The present investigation demonstrates that the estimation of dynamic effects should be included carefully in the analysis of DP performance through model test or dynamic analysis tool where dynamic effect model is included. There are three widely used analysis methods for design and evaluation of DP performance. Dynamic analysis with time domain simulation, static analysis based on mean environmental forces, and model test can be used to analyze the holding capacity of a designed DP system. Among the three analysis methods, the static analysis is most widely used in the design stage. In this paper, heading windows of a 145K shuttle tanker as a holding capacity are evaluated using these three methods. Those three results are compared with each other to investigate reliability of state of the art method. The estimated heading window shows differences depending on analysis methods. The difference was most significant in ballast loading condition, this could be from larger thruster degradation effects. The feasibility of 20% margin in static analysis for dynamic effects was confirmed in some conditions, but some results shows larger dynamic effects in model test.
Recently, the usage of DP (Dynamic Positioning) system is increasing rapidly as deepsea operations are growing up to 3000m water depth. The application of conventional mooring system using chain and wire rope in deep sea has limitations because of economic and engineering reasons, e.g. high costs, high pretension, wide spread area, and so on. Dynamic positioning system automatically controls a vessel to maintain wanted position and heading through active thruster. The DP capabilities to the shuttle tanker have been used in the oil industry for long time, and some information can be found in Bray(1990). The operation of shuttle tanker can be divided into 3 groups; hawser mooring, hawserless mooring, and STL(submerged turret mooring) systems.
