ABSTRACT In Order to fulfill the requirements of the German offshore wind industry individually designed and constructed offshore wind farm installation vessels are needed. One of the primary design constraints of these ships is dynamic positioning (DP). For the correct design of DP systems static and dynamic calculations should already been performed during the early ship design. Among other input data time series and time averaged mean values of the horizontal wave drift forces as well as the wave drift yaw moment are needed. For this a calculation procedure based on strip theory in combination with a correction for short waves is presented and validated with experimental results for the SIETAS TYPE 187.weiterlesen