This paper relates to Kempf's zig-zag test results for a super-tanker model with several alternative rudder sizes and a special rudder arrangement shown in Fig. 8, following the preceding papers published in the journal of the Society of Naval Architects of Japan, No. 103, 1958. The results are analyzed in terms of the steering quality indices which has been developed by the author and published in the I. S. P. Nr. 35, 1957. This procedure provides a successfull investigation for the effect of relative rudder size on steering quality. It should be noted that a considerable reduction of steering quality indices K and T with increase of turning angular velocity is experienced.