202404 - STS bunkering blunder

A tanker was scheduled for bunkering at a deep sea location via an STS transfer. The bunker barge was made fast alongside the tanker and the bunker hose connected, but one of the aft mooring lines parted before the bunkering operation could begin.

While the mooring team was replacing the parted line, the Mooring Master on the bunker barge instructed the tanker to stop engine. This caused the tanker and the bunker barge to slowly turn to port, so that the swell came increasingly on the beam. About 20 minutes later, the tanker’s Master challenged the Mooring Master about the situation, but it was too late. With the swell now nearly on the beam, the rolling action of the vessels occasioned higher stresses on the remaining lines. As the vessels drifted further apart, these lines also started parting.

It was decided to disconnect the bunkering hose and abort the operation, and the teams were instructed accordingly. The tanker crew started to disconnect the bunker hose, but the hose came under tension before all the bolts could be released. As the tension on the hose increased, the disconnection team cleared the area for their own safety. The bunkering hose eventually broke away from the manifold and the hose flange snapped, struck on the hose resting bar and went overboard.

The company investigation found, among other things, that the weather conditions were considered borderline yet acceptable. The swell at the time of the incident was not high enough to threaten the safety of the operation had the vessels kept moving. But once the vessels stopped, they slowly swung perpendicular to the direction of the waves, which led to excessive rolling and much higher forces on the mooring lines. It would appear that the Mooring Master on board the bunker barge displayed poor coordination of the vessels’ manoeuvring and was not properly in control of the situation as the incident unfolded. The Master on the tanker realised too late the consequences of stopping the engine. Additionally, the company checklist seems to have been mis-used by the crew. Such vital items as ‘Is the ship upright and at a suitable trim?, Are mooring gangs in position?, Are berthing and mooring procedures agreed including fender positions and number/type of ropes to be provided by each ship’ were marked as Not Applicable by the Master even though the swell (2m) and bunker vessel size (183m) indicated this particular operation as high risk on the checklist risk matrix.

Lessons learned

• STS operations require good team planning and coordination, on and between both vessels.
• The number and location of all lines and fenders, among others, should be pre-determined for an STS operation.
• Good practices for STS operations can be found in the Ship to Ship Transfer Guide for Petroleum, Chemicals and Liquefied Gas published by Marisec.