The auther had tried a comparison between tank tests and actual ship tests on pitching in high irregular seas. In this paper he tried to analyze the same actual ship tests on bow acceleration speed decrease in heading seas and pitching in following seas. The estimated values from tank tests by means of E. V. Lewis's method on ship motion and Taniguchi, Tasaki and Maruo's method on resistance increase in irregular waves have satisfactorily agreed the actual ship data.