The FPSOBR concept was developed to be an oil production unit that will be moored in a location for nearly twenty years. We have strived for a unit easy to construct, simple to operate and with low motions at sea, in order to minimize the loads on the production risers and mooring system. Analizing the performance in waves of actual FPSOs operating in Campos Basin revealed the roll motion to be the biggest concern. Single amplitudes of up to seventeen degrees have occurred in swells of four meters of significant wave height, implying in more expensive oil process plants, and less comfort for the crew.

In the FPSOBR design, the restoring characteristics of the ship have been reduced in comparison with regular ships of similar displacement. This approach worked regarding the roll motion characteristics, where a small reduction on the ship’s beam implies in lower metacentric height and large natural periods. The heave and pitch motions are similar to the existing FPSOs. This work concerns with the validation of the computed first order ship motions, through comparisons with measured results in the IPT (Instituto de Pesquisas Tecnológicas) model basin. It is shown that though the regular wave results compare very well with computed first order motions, the irregular wave tests showed the occurrence of second-order slow-roll motions for extreme sea conditions.

The reasons that gave rise to this phenomenon are discussed, as well as its implications in the current design process.