On 22 December 2019, the Port of Southampton tug Svitzer Mercurius was assisting with the berthing of an ultra-large container ship. Svitzer Mercurius, acting as the stern tug, was requested to give 100% astern thrust to slow the container ship using its starboard towline on the forward towing winches. The brake of the tow winch slipped briefly, subjecting the towline and towing pennant to a sudden shock load as the brake regained grip. The pennant suddenly parted, causing it and the towline to recoil back toward the tug. The towline hit and shattered the tug’s starboard forward wheelhouse window, resulting in glass particles injuring the five crew inside.

Safety Issues
• Svitzer Mercurius had been recently acquired and its temporary crew had not been inducted sufficiently before starting towing duties
• the towline pennant broke at about 52% of its original minimum breaking load and was not fit for purpose
• the wheelhouse windows were designed to withstand water pressure and not intended to withstand impact from a towline

Safety recommendations
The tug’s classification society has been recommended (137/2022) to take the findings of this investigation to the International Association of Classification Societies to develop a unified requirement to minimise, in the event of impact from a recoiling towline, the risk of injury from broken window glass to personnel within tug wheelhouses.
A recommendation (138/2022) has also been made to the tug operator to review the risk to wheelhouse crews across its fleet posed by towline snapback and, where it is assessed to be high, evaluate the viability of introducing laminated glass for wheelhouse windows

Source: MAIB