3.4 Relationship Between the Overshoot Angles and the Indices from Auto-tracking Simulation

　

 The relationship between overshoot angles and rudder indices are presented at Fig. 16. At first glance, there seems to be no correlation between them. However, if we look at the ships within a length group, we can find a tendency that the increase of rudder index results in slight increase of the overshoot angles. This tendency is most clearly found from the figure (e). Similar tendency can be found from Fig. 17, which plots the relationship between the overshoot angles and swept-path indices. Table 4 summarizes the correlation coefficients between the overshoot angles and the indices of navigational difficulty. The second overshoot angle for 10°/ 10°zigzag test has the closest correlation with navigational difficulty, but the first overshoot angle for 10°/ 10°zigzag test does not show clear correlation with navigational difficulty. From this, we can conclude that, although the first overshoot angle is a good index to judge the directional stability of a ship, it is not sufficient to discriminate a ship with heavy navigational difficulty.