API RP 2SK:2005 (R2015)

The purpose of this document is to present a rational method for analyzing, designing or evaluating station-keeping systems used for floating units. This method provides a uniform analysis tool which, when combined with an understanding of the environment at a particular location, the characteristics of the unit being moored, and other factors, can be used to determine the adequacy and safety of the mooring system. This document addresses station-keeping system (mooring, dynamic positioning, or thruster-assisted mooring) design, analysis, and operation. Different design requirements for mobile and permanent moorings are provided. The design procedure specified in this document is based on a deterministic approach where the mooring system responses such as line tensions, vessel offsets, and anchor loads are evaluated for a design environment defined by a return period. The mooring system responses are then checked against the mooring strength, offset limit, and anchor capacity to ensure a factor of safety against mooring breakage or excessive vessel excursion. It should be noted that mooring designs based on this approach may not have the same level of reliability, as discussed in Appendix G. The technology of mooring floating units is growing rapidly. In those areas where data considered adequate were available, specific and detailed recommendations are given. In other areas general statements are used to indicate that consideration should be given to those particular points. Designers are encouraged to utilize all research advances available to them. As offshore knowledge continues to grow, this document will be revised. It is hoped that the general statements contained herein will gradually be replaced by detailed recommendations. This document does not address mooring inspection/maintenance requirements and synthetic fiber rope mooring. These issues are addressed in the following API documents: -- API RP 2I, Recommended Practice for In-Service Inspection of Mooring Hardware for Floating Drilling Units (Reference 1). -- API RP 2SM, Recommended Practice for Design, Manufacturing, and Maintenance of Synthetic Fiber Ropes for Offshore Mooring (Reference 2).