Up to very recently the design of mooring systems and flexible risers lacked an adequate approach to account for dynamic effects in the extreme load assessment. Usually the design concept was based on the extreme positions of the floating structure. Recent research has indicated that the dynamic amplification of the tensions in the lines and risers can be of the same order of magnitude as the co-called quasi static values. Also it has been concluded that the dynamic effects in the mooring system can affect the low frequency motions of the structure by the increase of virtual stiffness and damping.In this paper newly developed 3D computational procedures are presented, describing the motion, tension and bending moment along a flexible pipe or a mooring line. Also correlations with model test data are discussed.