This paper relates to steering test results for a super-tanker model with four alternative rudder sizes.The test follows the frequency response procedure which has been developed by the authors. To increase relative rudder size from 1/77 to 1/61 results only a little gain of turning ability and a moderate improvement of stability on course and quick-responsibility in steering. Comparing the present results to Kempf's zig-zag test results for several similar actual ships, it seems that a considerable nonlinear effect is included in a steering motion as hard as usual zig-zag tests.