<p>This paper investigates the quantized tracking control of the underactuated surface vessel subject to external disturbances and deferred partial state constraints. To break through the control limitations of underactuated systems and separate the constrained partial states, a nonlinear transformation is introduced to convert the underactuated surface vessel system model into a fully actuated one. In order to enhance control precision and anti-disturbance capability, a dedicated disturbance observer is constructed for real-time estimation of external disturbances and an equivalent decomposition technique for quantized control inputs is proposed to mitigate quantization errors. Subsequently, a systematic tracking controller is designed to ensure that the specified partial states strictly adhere to predefined deferred constraints, while enabling the system output to achieve practical tracking performance. Compared with existing literature, the proposed control strategy achieves a dual breakthrough (i.e., the stability of the closed-loop error system and the boundedness of closed-loop signals)-a performance integration rarely achieved in existing studies. Simulation results validate the effectiveness and feasibility of the proposed approach.</p>