It was a single rip tide and when it had passed the vessel was set up back in automatic position mode. There was clear evidence that a degraded performance was caused by the rip tide. A risk assessment was made, all DP set-up checks were carried out and the DP system performance was monitored for 20 minutes. Other rip tides were not observed and the vessel approached the installation to resume operations.
Considerations from the above event:
- The observation demonstrates a positive attitude to observing environmental conditions with respect to vessel capability and taking the correct actions to avoid potential dangerous loss of position.
- It is unreasonable to expect any DP system to cope with the sudden change in forces that can be introduced by rip tides which can have a catastrophic effect on the ability of a DP system to maintain position and heading.
- If this was a DP equipment class 2 operation then the report indicates that there was inadequate redundancy with regards to position reference systems.