This paper deals with the results of experiments in which the authors have hitherto measured the twisting moment acting upon the rudder-stocks of five vessels during their turning and backing, together with the other related factors. The data thus obtained were compared with the calculating values by the Jossel's, Beaufoy's, and Akazaki's formulae. The measured twisting moment curves show many newly known phenomena. But the following three features seem to be the most noteworthy. The first is the difference between the maximum values of the twisting moment in port and starboard turning, in spite of the fact that the speed and helm angle were kept the same for both cases. The second is the large fluctuation of the twisting moment, which appeared in hard port turning only. The third is the alternating twisting moment acting on the rudder-stock during backing trial. The authors tried to explain these three interesting features, by assuming the velocity distribution against the rudder in the propeller race behind a vessel.