The computation procedures of great circ le sailings (GCS) are always the primary task in open sea sailings of voyage pl an. Many artificial judgments needed in calculation and the tedious process make these computation procedures impractical for inexperienced navigators. Besides, most relevant GCS computational programs are lack of completeness and flexibility. It leads to the motivation of this article. Therefore, an integral computation procedure combining the great circle equation method (GCEM) and Napier's rules of right-angled triangles is proposed and then, the Graphical User Interface (GUI) built in the MATLAB(superscript ®) is adopted to develop friendly navigator-oriented GCS program, namely the GCS_Departure. This self-developed program is verified with several examples presented in currently available books.