Web alert:The grounding of MODU Kullak, a reminder to ensure proper towage assessment.

The U.S. National Transportation Board (NTSB), in a 14-page report, have concluded that the probable cause of the grounding of the mobile offshore drilling unit Kulluk was Shell’s inadequate assessment of the risk for its planned tow of the Kulluk, resulting in an insufficient tow plan to mitigate the risks during the towage.

Background

The brief background is that on 31 December 2012 the MODU Kulluk was under tow by the AHTS Aiviq to Seattle for maintenance and repairs, to enable the MODU to be ready for the upcoming 2013 drilling season, offshore Alaska. The Kulluk had just completed a drilling season in the Beaufort Sea. The towage encountered heavy prevailing sea and wind conditions resulting in the loss of power and broken tow lines, eventually resulting in the grounding of the Kulluk near Ocean Bay on the eastern coast of Sitkalidak Island off Kodiak Island, Alaska.

Notwithstanding the grounding, the Kulluk maintained watertight integrity but suffered widespread damage to the superstructure, electrical equipment, lifesaving and safety equipment, and interior and engineering spaces. No environmental damage was found as a result of the grounding. The Kulluk was refloated and loaded on to a heavy lift and transportation vessel, and shipped to China where it was scrapped. It was determined that it was not cost-effective to repair the Kulluk.

NTSB report

The NTSB asserts that it was not a single error or mechanical failure that led to the accident but rather the shortcomings of the towage plan, which they say had an insufficient margin of safety for that time of year when there was a known likelihood of severe weather conditions. According to the report, the day after departure, the Aiviq master wrote an e-mail to the Kulluk tow master stating, in part, “I believe that this length of tow, at this time of year, in this location, with our current routing guarantees an ***kicking”.

The reports states that: “Given the risks associated with this transit, including the likelihood of the tow encountering severe weather, Shell and its contractors, particularly Offshore Service Vessels, the operator of the Aiviq, who reviewed and approved the tow plan should have either mitigated those risks or departed at a time of year when severe weather was less likely. For example, Shell and its contractors could have included additional tow vessels to the entire transit to reduce the likelihood of catastrophic results from a failure of the Aiviq or its tow gear. Redundancy is a necessary element of safety-critical transportation systems, and given the hazards of operations in Alaskan waters, those involved in the tow plan should have recognized and addressed the lack of redundancy. The series of failures that led to this accident began when Shell failed to fully address the risks associated with a late December tow in Alaskan waters, and ended with the grounding of the Kulluk.”

Conclusion

Although a number of parties were involved in the approval of the tow plan, it was Shell in this case who were to implement the tow. Accordingly, the NTSB state that they are to be considered responsible for the grounding. The lesson is possibly that whatever part a party may play in a towage, all should ensure that a proper towage assessment is in place. Of course if the master did have such concerns at the start of the voyage, why did he continue?

Category: Offshore & Renewables