Denmark’s investigation into the sinking of two Maersk offshore supply vessels in December 2016 showed that the incident emerged from a unique conjunction of events and circumstances.
The Danish ships Maersk Searcher and Maersk Shipper capsized on the night between December 21 and 22, 2016, and sank in the Bay of Biscay some 65 nautical miles off the French coast while being towed by another offshore supply ship, Maersk Battler, to Aliaga, Turkey.
The two vessels were configured in a side-by-side towing setup during the voyage. During the passage of the English Channel, the fenders between the ships on tow failed, and the ships started to interact. This caused damage to the ships’ superstructure, which eventually compromised Maersk Searcher’s watertight integrity and led to water ingress. Maersk Searcher capsized and sank, and subsequently Maersk Shipper was pulled under by Maersk Searcher. The crew on Maersk Battler carried out a controlled breakage of the towing wire and came loose of the foundered towage.
DMAIB informed that the foundering of Maersk Searcher and Maersk Shipper is regarded as a systemic accident. This means that local and technical circumstances unfolding on board Maersk Battler during the voyage cannot be isolated from the preceding organisational events and circumstances taking place months earlier. Thus, the investigation of the foundering is two-fold. It focuses on the technical circumstances leading to the foundering of the two ships and on the organisational circumstances facilitating these technical circumstances.
It is concluded that the loss of fenders, collision and flooding of the unmanned ships under tow had been addressed in the risk assessment carried out, and that risk mitigating initiatives were in place for each risk item.
“However, these initiatives were ineffective. The DMAIB concludes that the risk mitigating strategies were mainly focused on preventing risk factors in isolation and left little or no contingency for acute interaction between the risk factors.”