Learnings From Incidents (LFI) are published to promulgate learnings from incidents to enable industry to proactively manage root causes of known failures and so minimize potential for repeat DP loss of position incidents. It is recommended that owners of DP vessels disseminate LFIs to all their DP Vessel management teams, to their vendors of DP FMEAs and to their DP Technical Support Function. It is recommended that Vessel Management Teams and DP Technical Support Functions review this LFI and after a specific review provide positive confirmation to their organizations DP Technical/Quality Focal that their specific vessel designs and documentation were reviewed against this LFI and are not vulnerable to the identified or related root causes of the subject incident. Results of this investigation should be communicated back within a mutually agreed time. If vulnerabilities have been identified Vessel Management Teams and DP Technical Support Functions should communicate the initial remediation measures being undertaken along with timelines for full correction. Further information on the lessons learned or support to the business if required can be obtained by contacting the MTS DP Committee.
You may download the LFIs at no charge:
- 2015-1 - Blackout on a Segregated Power Plant
A DP 2 vessel carrying out light subsea inspection repair maintenance activities had a blackout and as a consequence had a loss of position (LOP) incident. The vessel was operating in open water and there were no consequences to people, assets or environment associated with this LOP incident. Designs with cross connections across redundant groups are vulnerable to larger failures with the potential to experience serious consequences.
Type of Incident: Power
Cause: Cross connections
DP Pillars: These illustrate the fundamentals of DP technical reliability, they are
• Independence
• Segregation
• Autonomy
• Fault resistance
• Fault ride through
• Differentiation
This incident demonstrates the failure to achieve Segregation. See the MTS DP Committee Design Guidance section 3.3 for more information - 2016-1 - External Interface with DP Station Keeping Equipment
A DP class 2 project and construction vessel suffered a position and heading excursion while conducting coiled tubing operations. The incident had no consequences to people, assets or environment. The following sequence of events was reported: • The DP system displayed a “heading out of limit” alarm and a “position out of limit” alarm.
• The vessel experienced a maximum heading deviation of 6 degree and position deviation of 4 meters.
• Bow tunnel thruster’s ramped up in response to the deviation noted on the DP system and a high force warning alarm was recorded.
• Vessel crew deselected DGNSS #1 from the DP system assuming that the excursion was caused by a DGNSS jump.
o Vessel’s crew reported that GPS “jumps” were observed on the radar an hour prior to the excursion event.
o No alarms were recorded on the DP system indicating issues with the DGNSS.
o Subsequent follow up and review of the logged data by the vendor of the DGNSS’s did not reveal any issues with the DGNSS PRS.
• Yellow limits were triggered by thruster load criteria and operations were suspended in accordance with the ASOG and vessel departed the 500 m zone.
- 2016-2- Complete Loss of Propulson on a DP Class 2 Vessel
On 28 May 2016, the platform supply vessel (PSV) sustained a complete loss of propulsion while operating near a platform at the Thebaud natural gas field off Sable Island, Nova Scotia. At the time, the vessel was preparing to inspect a natural gas pipeline using a remotely operated vehicle (ROV) and was maintaining a position near the platform while in dynamic positioning (DP) mode. The winds were westerly at approximately 10 to 12 knots, and the current was south-southeasterly at 0.16 knots. Subsequent to the loss of propulsion, the vessel’s stern made contact with one leg of the platform, and then the blow made contact with another leg of the platform.
While the vessel lost propulsion, a series of alarms sounded indicating that both man engines and all four thrusters had shut down. The engine room was notified immediately. The master took the vessel out of DP mode and attempted to manually control the vessel’s movement through the use of rudders, but this was ineffective without the main engines or thrusters. The No. 1 auxiliary generator remained running, preventing a complete blackout of the vessel. Following the occurrence, the No. 1. Main engine was restored and the vessel was maneuvered away from the platform and outside the 500 metre safety zone, where all propulsion systems were restored. There were no injuries or pollution as a result of the vessel’s contact with the platform. - 2017-1- DP Class 3 MODU exceeded WCF while operating with open busties during a heavy weather event
A DP Class 3 MODU carrying out drilling operations, and operating in a 3-split bus configuration, had a near simultaneous trip of 3 generators from two of the independent power systems during a heavy weather event. Each of the vessels redundant power systems had the two generators and two thrusters connected and operating correctly. Due to the simultaneous trip of two generators from one of the redundant systems the vessel suffered blackout on one of the switchboards.
The vessel had been pushed off station by a large wave, but had remained within the yellow watch circle, and was recovering position when the blackout occurred and then continued to return to and maintain station while the technical team restored the power system.
The vessel at no time required to be disconnected from the wellhead and had been operating in accordance with the Class approved shipyard DP FMEA and within the requirements of the WSOG. - 2017-2- Backup DP Transfer Switch Functionality
During a DP control transfer drill, the Emergency changeover switch from ‘Main’ DP to ‘Backup’ DP system, located in Engine Control Room (ECR), was observed to be out of alignment. The decision was made to make the switch correction when the vessel was not in DP, so as to have adequate risk controls in place. Later, in preparation for the task, the vessel was in Independent Joystick (IJS) mode. The DPO set up the DP backup system in standby mode as an additional barrier. When the changeover switch was turned from ‘Main DP to ‘Back up DP’ position, control of the propulsion was transferred from IJS to DP Backup. Why it happened
Control of Thrusters was transferred from IJS to DP backup system. All thrusters reduced the load to the demand setup in the Backup DP system (zero thrust). The DP system has a NetIO signal telling the Thruster controllers directly that the backup has taken command. The purpose of this is to bypass the bridge utility panels in case the bridge is no longer usable. Upon the reception of this signal, the Thruster system will force the command of each thruster to DP mode. The DP in turn, will be controlled by the backup DP system, since the transfer switch is in backup mode. In the VMS thruster module there is a configurable parameter called “Auto DP Mode”, this bit is normally set to 1 by the DP vendor during installation. When set to 1 and the Backup DP switch is selected, the thruster will transfer to the Backup DP regardless of the mode (i.e. DP, IJS, Lever, Auto pilot) selected. - 2017-3 - Addendum: Examples of Verification Activies for Fail Safe Condition of Thrusters
This document outlines an example verification process to address self-assurance activities for fail safe condition of thrusters. This may be used to document and make available the outcome of verification activities. - 2017-3 - Fail Safe of Thrusters
At the time of the failure, the vessel was taking stores from a small harbour boat and preparing to commence diving operations. The vessel was operating on DP and in accordance with the ASOG.
A significant loss of position event was experienced. (Position excursion of around 70 metres in approximately 74 seconds). The potential consequences triggered an incident investigation using the guidance and tools provided by the MTS Techop on DP Incident Investigation.
Please DO NOT contact the authors of these documents direct. If you have an incident you would like to share with the industry please send to info@dynamic-positioning.com .