A report has been issued about an incident that saw a vessel collide with an offshore wind turbine.
The report from the International Marine Contractors Association (IMCA) said the vessel collided with a working platform on a wind turbine transition piece.
The incident occurred during worsening weather conditions. The vessel was in dynamic positioning (DP) mode when it was decided to pull off. While moving away from the tower, a switch was made from DP to independent joystick control.
Once the switch was made, the thrusters returned to zero pitch, effectively leaving the vessel without drive, approximately 120 m from the transition piece.
The wind was 28 knots. The action of the weather and sea had already started to turn the vessel back towards the transition piece.
The crew attempted to regain control of the vessel using the joystick. They were ultimately successful in regaining control of the vessel but were unable to prevent two collisions: one between the transition piece external working platform and the upper bulkhead of the vessel, and a second between the vessel’s crane platform and the work platform.
After the incident, the vessel’s DP systems, joystick systems and manual control systems were extensively tested. An additional failure modes and effects analysis (FMEA) test was carried out. All systems were found in good working order without any technical defects.
IMCA said an investigation that took place after the incident found that the procedure used for the handover to the new officer of the watch was unclear to those involved. The decision to change over in a position in close proximity to the transition piece was ill-considered. The master of the vessel misjudged how the systems would perform during the transition from DP to independent control.
Addressing the causes of the incident, the report noted poor judgement of the situation by the vessel’s master; the fact that the vessel was already moving against an increasing wind and was still within the windfarm’s boundary; and insufficient awareness of DP system handover procedures and the adverse effects in the actual situation.
Actions taken subsequent to the incident included a revision of the DP operations manual to fully cover changeover procedures; revision of DP familiarisation process to include better verification; and the introduction of a recordable infield passage planning process.
Among the lessons learned highlighted by IMCA were the following:
A full understanding of changeover procedures and the relationship with DP systems is essential.
A full understanding of vessels’ DP systems and verification is essential, as is the fact that no DP system is the same as any other.
Bridge resource planning – especially transiting between work areas – should be improved.
IMCA said it seeks to raise awareness of the importance of detailed operational activity planning, both in the offshore renewables sector and in the offshore oil and gas sector.
In an offshore windfarm there are a large number of fixed assets that present a high risk to the navigator. These risks should be considered and detailed planning and care is required to ensure safe operations.
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