Ship and Ocean Foundation has been conducting the feasibility study on CIM for shipbuilding and its committee has been establishing a conceptual framework for the CIM for shipbuilding. Now the committee has finished the conceptual design to develop a pilot model and has been prototyping it. The pilot model consists of the systems which will hold the keys to the success of the CIM for shipbuilding. One of the systems being prototyped is a structural design system. This paper reports about an expert system which has one of the functions of the structural design system and which incorporates the design method well-known to hull structural designers as “narai design”. This expert system is applied to the transverse sections in hold part of an oil tanker. The result indicates that the system is applicable to generate the design information necessary to production planning earlier in the CIM for shipbuilding.