As oil exploration and production is moving into greater water depths there is a need for cost effective station keeping systems. To date all floating production units have used conventional catenary mooring systems consisting of chain or a chain/wire combination. For greater water depths the use of a catenary mooring system (CMS) will result in very long lines and a large additional vertical load on the platform. The objective of the present work has been to develop cost effective stationkeeping systems for floating production units in 500 • 1500 m water depth. The work is based on a case study of a large steel floater (semi). A conceptual design of a taut mooring system (TMS) has been developed. This investigation has focused on the dynamic behavior of the TMS in order to document acceptable dynamic performance. A taut mooring system based on a polyester fiber rope offers an alternative. For a water depth of 1200 m the line length is reduced from 3100m to 2030 m and the footprint is reduced from 2800 m to 1700 m by using a taut mooring system instead of a catenary system. In addition, a taut mooring system using polyester ropes is significantly more cost effective than a conventional catenary mooring system at large water depths. As an overall conclusion the investigation has confirmed satisfactory behavior of the proposed TMS concept.
The drive to exploit hydrocarbon reserves in ever deeper waters has forced designers to extend the limits of proven station keeping solutions. The majority of spread mooring systems used in the past decades were for relatively shallow waters. Only in the past ten years, has the success of deep water exploration programs has confirmed the need for permanent mooring systems in water depths well beyond the continental shelves.