Barge-shaped FPSO (Floating Production, Storage and Offloading) units are the most favored and adopted development choices in the oil and gas development offshore West Africa, and to a less degree offshore Brazil and in South China Sea as witnessed by the recently completed projects over the last several years.

To keep the facility in position, either a spread or turret mooring system has to be designed, fabricated and installed. The first step in mooring system design is to size the mooring lines which rely on accurately predicting the current, wind and wave forces. Due to the complexity of topsides and the uncertainty in predicting the forces numerically, physical model tests are most always carried out.

In this paper, a simple, elegant and cost-effective numerical approach is presented and validated to predict the current loading. Comparison between previous model test data and numerical results showed excellent agreement for various operating conditions and for transit condition. It is discovered that to correctly assess the yaw moment on a FPSO, the Munk moment on a FPSO has to be properly accounted for in this numerical approach. The accurate way of estimating the Munk moment is discussed.

It is concluded that the proposed tool, simple but elegant, is very cost effective in accurately assessing the current loading on a barge-shaped FPSO, and thus, is a valuable tool for PRE-FEED, and/or FEED, or even Detail design phases of a barged-shaped FPSO project.

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