This paper proposes an event-triggered course-tracking control approach of marine surface vessels based on output reference tracking method. Throughout this work, a reference system, which consists in the continuously controlled version of the system understudy, is employed. Based on the difference between the state of the event-triggered system and that of the reference system, a Lyapunov-like function is defined to guarantee the boundedness of the tracking error. The proposed strategy reduces the amount of energy consumption and computation, thus results in less controller executions, and its feasibility is further verified by the exclusion of Zeno behavior. Effectiveness of the proposed algorithm is further illustrated by simulation results.