Over-Correction Led to Failure of Tow Rope

The UK Marine Accident Investigation Branch (MAIB) has published an assessment of the February 2025 tow rope incident onboard the tug Svitzer Avon.

At approximately 1954 on 4 February 2025, the UK registered tugs Svitzer Avon and Svitzer Brunel left the lock at Royal Portbury Dock, Bristol, England to meet the car carrier Auto Eco in the King Road approaches to the lock. Auto Eco had a pilot embarked for the entry into port and was to employ both tugs for a ship assist move into the lock and onwards to a berth in the dock.

Following an agreement made before departure Svitzer Avon’s relief master was supervising the mate, who was at the vessel’s controls for the move. The relief master was type qualified for the tug but had little experience on Svitzer Avon.

At 2003, the tug was in position astern of the car carrier. Svitzer Avon’s crew passed the towline, consisting of a tow rope and pennant joined with a cow hitch via a heaving line and messenger rope, to Auto Eco’s mooring deck where it was then made fast to a bollard. Having passed through the tug’s forward staple, the tow rope was held by the tug’s winch brake. Although fitted, a render system was not used.

At 2009, the pilot called Svitzer Brunel and requested the tug to standby on the port bow, followed shortly afterwards by the instruction “25% straight back” to Svitzer Avon.

At around 2011, an over-correction in handling occurred as Auto Eco was turning to line up for an approach to the lock and Svitzer Avon was maneuvering to hold position astern, causing Svitzer Avon to shear and heel. The tow rope parted under the increased load experienced during the recovery maneuver.

The tow rope recoiled, struck Svitzer Avon’s wheelhouse and shattered the forward windscreen glazing. Debris also caused the stern window to shatter. Flying glass caused minor injuries to the tug’s master and mate.

After checking each other for serious injury, Svitzer Avon’s crew quickly changed tasking with the bow tug to complete the move. Once Auto Eco was secured at the berth, Svitzer Avon returned alongside and was met by the port’s medical team. The master and mate were transferred to hospital, treated for their minor injuries and later discharged.

Findings

The relief master was not authorized to supervise the mate during the move.

The towage company’s training regime was not clearly defined or closely monitored.

The tow rope had previously parted in July 2024 after 800 tasks and had been changed end-to-end. The tow rope subsequently parted on its 307th task due to the excessive towline assembly loading experienced during an over-correction in a shiphandling maneuver.

The towage company relied on visual inspection and tow rope rotation for towline risk management. The company did not follow best practice nor conduct residual strength testing on parted ropes or as part of its towline risk management system.

The wheelhouse glazing met the appropriate standard.

MAIB investigated a similar accident involving Svitzer Mercurius in 2019 (MAIB report 15/2022), resulting in a recommendation 2022/138 to Svitzer Marine Limited to:

Undertake a fleetwide risk assessment to determine the level of risk associated with towline failure and snapback and the potential for impact by a line recoiling into wheelhouse windows, and, where appropriate, employ appropriate laminated glass or other defenses to mitigate against the risk of flying glass injuring its tug crews.

Actions taken

Svitzer Marine Limited has:

• formalized the designations of training masters and introduced a ‘trainers pathway’ and ‘training groups’ to standardize training practices across UK regions

• introduced a type rating framework of formalized training requirements for different vessel classes

• reviewed rope parting incidents and assessed impacts across the business

• ensured rope selection and usage aligns with operational risk.