It is difficult to support collaborative design with a conventional ship CAD system which manages design information using files. In this research, file storage has been replaced with a database. This paper describes the OpenDIS which is an interface between the geometric kernel and the database. Its main purpose is to implement the CAD system which has the STEP database as the native storage. A prototype CAD system has been implemented using that OpenDIS interface which is implemented by OpenCascade geometric kernel and the Objectstore object-oriented database. The STEP methodology is used as the database schema. This CAD system has been applied to the hull design of a ship in order to verify the usefulness of the interface.