Unreliable position reference systems leads to DP incident

Comments from the report

Only 2 DGNSS were online, with poor signal quality due to the location and environmental conditions.  The end effect was that the deviation from the set point in surge and sway were increasing for each oscillation.

Considerations of the IMCA Marine DP Committee from the above event

  • For DP2 operations, the use of only 2 DGNSS systems is insufficient; a minimum of 3 systems are to be used based on 2 principles.
  • The importance of monitoring the position reference systems (PRS) screen cannot be overstated; this then ensures that all the PRS agree on the position of the vessel.
  • It is evident that the selected PRS were not providing reliable position information and highlights the problems that can be experienced when at least one reliable PRS is not available.
  • It was noted that the move was paused at 2005; this should have provided the opportunity to investigate and correct the situation rather than continue with the move.
  • It is also worth considering that the erratic movement of the vessel could indicate that the DP system needs retuning.