Case study – Switching from auto DP to IJS (independent joy stick) mode caused loss of control

Case narrative

A vessel collided with the working platform on a wind turbine transition piece. The incident occurred during worsening weather conditions. The vessel was on auto DP, when it was decided to pull off. Whilst moving away from the turbine, the DP operator switched from auto DP to independent joy stick (IJS) mode. The thrusters’ set point went to zero for the deselected surge, sway and/or yaw axis the moment the change was made, leaving the vessel without axis control, approximately 120m from the turbine.

The wind was 28 knots. The action of the environmental forces started to drift the vessel back towards the turbine. The crew attempted to gain control of the vessel using the IJS. They were ultimately successful in regaining control of the vessel but were unable to prevent collision with the transition piece and its work platform.

Note: after the incident the vessels DP, IJS and manual thruster control systems were extensively tested. An additional FMEA test was carried out. All systems were found in good working condition without any technical defects found.

What went wrong

The following points were noted:

• Officer of the watch handover procedure was unclear to those involved
• The decision to change over in a position in close proximity to the transition piece was inconsiderate
• The master misjudged how the systems would perform during the transition from DP to independent control.

What were the causes

• Poor judgement of situation by the vessel master
• The vessel was already moving against an increasing wind and was still within the wind farm boundary
• Insufficient awareness of DP system handover procedures and the adverse effects in the actual situation.

Actions

• Revision of DP operations manual to fully cover changeover procedures
• Revision of DP familiarisation process to include better verification
• Introduction of recordable in field passage planning.

Lessons learned

• Full understanding on changeover procedures and relationship between (DP) systems
• Full understanding of vessels DP systems and verification thereof (no DP system is the same, despite naming)
• Bridge resource planning, especially transiting between work areas should be improved.

Considerations of the IMCA Marine DP Committee

IMCA seeks to raise awareness of the importance of detailed operational activity planning both in the offshore renewable energy sector and in the offshore oil and gas sector. Within an offshore wind farm there are many fixed assets which present a high risk to the navigator. It is considered that detailed planning and care is required to ensure safe operations. Guidance: IMCA M 220 – Guidance on operational activity planning.

Note that this case study has been issued within IMCA Safety Flash 15/18.