Tug Biter Capsizes and Sinks — Two Fatalities During Passenger Vessel Escort

Girting: A Capsize With No Recovery

At approximately 1527 on 24 February 2023, the conventional twin-screw tug Biter capsized and sank off Greenock while attached to the stern of the passenger vessel Hebridean Princess. Hebridean Princess accelerated unexpectedly to around 5 knots. At that speed, with Biter's tow line configuration, the line was pulled to a side-on angle — girting the tug. Once a conventional tug girts, the heeling force from the tow line exceeds its righting moment and capsize cannot be reversed by any propulsion input. It happens in seconds. Both of Biter's crew died.

A Gob Rope Attached to the Wrong Post

A gob rope restrains the tow line's angle, keeping it within a safe arc astern of the tug. Biter's was inadequately specified for the forces involved, and was secured to the port samson post rather than a more central, robust structural attachment — reducing its effectiveness at the exact moment it was needed. Biter's watertight integrity was also compromised, which accelerated the flooding once she went over.

The Exchange That Didn't Cover Speed

The investigation found the pilot/tug exchange (PTX) beforehand — the primary mechanism by which a pilot communicates intended manoeuvre, speed profile and tug positions to tug masters — was inadequate. Biter's tug master wasn't given a clear maximum safe speed for his configuration, and had no explicit, agreed protocol for calling a halt if the ship moved faster than his tug could safely handle. When Hebridean Princess accelerated, nobody on her bridge had a shared model of what that speed meant for the tug astern.

No AIS, and a Question About Fitness

Biter carried no AIS — not required for harbour tugs at the time — meaning no automatic electronic record existed of her position and speed through the accident sequence. The investigation also questioned whether the tug master's medical fitness had been appropriately assessed for the demands of high-risk tug handling in pilotage waters, finding the assessment processes for harbour tug masters lacked clear, consistently-applied standards.

Recommended Actions

The findings from MAIB Report 17/2024 point every port operator running conventional tug escorts toward the same practical actions:

1. Inspect the gob rope on every conventional tug: confirm it is specified for the maximum expected towing load and attached to the correct structural point, not a marginal fitting
2. Before every escort or towing operation, brief the maximum safe ship speed for the tug's configuration to the bridge team and pilot, with an explicit protocol for the tug master to call "stop" or "reduce speed" at any time
3. Ensure the pilot/tug exchange covers intended manoeuvre, planned speed profile, tug attachment points, and any non-standard aspects — with tug masters confirming receipt and understanding before the operation starts
4. Confirm all watertight closures on a tug are secured before any towing operation begins
5. Consider fitting AIS to harbour tugs and workboats as best practice, for both situational awareness and investigation value
6. Establish clear, consistently-applied medical fitness standards for harbour tug masters, appropriate to the demands of the role