DP run-off incident – Class 2 DP vessel
- Safety Flash
- Published on 12 December 2006
- Generated on 18 April 2026
- IMCA SF 14/06
- 3 minute read
IMCA has received a report of a DP run-off caused by operational changes to the DP system which led to the loss of all reference systems.
What happened?
The DP class 2 vessel was alongside a platform and suffered a loss of reference systems, requiring the vessel to be taken into manual control. The vessel was recovered to a safe location without mishap. No damage was incurred to the platform or the vessel.
An initiating cause was the deterioration of the performance of one of the position reference systems. The DP operator on watch selected alternative reference systems to maintain DP positional integrity, in accordance with normal accepted procedures, whilst the problems with the deteriorating reference system were addressed.
The configuration of the vessel linked the faulty reference system with a number of other reference systems, with the result that the loss of one system caused the loss of others, including a vertical reference system (VRS).
The voting algorithm in the DP system was based on three VRS units, rather than two VRS units, as actually installed onboard the vessel. This caused the second VRS to be rejected by the DP system, with the secondary effect that all other reference systems were also rejected.
In addition, sensor offsets to the centre of gravity had been omitted, which caused erroneous calculations of movement, and errors in wiring compensating the pitch had occurred either at commissioning of the vessel or during maintenance of the DP system. This caused pitch motions to be amplified rather than compensated. There was insufficient documentation of these wiring changes onboard the vessel.
It should be noted that the errors could normally have been picked up during commissioning or annual FMEA DP trials, provided that the FMEA trial was not carried out in calm water, where the corrections for the vessel’s movements would have been too small to be distinguished. However, since FMEA trials test function and not configuration, the potential for error could remain undetected in the system.
Further, it should be noted that records of all system configurations, offsets, drawings, changes etc should be held onboard the vessel, and kept up to date.
The following actions were proposed:
- DP reference inputs should be correctly selected to mitigate loss.
- DP system configuration should be checked, as every vessel is different.
- All DP issues should be documented, together with the close-out issues, to aid the DP maintenance engineers as required.
- Configuration of individual reference systems should be modified such that VRS units cannot be inadvertently affected through failure of those systems.
IMCA Safety Flashes summarise key safety matters and incidents, allowing lessons to be more easily learnt for the benefit of the entire offshore industry.
The effectiveness of the IMCA Safety Flash system depends on the industry sharing information and so avoiding repeat incidents. Incidents are classified according to IOGP's Life Saving Rules.
All information is anonymised or sanitised, as appropriate, and warnings for graphic content included where possible.
IMCA makes every effort to ensure both the accuracy and reliability of the information shared, but is not be liable for any guidance and/or recommendation and/or statement herein contained.
The information contained in this document does not fulfil or replace any individual's or Member's legal, regulatory or other duties or obligations in respect of their operations. Individuals and Members remain solely responsible for the safe, lawful and proper conduct of their operations.
Share your safety incidents with IMCA online. Sign-up to receive Safety Flashes straight to your email.