Routine maintenance leads to loss of thruster
- DP Event
- Published on 29 May 2018
- Generated on 6 January 2026
- DPE 02/18
- 2 minute read
Undesired event
When obtaining an oil sample, the valve was opened fully, reducing the pressure to the pressure switch.
Comments
During a routine weekly maintenance operation, a ships engineer took an oil sample from the starboard azimuth thruster sample point, which is a small valve located on the line to the pressure switch.
The location of the oil sample point on the line to the pressure switch creates a risk of inadvertently activating the switch if the sample valve is opened too much. When obtaining the sample, the valve was opened fully, reducing the pressure to the pressure switch.
The pressure switch then tripped causing the thruster to stop; the oil pressure in the thruster was maintained and not at risk. Once the sample valve was closed the pressure on the line to the pressure switch returned to normal.
The starboard azimuth was started back up in DP and, following a short investigation, pre-dive checks were carried out and the bell deployed to continue diving operations.
Considerations
- The loss of redundancy should have initiated a yellow alert but this was not in the report.
- Planned maintenance of critical equipment should be controlled by a permit to work (PTW) system.
- It appears that during the event, co-operation between the bridge, engine room and diving departments was good.
- The event highlights a poor design, for example the sample point could have been down stream of the oil pressure sensor and in this situation, it would seem reasonable for an alarm to be triggered rather than the thruster shut down.
Latest DP incidents
-
Simultaneous Operations
A DP Incident report highlighting the importance of maintaining focus during time on the DP desk
DPE 03/25
18 December 2025
Incident
-
Importance of familiarisation and paying attention
The importance of maintaining full attention during the operator's time on the DP desk can never be underestimated, or forgotten
DPE 03/25
18 December 2025
Incident
-
Worst case failure preparedness
Operators must be prepared for worst case failures
DPE 03/25
18 December 2025
Incident
-
Know your settings
This Dynamic Positioning (DP) incident involved a DP equipment class 2 offshore supply vessel (OSV) during loadout operations from a drilling rig.
DPE 03/25
18 December 2025
Incident
-
DP drill scenario
DP emergency drill scenarios are included to assist DP vessel management and DPOs / Engineers and ETOs to conduct DP drills onboard.
DPE 03/25
18 December 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.