The robustness of nonlinear ship motion phenomena, as regards hydrodynamic loads’ modeling assumptions, is explored. The focus of the work is on a certain type of extreme dynamic behavior in following/quartering waves, known as cumulative yaw, which is a dangerous gradual build-up of yaw’s amplitude, explained dynamically as a manifestation of parametric instability for yaw motion. It is classified as an alternative mechanism of broaching, exhibiting a nonlinear signature that is believed to be distinctive from that of the classical broaching triggered by surf-riding. First-order wave loads are considered, including Froude-Krylov and two alternative forms of diffraction, while for hydrodynamic reaction and rudder, a classical fully non-linear surge-sway-yaw mathematical model of maneuvering motions in regular astern seas is employed. The numerical investigation relied mainly on the continuation technique that can efficiently capture a dynamical system’s bifurcations and stability boundaries. It was supplemented with selected simulations. This study confirms that the nonlinear phenomena relating to cumulative yaw are robust with respect to the method of calculation of wave loads. They can be considered as features of extreme ship motion behavior.