On 4 February 2025 a tug assisting a car carrier at Royal Portbury Dock, Bristol, suffered a towline failure. The tow rope parted under excessive load during an overcorrection in a ship-handling manoeuvre and recoiled into the wheelhouse. The forward and aft windows shattered, and the master and mate were injured by flying glass. The UK Marine Accident Investigation Branch (MAIB) published its report (2/2026) on 12 June 2026 (read the report).
A repeat failure
The MAIB notes that the same rope had parted before, in July 2024, after about 800 towing tasks. It was turned end-for-end and returned to service, and it parted again on its 307th task after that.
The MAIB found that the operator's towline risk management relied on visual inspection and rope rotation. It did not follow best practice or carry out residual strength testing on parted ropes. The report also raises supervision and training issues, and a normalisation of towline failures. The Chief Inspector urged the operator to reconsider its response to an earlier MAIB recommendation on minimising towline failures and protecting crews if a line parts.
Why visual inspection is not enough
Synthetic fibre ropes lose strength through internal abrasion, fatigue from repeated loading, heat, ultraviolet exposure and chemical contamination. Much of this damage is internal or spread along the length. A rope can look serviceable while its breaking strength has fallen a long way.
The same applies to webbing slings, fibre-reinforced composites, elastomeric components and many other load-bearing items.
Using failures and tests as evidence
Residual strength testing means taking retired or failed items and testing them to failure in a controlled way. Over time this gives you:
- a measured relationship between service life, condition and remaining strength;
- evidence-based retirement criteria (number of tasks, hours, or observable condition);
- early warning if a new supplier, product or duty changes the degradation rate.
Failure investigation of a parted rope, or of any failed component, answers a different question: was this an overload, a degraded item, or both? The answer decides whether the fix is operational, maintenance-related or a change of specification.
Questions to ask
- What evidence supports the retirement criteria for your ropes, slings and other consumable load-bearing items?
- When one fails, is it kept and examined, or discarded?
- Do you know the actual remaining strength of items at your current retirement point?
How MTIS can help
MTIS provides materials characterisation and testing and failure investigation. We can coordinate testing through partner laboratories and turn the results into practical inspection and retirement criteria. Contact MTIS to discuss a testing programme.
Source: UK Marine Accident Investigation Branch, report 2/2026, failure of a tow rope and injury to crew on board the tug Svitzer Avon, published 12 June 2026. Summarised in our own words.