It has been widely recognized that Al technique or knowledge engineering should be incorporated in engineering practice in order to improve product's quality or reduce human labors. Expert systems for supporting ship manoeuvring or subdivision design of tankers have been developed in recent years. The present paper proposes expert system prototype for supporting buckling design of longitudinal strength in bulk carriers, which experienced engineers can perform. In ship design, it is a key role to minimize a routine work composed of analysis and synthesis, so that satisfactory results can be easily obtained by keeping safety of structure. There may be two important difficulties in building a system, that is, efficient data-control supporting re-analysis, and programming of complex ramification for plastic analysis or designer's know-how. This study show the validity of Al technique to resolve these two difficulties and minimize human labor irrelevant to intellectual design practice.