The 1st Edition of API RP 2SM — Recommended Practice for Design, Manufacture, Installation and Maintenance of Synthetic Fiber Ropes for Offshore Mooring — was released in March 2001. Prior to then, most of the actual synthetic fiber rope mooring applications were installed in Brazil by Petrobras. Since the publication of RP 2SM, polyester moorings have been used in other deepwater basins, including the Gulf of Mexico, for both temporary drilling MODUs and permanent FPSs. Much has been learned from the actual design, manufacture, installation and operation of these systems by other operators and contractors throughout the past decade. This work has created an extensive knowledge base in the areas of both synthetic fiber rope behavior and mooring system design. To best capture these new learnings, an API Task Group assembled to perform a major update in developing a 2nd Edition. API RP 2SM is the recognized standard for synthetic fiber offshore moorings in the Gulf of Mexico as well as other deepwater basins of the world. It is used in conjunction with API RP 2SK (Design and Analysis of Stationkeeping Systems for Floating Structures, 2005) and API RP 2I (In-Service Inspection of Mooring Hardware for Floating Structures, 2008) for the design, manufacture, installation and maintenance of both temporary and permanent synthetic fiber mooring systems. This paper will present the key changes in the update of this API RP. Reasons for the changes and significance on a synthetic fiber offshore mooring project will be discussed. Major changes in the RP include sections on elongation and stiffness testing, contact with the seafloor, creep rupture and axial tension compression fatigue. The new guidance in the RP will allow for improved synthetic fiber mooring systems design, installation and operation while also potentially reducing cost. Introduction In 1997, Petrobras installed a 12-point taut leg polyester mooring system on its P-27 semisubmersible floating production system in the Campos Basin, offshore Brazil. This installation was a first in the offshore industry, and since then Petrobras has installed more than 20 polyester mooring systems on semis, FSOs and FPSOs. In 2004, BP was the first to install a polyester mooring system in the Gulf of Mexico (GoM) on its Mad Dog spar. Anadarko followed shortly by installing a polyester system on its Red Hawk cell spar. Since then several other projects (Gomez, Tahiti, Blind Faith, Independence Hub, Thunder Hawk, Mirage and Perdido) have used polyester mooring systems in the GoM. Polyster moorings are planned for future GoM projects, including Petrobras's Chinook and Cascade development. Additionally, polyester has been used for the Kikeh spar moorings in Malaysia as well as several CALM buoy moorings and turret moorings throughout the world. Similarly on the MODU side, in 2001 both Shell and BP successfully performed a full scale field trial of polyester mooring systems from a MODU. Since then, such systems have become more commonly used. In particular, after the 2004 and 2005 hurricanes, the use of polyester mooring on the MODUs has greatly increased as a possible means to mitigate overload failure or damage to infrastructure on the seafloor should a mooring system failure occur and the MODU go adrift during a hurricane.

Spread moored floating production platforms are employed worldwide in the exploitation of offshore hydrocarbons. To date they have all employed catenary spread mooring systems (CSMS) using chain or combination wire/chain components. In water depths to 1500 feet and beyond, such simple wire/chain systems become increasingly inefficient and costly. To improve cost efficiency, tighten watch circles and 10wer vertical load on the platform several innovations have been introduced such as the use of submerged spring buoys (Ref. I), ground wire, and ropes made from synthetic aramid fiber. An aramid rope has yet to be employed in a permanently spread moored production platform as industry awaits a better understanding of the long term behavior of this material (Ref. 2). The installed cost of a deep water (XM remains high despite these innovations and a need exists for even more efficient spread moorings as industry looks to water depths of 3000 feet and beyond. The most promising alternative to the (XM to emerge in recent years is the Taut Leg Spread Mooring (TLSM) system, with short scope legs (Fig. 1) and where vertical uplift on the anchors is permitted (Ref 3, 4). This paper explains the operating principles of a TLSM, its performance sensitivity to variations of key parameters and shows the cost benefit versus a CSM by specific case studies. FUNDAMENTAL BEHAVIOR EXPLAINED To develop a cost efficient design, it is essential to understand the basic mechanisms by which a TLSM resists platform mean loads and wave induced motions. The behavior is most easily grasped by studying the simple taut leg system shown in Figure 2. k consists of a light weight, elastic mooring leg in water depth D stretched between the anchor point A and the fairlead point F separated by a horizontal distance L. The anchor point is fixed and resists horizontal and vertical forces. As the fairlead point translates away from the anchor point in response to an applied mean load, tension is induced in the leg as it stretches elastically between the points. An equilibrium position is attained when the moment created by the horizontal force components (H *D) is balanced by the moment created by the vertical force couple (V*L) between the anchor and fairlead points. As the line slope angle relative to the horizontal decreases, distance L increases requiring a smaller vertical force and therefore smaller line tension to resist a given horizontal force. However, line scope and therefore cost also increases. If horizontal force per unit of line volume is used as a measure of cost efficiency, it can be demonstrated that the most cost efficient line slope of a simple TLSM to resist a horizontal mean load is 450 (scope/depth ratio of 1.414). In a catenary system, mean offset is controlled by line weight and pretension. Lines composed of materials with lighter weights and with larger pretensions produce.

This paper presents the results of aerodynamic and hydrodynamic model tests of the ENSERCH Garden Banks, a semisubmersible Floating Production Facility (FPF) moored in 2, 190-ft waters. During the wind tunnel tests, the steady component of wind and current forces/moments at various skew and heel axes were measured. The results were compared and calibrated against analytical calculations using techniques recommended by ABS and API. During the wave basin test the mooring line tensions and vessel motions including the effects of dynamic wind and current were measured. An analytical calculation of the airgap, vessel motions, and mooring line loads were compared with wave basin model test results. This paper discusses the test objectives, test setups and agendas for wind and wave basin testing of a deepwater permanently moored floating production system. The experience from these tests and the comparison of measured tests results with analytical calculations will be of value to designers and operators contemplating the use of a semisubmersible based floating production system. The analysis procedures are aimed at estimating 1)vessel motions, 2)airgap, and 3)mooring line tensions with reasonable accuracy. Finally, this paper demonstrates how the model test results were interpolated and adapted in the design loop. INTRODUCTION ENSERCH Production Operating Limited Partnership (EPO) has selected the Glomar Biscay I, an Ocean Victory-class semisubmersible MODU for conversion to the FPF and renamed it the ENSERCH Garden Banks. The FPF will be located in Garden Banks Block 388 in the Gulf of Mexico in 2,190 feet of water. The FPF will be permanently moored using a 12 point combination chain and wire rope system. The mooring system is designed for the 10o-year hurricane condition at the site. In this paper results of 1) wind tunnel testing, 2) global performance analysis, 3) mooring system design and analysis, 4)wave basin model testing, are presented. DESIGN PREMISE The mooring system has been designed according to practices and procedures recommended by ABS [1] and API [2]. Mooring design criteria are summarized in Table 1. The worst one-line damage condition was determined by analyzing cases with either the most loaded line or the second most loaded line broken. Mooring Line Scope The mooring line scope was designed to ensure no uplift of the mooring line at the seafloor in the 10o-year storm condition with all lines intact. Also, no mooring line was allowed to contact an environmentally sensitive seafloor area within the mooring pattern. Platform Offset Requirements The vessel offset requirements used in the mooring system design for the ENSERCH Garden Banks are shown in Table 2. Metocean Criteria The following three conditions are used to design the permanent mooring system:1ao-year hurricane survival condition,1a-year winter operating condition and5-year winter storm combined with loop current operating condition. Metocean criteria for a similar region (27º N and 86º W) of the Gulf of Mexico, studied by API and presented in [3], suggested that a set of reduction factors may be applied to the omni-directional wave height to account for the directionality of the severest hurricanes in this region.