3.3 Evaluated Rudder Index and Swept-Path Index

　

 Fig. 13 and Fig. 14 show the calculated rudder index and swept path index for the forty ships respectively. Fig. 15 shows the averaged indices for the four length group. Two clear tendencies can be seen from these figures. As the given mission become complex, both RI and SI are increased, and, as a ship becomes large, both indices are increased. Furthermore, we can see that the difference in L/U does not play a decisive roll in the determination of RI and SI. Many ships in group 2 and group 3 are overlapped between 30 and 40 of L/U value, but ships in group 3 clearly have the larger SI and RI value. Furthermore, a ship within group 3 has exceptionally large L/U value, but the calculated indices are almost similar or even smaller than other ships within the same group. This is somewhat contradictory to the IMO criteria for overshoot angles. According the IMO resolution, a ship with the smaller L/U should have the smaller overshoot angles, and this means that the smaller ships should satisfy the severer standard. In some sense this resolution may have a meaning that the smaller ships usually navigate the coastal area and the possibility of marine casualty in this area is higher than others due to heavy traffic. However, when we consider the navigational difficulty, current criteria for the small ships seems to be too severe.