-The effect of the lift force acting on rudder,

 Fig.8 shows the comparison of the results in three cases for the lift force acting on rudder. In Case (8-a), the rudder has original rudder area and rotates to 20 degrees from neutral position, this lift force is the smallest in these cases. In Case (8-b) the rudder has original area and rotates to 35 degrees, in Case (8-c) the rudder has two times large area as original and rotates to 35 degrees.

 In case a ship starts to turn in head or following sea, if the rotating angle or the area of rudder is too small, the rolling amplitude tends to grow large relatively In the wave condition of Fig.8, this ship has resonant rolling oscillation with encounter frequency of wave in quartering sea. Therefore, if it takes long time to turn, the rolling amplitude grows. This result suggests the advantage of using high lift rudder, for examples flapped rudder or shilling rudder, to prevent the large amplitude rolling or to make quick turn.