According to the ABS Guide for Building and Classing FloatingProduction Installations (ABS, 2009), the design criteria to reflect the site-dependent nature of a ship-type Floating Production, Storage and Offloading (FPSO) system can be accomplished through an introduction of environmental severity factors. These factors are introduced to adjust the North Atlantic unrestricted service load and fatigue damage requirements that apply to a trading vessel to the siteand route-specific service conditions for the specific FPSO installation. The two types of environmental severity factors, labeled as the a- or b- type, are defined to account for the effects of wave condition on fatigue damage and dynamic loads, respectively. To accommodate this concept, ABS has developed the Sea Environment Assessment System (SEAS) as a part of the analysis modules in the ABS Eagle FPSO software. This paper provides technical background information about the SEAS concept and its criteria for determining the environmental severity factors that are applied for the evaluation of FPSO hull structural scantling strength. The criteria that can handle complicated wave conditions in a region where both sea and swells exist simultaneously and propagate in different directions are also addressed.


Knowledge of winds, waves, currents, tides and other environmental factors is crucial for a reliable design of a floating structure such as an FPSO. The proper sea environment assessment should be made for several sea environmental conditions pertinent to FPSOs. Depending on the FPSO type, i.e., a new build FPSO, an existing FPSO expected to move to another site or an existing tanker converting to an FPSO, it may have four different sea environment situations, i.e., intended site for operation, transit from building location to the operating site, historical sites for past operation and historical routes for operation as a tanker.

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