SS: Fiber Moorings, Recent Experiences and Research: Analysis, Design and Installation of Polyester Rope Mooring Systems in Deep Water

The purpose of this paper is to describe the authors’ recent experience with the analysis, design, and installation of polyester rope mooring systems for deep water applications. Among the latest research activities, this article describes a series of full-scale tests performed on polyester rope provided for several spread moored systems offshore Brazil and West Africa. One of the main purposes of the performed tests was to determine non-linear stiffness characteristics of the rope; but other parameters used in the design and optimization of the polyester rope mooring system were also investigated. Introduction The past decade has seen a steady increase in the number of polyester rope deep-water mooring system for oil and gas exploration, especially floating production facilities. Brazil has always been in the frontier of the application of synthetic mooring ropes. Industry forecasts point to a strong increase in the number of such systems, considering the latest deepwater discoveries made offshore Brazil. Due to the past and present history of success in the use of polyester rope for the mooring of deep water floating system offshore Brazil, it is a general consensus that this trend will continue into the future and expand to other producing regions such as The Gulf of Mexico and West Africa as it can already be observed. There are many obvious advantages in using polyester ropes on deep water mooring systems. We could mention a few of them such as: lighter weight, desirable elastic characteristics and superb fatigue performance; on the other hand when engineering and installing such a system there are specific issues to be appropriately dealt with by the designer and the installation personnel. This paper will discuss some of the peculiarities associated to the design; analysis and deployment of polyester rope mooring system for deep water applications. The main topic of discussion in this article is a practical way to model the elastic stiffness of polyester mooring ropes in order to have a simple and reliable model that produces reasonably conservative extreme mooring loads and vessel-offsets. Such numeric model describing the elastic behavior of the polyester ropes have a significant impact on mooring system for floating facilities for deep water applications, with a specific application to the mooring of FPSO’s. Typical Polyester Rope Mooring System for Deep Water FPSO Applications Fig.1 depicts a typical deep water FPSO spread moor system. Each anchor leg is constituted by two segments of chain, one located at the bottom and the second close to the surface; joined by a single or multiple segments of polyester rope. In case of the mooring system shown on Fig.1 we can see three (3) segments of polyester rope joined by two (2) short segments of chain.