In its third case of its latest edition of the Safety Digest, the UK MAIB provided information on the risk of vessel girting, during mooring operations, and highlighted the importance of the appropriate training of the crew, in order to prevent such cases. Girting means the risk of capsizing due to high athwart ships towing forces.
The incident
A 2,500gt chemical tanker was berthed port side alongside and had completed discharging its cargo. It was dark, near high water, with good visibility and a force 4 to 5 wind blowing onto the berth. A pilot boarded the tanker in preparation for departure. He advised the master of his intention to use a mooring launch to assist, if necessary, in lifting the tanker’s stern off the berth. The mooring launch, which had a bollard pull of 13t, arrived alongside. Its towline was then passed and secured through the tanker’s starboard quarter fairlead.
Indicative relative movement of the mooring launch. Credit: UK MAIB
Using port rudder, ahead propulsion and starboard bow thrust, the pilot manoeuvred the tanker bodily off the berth with only the forward spring still secured ashore. The forward spring was then let go and the tanker was manoeuvred ahead. The pilot ordered the launch coxswain to run with the tanker and then, to approach the tanker and let go. Both orders were acknowledged by the launch coxswain, who was attempting unsuccessfully to turn the launch to port.
Load had come onto the towline, causing the launch to list heavily to port. The coxswain then attempted to operate the towing hook emergency release, by pulling on the handle suspended from the wheelhouse deckhead.
Meanwhile, on being notified by one of his crew that the mooring launch was in difficulty, the tanker’s master brought the propeller pitch to zero. The launch then capsized, with the towline remaining attached to the tanker. Although the launch deckhand was able to swim clear, the coxswain remained trapped in the wheelhouse, until he was sighted and rescued over an hour later.
Lessons learned
UK MAIB summarized its conclusions on this case, providing advice for future operations:
A gog rope is commonly used to move the effective towing point closer to a towing vessel’s stern. This prevents the towline from being taken across the towing vessel’s beam, and therefore reduces the danger of girting. The mooring launch’s management company recognised the danger of girting and, consequently, required a gog rope to be used on every tow. However, it incorrectly assumed that the mooring launch crew were proficient in adjusting the gog rope to maximise its preventive effect.
In this case, the gog rope was set at an intermediate length that was neither short enough to move the towing point sufficiently aft to prevent girting nor long enough to facilitate the coxswain’s intended turn to port once load had started to come onto the towline.
A thorough assessment of the task prior to commencement, underpinned by appropriate training, highlighting the risk of girting and how to prevent it, would have enabled the mooring launch coxswain to make a more informed decision on what the optimum gog rope arrangement should have been.
Effective proactive communications between the tanker’s pilot and the mooring launch coxswain at defined stages of the operation would have reduced the risk of girting. In this case, the pilot relied on the coxswain to act autonomously and to inform him when in doubt or difficulty. Had the launch coxswain been warned that the tanker was about to be manoeuvred ahead or had already started to move ahead, he might have been able to turn the launch to port before additional loading came onto the towline. Alternatively, he could have informed the pilot of any doubt he might have had in his ability to turn the launch before the tanker gathered headway. The need to establish communications, agree a plan and continually exchange information, including engine movements, is promoted in the Code of Safe Working Practices for Merchant Seafarers and has been a significant finding in a number of MAIB safety investigations concerning towing operations.
With no mechanical assistance, the towing hook emergency release relied on the crew to operate the manual pull in order to release the towline. Tests of the towing hook following the accident demonstrated that, under load conditions, a steady pull required significantly more force to operate the release mechanism than a sharp pulling action, and that the required effort increased in proportion to the loading on the hook. The emergency release had not been practised as part of a drill, and so the crew lacked preparedness to take appropriate and rapid action in the event of a developing emergency.
