Abstract: Objectives To improve convergence in underactuated ship trajectory tracking under unknown disturbances, control saturation, and imaginary term generation in conventional fast terminal sliding mode methods. Methods Transform the tracking problem into following a virtual ship's speed. Use a saturation function in the control loop, design a new global fast terminal sliding surface, and employ a nonlinear disturbance observer for compensation. Results Simulations confirmed robustness against unknown time-varying disturbances without imaginary terms. Tracking convergence improved by 9.62% and 33.80%, longitudinal velocity error reduction reached 49.43% and 51.11%, compared to second-order sliding mode controllers and conventional nonlinear sliding mode controllers. Conclusions Results show the designed novel global fast terminal sliding mode controller for trajectory tracking outperforms the second - order sliding mode controller and ordinary nonlinear sliding mode controller, offering a new approach for trajectory tracking control.