Untitled Quiz

Vessel Allision with Installation

• A PSV experienced a loss of DP position reference systems (PRS) during a cargo operation, resulting in contact with an offshore installation, causing minor vessel and installation damage.
• No injuries or environmental damage occurred.
• The vessel's DPS and PMS were operational for DP Class 2 operations.
• One PRS (CyScan) was unavailable.
• The vessel was operating under an amended Activity Specific Operating Guideline (ASOG) and an Operational Risk Assessment (ORA).
• Initial issue: Differential Global Navigation Satellite System (DGNSS) PRS signal instability.
• A RadaScan PRS responder was deployed as a backup.
• The master was not informed of the developing situation, violating ASOG.
• Both DGNSS and RadaScan signals were lost during approach to the installation.
• The DPS transitioned to Dead Reckoning (DR) mode, calculating a position 3.4m off and moving further, up to 8m deviation.
• The DPO intervened, taking control of the vessel's DPS in joystick mode.
• Vessel contacted a jacket leg on the installation due to momentum, swell direction, and reduced thrust allocation.
• Vessel exited the 500m zone to assess damage.

Cause Analysis

• DGNSS 1 and 2 position references were significantly degraded close to the installation due to platform elevation blocking signals.
• Differential corrections for both DGNSS systems were broadcast from the same satellite, impeding reliability.
• The RadaScan system failed due to an unknown software sensor error in multi-target mode.
• The DPOs did not recognise the increased risk of collision.
• The vessel had been operating without CyScan for 5 months due to long lead time for spare parts after a failure.
• The master wasn't informed of PRS degradation as per ASOG.

Key Learnings

• Importance of having multiple, independent position reference systems based on different principles.
• Critical to maintain awareness of any degraded PRS conditions in DP Class 3 situations. A change in positioning mode requires the vessel to return to the final set-up area and a final assessment before making any changes.
• Importance of timely reporting of PRS issues as per activity-specific guidelines.
• Proper training, familiarization, and competency assessment for DP personnel (especially handling DP failures).
• Drifting assessment procedures and adherence to guidelines during offshore work.
• The implications of relying on dead reckoning.