This paper summarises the main results of experimental tests conducted at the Danish Hydraulic Institute in the frame of the EU-TMR-LSF project "A New Concept of Catenary Mooring System for FPSO". The main interest of this research project is the analysis of the behaviour of a proposed mooring system for FPSO well suited for weather conditions characterised by a dominant swell and current and by a moderate almost perpendicular local sea and wind. The basic idea of this mooring design is to join the best characteristics of the turret and spread mooring systems to allow the FPSO to move within a specified offset so that the wave loads on the lines and on the vessel can be minimised. The experiments and the related analysis refer to the dynamic behaviour of the FPSO alone and FPSO+Shuttle tanker during offloading, in extreme and operational weather conditions respectively.
Since the last few years, the interest of the offshore industry is mainly addressed to the deep and very deep waters. The exploitation of oil and gas fields in deep waters can be performed either by floating production systems or by subsea production systems, the limit of fixed structures being in the range 200–300 m. The Floating Production Storage and Offloading (FPSOs) are among the most popular floating production systems for both economical and technical reasons. They are in moderate wave climates usually represented by a conventional tanker properly modified for offshore operations and moored by means of catenary lines. Since many recent developments are located in West Africa sites, characterised by mild environmental conditions and dominant wave, current and wind directions, the authors propose a particular spread (no turret) catenary mooring system, having a weathervaning behaviour limited to the sector of prevailing environmental actions.
