IMCA Marine Division

Publication Details

Quantified Frequency of Shuttle Tanker Collision During Offtake Operations

Shuttle tankers have been growing in importance in the oil production industry. In 1995, offshore loading systems were used to transport 36% of crude oil in the North Sea. By the year 2000, offshore loading into shuttle tankers is likely to account for 47% of the North Sea’s total production, and this trend is being repeated globally. In the European area, the main growth is likely to be in the Norwegian Sea and the Atlantic Margin. With this in mind, IMCA commissioned this report to investigate the reliability and risk of station keeping failure of FPSO and shuttle tankers during offtake operations.

The study examined the station keeping data on tanker offloading operations that were supplied to IMCA. A total of 156 incidents were analysed of which 12 involved a collision between the shuttle tanker and the loading point it was using.

The data are considered to be comprehensive for major DP incidents and DP exposure time. Data on non-DP offtake operations were also collected but these are not so comprehensive because the loading times and associated incidents are incomplete.

Fault trees for the 12 collisions show that the causes can be grouped into three areas:

• position references
• main engine/propeller
• DP operators

Nearly all the incidents refer to equipment failure. It is also clear that there is a great deal of under reporting of near-miss incidents. This is dramatically illustrated by the reporting profiles of tankers for the year before and after a collision.

The report concludes that there are still lessons to be learned, but none of the problems are insurmountable. Areas where scope for improvement has been identified include incident reporting, management of change and operator training.