This paper describes a design model for the conceptual design of ships. Existing design models have problems such that their operating mode of batch versions cannot reflect the design procedures in reality. Reliability of the results is low because the performance estimations are based mainly on empirical formulas. To improve the problems of existing design models, a new design model has been developed. The new model consists of an interactive user interface, a database of main engines, a database of particulars of existing ships, and ten modules for performance estimations. To develop such a user-oriented system, the concept of graphical user interface (GUI) is adopted.