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

🕑 5 min read words Safety • Incident

Vessel: Biter — conventional twin-screw harbour tug, operated by Clyde Marine Services, escorting passenger vessel Hebridean Princess
Date & location: 24 February 2023, approximately 1527, off Greenock, Scotland
Outcome: Biter girted, capsized and sank. Both crew members — the tug master and one deckhand — died
Human factors: Situational Awareness · Authority Gradient
Source: MAIB Report 17/2024 (full investigation; an earlier Safety Bulletin covered the same accident in 2023)

6 decision points2 outcome paths — challenge the speed / ride it out~8 min read + Knowledge Checker

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:

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
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
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
Confirm all watertight closures on a tug are secured before any towing operation begins
Consider fitting AIS to harbour tugs and workboats as best practice, for both situational awareness and investigation value
Establish clear, consistently-applied medical fitness standards for harbour tug masters, appropriate to the demands of the role

Human Element Analysis

Situational Awareness

Neither the bridge team on Hebridean Princess nor the pilot had a shared model of Biter's vulnerability at speed. The pilot/tug exchange hadn't established a clear speed limit or a real-time communication protocol — so when the ship accelerated, nobody on the bridge had the information that would have triggered a speed check.

Authority Gradient

In port tug operations, the pilot directs and the tug masters are expected to execute. Without a pilot/tug exchange that explicitly establishes mutual understanding of speed risk, and a clear mechanism for tug masters to challenge a speed decision, that authority gradient operates silently — and it operated silently here, right up to the moment nothing could be done about it.

How This Pattern Repeats

Industry	Incident	The parallel
Offshore	Ocean Ranger semi-submersible capsize, 1982	A ballast control misunderstanding during a storm led to a capsize the crew didn't recognise as unrecoverable until it was too late — all 84 aboard died. The same 'point of no return, and nobody realised they'd crossed it' pattern as a conventional tug's girting threshold.
Aviation	Kegworth air disaster (British Midland Flight 92), 1989	The flight crew acted on an incomplete understanding of which engine had failed, and information available elsewhere on the aircraft that could have corrected it wasn't effectively challenged or passed up in time — the same authority-gradient gap that left Biter's tug master without a clear channel to challenge the ship's speed.
Nuclear	Chernobyl, 1986	Operators crossed a safety threshold during a test without recognising, in the moment, that the reactor had passed the point where the outcome could still be controlled — a parallel to a capsize mechanism that, once triggered, cannot be reversed by any subsequent action.

See How You'd Handle It

The scenario opens with the tow line starting to draw side-on as the ship ahead of you picks up speed. Do you call it immediately, or wait to see if it steadies? Six decision points follow, ending at the point conventional tugs can't come back from.

What Every Tug Master and Pilot Should Take From This

Tug girting cannot be recovered once it begins — prevention through speed control and tow line angle management is the only real defence
A gob rope has to be rated for the actual towing load and attached to the correct structural point — an inadequate one provides no protection at all
The pilot/tug exchange must set an explicit maximum safe speed and a clear, pre-agreed protocol for the tug master to call for a reduction — authority gradient kills when it operates silently
Watertight integrity on a harbour tug is safety-critical: a heeled or capsized tug floods faster with open closures
AIS on harbour tugs is a modest cost for a real gain in port situational awareness and investigation value

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