Maneuvering Model for FPSOs and Stability Analysis of the Offloading Operation

Abstract

The discovery of new fields in deep water brought back the use of large ships such as FPSOs. This seems to be the trend toward ultra deep water units at least in offshore Brazil. At about the same time, VLCCs (very large crude carriers) have been converted to work as FPSOs. However, working as a stationary unit a VLCC presents directional stability problems. In the present paper a methodology is discussed to develop a mathematical model for the simulation and the verification of the stability of a VLCC working as a FPSO. To express the forces and moments acting on the ship hull the results of a group of experiments are described in the classical sense of the maneuverability theory, although they concern large angles of attack and low advance velocity. Besides, a procedure to determine the stability of the floating system is also presented. This is based on local analysis and follows the classical theory of dynamic systems. Further, the use of stabilization devices for a floating unit and the offloading operation are discussed. Finally, an experimental test is proposed, in order to take into account scale effects.