Eight Capsizes, Nine Deaths: What Tug Biter and Hebridean Princess Tell the Industry About Girting

Off Greenock, 24 February 2023

The tug Biter was assisting the passenger vessel Hebridean Princess off Greenock in the Clyde estuary when the towline angle increased beyond the tug’s safe working envelope. The towline generated a heeling moment the tug could not counter. Biter capsized and sank. Two crew members were killed.

The Marine Accident Investigation Branch investigated and published its report — MAIB 17/2024 — in November 2024. In February 2026, the MAIB issued Safety Bulletin SB1/2026: a safety video distilling the key lessons from the investigation for promulgation to tug crews across the UK.

This was the eighth conventional tug capsize investigated by the MAIB since 1998. Nine people have been killed across those eight accidents.

What is Girting?

Girting — also called girthing — is the specific capsize mechanism that conventional tugs face during assist and escort operations. It occurs when the towline angle increases until the transverse component of the towing force exceeds the tug’s ability to pivot fast enough to realign. The stern is pulled down toward the towline side. The working deck floods. The tug capsizes toward the direction of pull.

Conventional tugs — with a fixed tow hook amidships or aft — are most vulnerable when the towline approaches 90° to the tug’s centreline. At that angle, the entire towing force becomes a transverse heeling load. The tug cannot engine or steer its way out. The only protection is to release the towline — instantly — via the slip hook.

Escort tugs and Voith Schneider propeller tugs use different towing geometry and propulsion arrangements that either eliminate or greatly reduce girting risk. They are not subject to the same constraint. Conventional tugs are, and they remain common in UK port operations.

Eight Accidents Since 1998

The Biter/Hebridean Princess investigation was not the MAIB’s first report on conventional tug girting. It was the eighth. The accidents have occurred across different ports, different operators, and different assisted vessels. The mechanism is the same in each case. The intervention that would have prevented each capsize is the same: release the towline before the heeling moment becomes irreversible.

The MAIB’s decision to accompany its SB1/2026 bulletin with a safety video — rather than a written bulletin only — reflects a deliberate effort to reach operational tug crews in a format more accessible than a PDF. The single recommendation (S2026/122) requires six UK industry bodies to distribute the video to their members, including the British Tugowners Association, UK Chamber of Shipping, UK Harbour Masters’ Association, and the UK Maritime Pilots’ Association.