This paper outlines the potential advantages of using lightweight fiber ropes for mooring floating production platforms. The influence of tether properties on mooring system response is discussed. It is shown that a comparison of alternative ropes in terms of their mechanical properties is inadequate; relative merit can only be assessed through comparison of full systems that have been designed to minimum cost, and to common performance specifications. For catenary systems, it is found that a lightweight option using polyester fiber can outperform both traditional and more exotic solutions. The significant mechanical performance characteristics governingmooring systemsdesign have been measured for a model tether.

This paper describes the experience of Petrobras in the design, installation and operation of deepwater mooring systems incorporating high efficiency polyester fiber ropes. These ropes have been used now for more than 12 years in catenary and taut configurations to moor drilling and production units as well as storage and offloading facilities. The paper provides a history of the development of this technology, highlighting the key issues involved in introducing in mooring systems a component that has non-linear visco-elastic behavior. Differences to all steel systems in terms of: behavior, failure modes and design criteria and procedures are discussed. The paper presents the life cycle management strategy adopted by Petrobras in the early years of the use of this technology and its evolution that have guaranteed that the only failure mode observed over all these years was mechanical damage. It is expected that this paper shows that the use of polyester (polyethylene terephthalate) ropes in deepwater moorings is a mature technology.

This paper describes a development program being conducted by Petrobras to develop reliable and through life cost effective moorings for depths to 3,000 m. Four alternative solutions are considered: spread catenary, taut leg, taut with submerged buoys and differentiated compliance (DICAS) mooring systems. For each system, four main aspects are being investigated: materials, design procedure and criteria, installation and maintenance. This program has started in 1996. Results already obtained show that: its is economically feasible to moor exploration and exploitation floaters in water depths to 3,000 m. The paper also discusses the most cost effective options for these moorings and key parameters to select, design, install and operate them.