This article presents the development, implementation, and comparison of two trajectory tracking nonlinear controllers for underactuated surface vessels. A control approach capable of stabilizing all the states of any planar vehicle is specifically adapted to surface vessels. The method relies on transformation of the six position and velocity state dynamics into a four-state error dynamics. The backstepping and sliding mode control laws are then derived for stabilization of the error dynamics and proven to stabilize all system states. Simulations are presented in the absence and presence of modeling uncertainties and unknown disturbances. An experimental setup is then described, followed by successful experimental implementation and comparison of the two controllers.
