In the past, the reduction of the pitching motion of ships by means of the anti-pitching fins at the bow has been analyzed. What seems to be lacking, however, is the analysis of the anti-pitching fins at the stern. This paper evaluates the effect of the anti-pitching fins at the stern from the viewpoint of passengers' comfort. The impulsive force on the stern fin is smaller than that on the bow fin in slamming conditions. Model experiments were conducted to evaluate the effect of our anti-pitching fins on ship motions. The anti-pitching fin at the stern reduced vertical acceleration by 0.05g in head seas, with a significant wave height of 2.0m. The new method for evaluating passengers' comfort consists of exposure duration and amplitude and frequency of acceleration. These are based on questionnaires given to passengers and measured ship motions of the training ship Kagoshima-maru. The correlation coefficient between the method and the questionnaires is 0.71. We can mention that the method is reliable for evaluation of passengers' comfort.
Wave length in the coastal sea is usually 1 or 2 times as long as the length of small vessels. This is a severe condition for the pitching motion of small vessels. Since it is hard to improve the pitching motion of ships after delivery, the seakeeping quality of ships should be evaluated in the initial design stage. The reduction of the pitching motion of ships by means of the anti-pitching fins at the bow is analyzed both qualitatively and quantitatively, through theoretical and model experiments. Abkowitz (1959) pointed out problems associated with the use of the anti-pitching fin at the bow, which include the hull vibration, the large impact force in slamming conditions and the extra resistance of the anti-pitching fin.
