200855 Mooring failure, pollution

Source: IMO Flag State Implementation Sub-committee 11

An oil tanker was moored to, and discharging to, a single point mooring (SPM) buoy. At some time during these operations, the chain stopper opened and the chafing chain was released. The ship was then moored only by a pickup rope that parted shortly thereafter. As the vessel drifted from the monobuoy, the cargo hoses parted and approximately 12 tonnes of oil spilled into the sea.

Root cause/contributory factors
The bridge monitor that was used to control the cargo operation also used the same function keys to control different operations. The screen colour was different for each operation; however, the function keys and their sequence were not unique to a given operation.
It is believed that one of the officers performing cargo operations unintentionally opened the chain stopper and released the chafing chain while attempting to secure a forward hydraulic pump.
The function key sequence was the same for each operation and only the screen colour provided an indication as to which operation was being performed.

Lessons learned
Ergonomics, in the form of operator-machine interface, can be a critical element in shipboard safety.
Ships' crews should display warning signs where there is a possibility of confusion in the operator-machine interface.