RIASSUNTO
Surf-riding and broaching in severe following and quartering seas are vital threats for the safety of fast naval and fishing vessels. Excessive roll motions and even capsizing due to lose of stability can occur under surf-riding and broaching. The rudder and its resulting moments are important for the onset of broaching after surf-riding. Thus, the rudder actions under surf-riding condition which lead to ship broaching are identified in this research based on the developed numerical model incorporating the dynamics of rudder and propeller. Numerical simulations on cases with 1, 2 and 3 degree of sudden rudder actions under surf-riding condition are conducted with small and high Froude numbers. It is found that the state of ship motion is not altered by the small rudder disturbance under small Froude number. However, under high Froude number, the state of the vessel is very unstable, and can be easily altered by the small rudder disturbance.