The present world experience with open water FPSOs has required more careful considerations towards to the Offloading operation. The multi-environment case, that is when the current, the wind and the waves comes from different directions and they have different intensities, poses to the designers very stringent conditions. For a current only environment, the usual turret position (far ahead towards the bow or far behind towards the stern) is stabilizing for the production ship, what is even improved by the extra effort due to the shuttle ship. Therefore, this stable behavior leads to a almost fixed point about which the shuttle tank is itself stable, just providing the correct hawser length is used. In Campos Basin, Offshore Brazil, this has been known for a long time and the standard full scale offloading is expense supported by towing boats one hundred percent of the time. Meanwhile, this offloading operations are still under analysis for the recently installed turret based FPSOs. The present work supported on ad hoc time-domain simulations and an extended stability theory tries to give some insight to the problem.
The FPSO (Floating Production Storage and Offloading, a floating system which, as the name says, is dedicated to oil production, storage and subsequently for offloading with a more permanent character has been introduced in Campos Basin, offshore Brazil somewhat recently. The first modern system was installed in 1998. Meanwhile, several systems are being installed presently and two are operating routinely in open seas and over deep waters (800 m or more). Among the several key aspects of these FPSOs, one is the offioading process. As shown by (Araujo 1998), it is more cost effective to use Tankers to export production instead of using pipelines and the deepwater situation certainly contributes to this conclusion.
