Line parting as a result of socket failure during grapnel operations

A member has reported an incident in which a line parted during grapnel operations. The incident occurred as grapnels were being recovered during attempts to snag, capture and recover a cable on the seabed.

The end of the rope pulled out of its socket, releasing the rope down the aft deck and overboard. A bar at the stern was damaged and a camera and floodlight were carried overboard.

Our member noted the following:

• Higher than expected tensions were experienced during the recovery. At the time of the incident rope tension was observed to be 175kN;
• During watch handover, the situation regarding high tensions (averaging 130-140kN) was properly explained;
• The aft deck and “Snap Back Zones” were kept clear as per normal practice;
• The “Atlantic bar” was in place on the stern sheave;
• All ropes had been inspected (as per toolbox talks conducted and recorded) during pay-out and recovery, and there was no sign of excessive degradation to the failed rope or fitting prior to the incident;
• The recovery of the grapnels at higher than expected tensions, handover and safety briefing in unusual operation conditions, and back deck/snap-back zone safety were all handled diligently and professionally;
• The rope failed at less than the minimum breaking load (MBL) of the rope, which was 25.0 tonnes:
  • tensions of up to 200kN (app. 20 tonnes) had been experienced during the recovery
  • the working load limit (WLL) of the rope would have been 12.5 tonnes (app. 125kN) which was adequate for the expected tensions (app. 100-120kN / 10-12 tonnes);
• It is possible that the rope socket had gradually degraded over the previous 10 grapnel drives, but with no obvious visual signs of having done so.

Members may wish to refer to the following incident:

Loss of ROV after umbilical termination failure and damage to ROV during recovery