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Loss of tow and subsequent foundering of two vessels

What happened

The Danish Maritime Accident Investigation Board (DMAIB) published a Marine accident report on Mærsk Battler’s loss of tow and the foundering of Mærsk Searcher and Mærsk Shipper in the Bay of Biscay on the night between 21 and 22December 2016. Mærsk Searcher and Mærsk Shipper were configured in a side-by-side towing setup. During the passage, the fenders between the vessels on tow failed, and the vessels started to interact. This caused damage to the superstructure, which eventually compromised the watertight integrity of Mærsk Searcher and led to water ingress. She capsized and sank, and subsequently Mærsk Shipper was pulled under also. The crew of the towing vessel Mærsk Battler carried out a controlled breakage of the towing wire and came loose of the foundered towage.

The DMAIB regards the foundering of the two vessels as

… a systemic accident. This means that local and technical circumstances unfolding on board Mærsk Battler during the voyage cannot be isolated from the preceding organisational events and circumstances taking place months earlier. Thus, the investigation of the foundering of Mærsk Searcher and Mærsk Shipper 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 in the report 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.

A full marine accident report has been prepared in English and is available at

Members may wish to refer to the following incidents:

Safety Event

Published: 15 November 2017
Download: IMCA SF 29/17

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