2.7.0.15 had been installed on the vessel’s DP operators in December 2012, as an action item post the Bibby Topaz run-off.

The DP II DSV has been on charter for 46 months without any DP related incident.  Upon completion of the corrective actions, the vessel returned to work and had been incident free for almost two months.

The diving superintendent, diving supervisor, and dive crew were found to have responded to the incident admirably.  It was also noted that the client’s support of the diving contractor’s commitment to the performance of drills also mitigated any further negatives which could occurred with this incident.