Consequences of not following ASOG
- DP Event
- Published on 11 August 2022
- Generated on 23 June 2025
- DPE 02/22
- 3 minute read
Incident
A sudden rejection of the vessel’s starboard azimuth thruster by the vessel’s DP system without any warning... it started to drift astern.
Overview
An SOV was approaching a Platform for personnel transfer via use of onboard Personnel Access Platform (PAP) and the platform’s gangway. When the distance was approximately one metre between the gangway and the PAP, there was a sudden rejection of the vessel’s starboard azimuth thruster by the vessel’s DP system without any warning. The ‘ready’ signal was lost to DP Control for the starboard Azimuth thruster. The vessel started to drift astern.
After a few seconds, the starboard azimuth thruster readiness indicator on the Vessel’s DP Console showed ‘ready’. The DPO on duty immediately re-selected the thruster back into operation. After the re-selection of the previously failed thruster, the vessel continued to drift astern with the stern starting to rotate slowly to starboard. As the PAP was very near to the gangway, it made contact with the gangway and incurred damage. During the drift, the gangway also snagged against the ship’s structure at the ship’s stern.
The DPO immediately tried to move the vessel away using the DP joystick but found response was slow. The Master, who was at the manual thruster console at that time, immediately instructed the OOW to switch the vessel to manual control. He then took over command using manual control and manoeuvred the vessel away to avoid further collision with the platform. During the manoeuvre, the gangway which was snagged with vessel’s stern structure was dragged. It subsequently came dethatched from its securing point on the platform and finally remained suspended off the platform by its rigging.
There was no injury to personnel reported.
What happened?
While the vessel was manoeuvring into position to prepare for passenger transfer, the DP system reported an intermittent failure of one of two aft azimuth thrusters causing the starboard thruster to be incapacitated and de-select from DP Control, however the DP system still showed the thruster as ready, the operator re-selected the thruster back into DP Control.
The vessels DP system calculation was distorted by the inclusion of an unresponsive thruster and therefore could not stabilise.
The vessel could not hold position with the remaining Bow and Port azimuth thrusters.
What can be concluded?
- The vessel operating outside its post WCF environmental conditions prior to the loss of the thruster.
- The vessel was in a drift on position therefore situational awareness and possibly activity planning was inadequate given the environmental conditions being such that the vessel could not hold position with loss of one thruster.
- The ASOG was not followed as it stated that if the vessel status changes, then the re-selection of failed equipment is to be carried out only when it is in a safe position. The DPO shouldn’t have reselected the thruster back into DP whilst alongside the platform. DP operations should have been safely stopped and vessel moved to safe location before the DP system was recovered.
- The DP event report did not conclude why the DP joystick response was slow.
Latest DP incidents
-
Complete the job
Whilst connected to a turbine, an alarm was generated on the DP operator station, ‘Unbalanced load on SWBD 1’.
DPE 01/25
16 January 2025
Undesired event
-
How is your alignment?
Loss of the CyScan position reference system generated a reference system failure alarm and moments later the vessel began to lose position with the accompanying alarms.
DPE 01/25
16 January 2025
Incident
-
Beware your centre of rotation
The stern thrusters started to oscillate which transferred to an oscillating motion of the vessel and high forces were being used to try to maintain position.
DPE 01/25
16 January 2025
Incident
-
A-Tension
Whilst pipelaying in shallow water, the vessel experienced a tension sensor failure on one tensioner.
DPE 01/25
16 January 2025
-
DP Drill Scenario
DP emergency drill scenarios are included to assist DP vessel management, DPOs / Engineers, and ETOs in conducting DP drills onboard.
DPE 01/25
16 January 2025
Drill Scenario
The case studies and observations above have been compiled from information received by IMCA. All vessel, client, and operational data has been removed from the narrative to ensure anonymity. Case studies are not intended as guidance on the safe conduct of operations, but rather to assist vessel managers, DP operators, and technical crew.
IMCA makes every effort to ensure both the accuracy and reliability of the information, but it is not liable for any guidance and/or recommendation and/or statement herein contained.
Any queries should be directed to DP team at IMCA. Share your DP incidents with IMCA online. Sign-up to receive DP event bulletins straight to your email.