The Rope That Decides Whether a Tug Capsizes: A Working Guide to Gog Ropes

Why This Guidance Exists

On 24 February 2023, the tug Biter girted and capsized off Greenock while assisting the passenger vessel Hebridean Princess, killing two of its three crew. The MAIB's investigation (Report 17/2024) and subsequent Safety Bulletin (SB1/2026) are already covered in depth elsewhere on this site. What followed the investigation is less widely known but just as practical: in 2025, the British Tugowners Association (BTA), the UK Maritime Pilots' Association (UKMPA), and the Workboat Association (WA) jointly published "Gog Ropes: Industry Advice" — a working guide aimed squarely at tug masters, crew, pilots, and port authorities, built specifically off the Biter case. Biter was not an isolated event either: it was the eighth conventional tug capsize investigated by the MAIB since 1998, following Trijnie (1998), Ijsselstroom (2010), Chiefton (2011), and Domingue (2016) among others, with nine lives lost across those eight accidents.

What a Gog Rope Actually Does

On a conventional tug, the towing point sits near midships, with the tow hook typically free to swing both horizontally and vertically. That arrangement is fine while the towline stays roughly fore-and-aft — but if it swings toward the beam, the entire towing force becomes a heeling moment the tug may not be able to counter. That's girting (also called girding or tripping): the tug is dragged sideways by its own towline, and it can happen in seconds, often too fast for the crew to release the tow before the heeling force passes the point of no return.

A gog rope (also called a gob rope) shifts the effective towing point aft, toward the stern, converting what would be a heeling moment into a turning moment the tug can actually work with. It runs through a staple or gog eye, ideally at deck level and close to — but above — the waterline, and its length is typically controlled by a gog winch operable from the wheelhouse, which also reduces the need for crew to handle gear that's under tension.

Treat It as a System, Not a Rope

The joint guidance is explicit on this: the gog rope, winch, staple, bollards, shackles, and emergency release together form a system, and every part of that system needs the same discipline — inspection before and after use, a dedicated rope used for no other purpose, known SWL and MBL for every component, a retirement schedule, and a towing log recording when and why the gog was used. A gog rope that's been pressed into service as a spare line for something else, or that no one has checked the breaking strain of against the towline it's paired with, is not a working safety system — it's a rope that happens to be rigged in the right place.

Speed Is the Multiplier

The guidance cites US Coast Guard research (NVIC 12-83) showing that towline heeling force scales with the square of towing speed. In practical terms: the heeling moment at 4.6 knots is roughly five times what it is at 2 knots, and more than double what it is at 3 knots. Stern towage should ideally be conducted around 2 knots, including the connecting phase, and conventional tugs are at increased girting risk above 3 knots STW. This is not a minor technicality — it's the single biggest lever available to a tug master and pilot for keeping a margin of safety, and it's controllable in a way that gear condition sometimes isn't.