A critical comparison of the scantling rules for shipbuilding issued by classification societies

The present research work starts from the working experience of the Author as field surveyor to a classification society. The rules are the link between theory and practice, between research and in service experience. This role is of paramount importance: on a side, theory allows to develop mathematical models and design methods more and more accurate; on the other side experimental validation is always necessary. In the last years the classification societies rules, especially the structural design rules, have been deeply and innovatively improved and probably the updating process is not completed at all. The first chapter of this work summarizes the hystorical origin of rules and introduces reasons which imposed an evolution, undoubtedly very important for the shipping. After a brief description describing, even from the theoretical point of view, new concepts on which new rules are based on, it seemed appropriate a comparison among the rules of the main classification societies involving both methods criteria and numerical examples. The aim is to evaluate the impact of the rules modifications and to give a state of the art review. This choice revealed even more correct considering that in these months the main class societies are proposing the edition of common rules for ships construction, unconceivable since few years ago. In particular the formulations for structural scantling of ABS, BV, DNV, GL, RINA and, for fatigue checks, also of CCS and NKK, have been compared. After the theoretical analysis presented in chapter 3, some numerical examples are variously examined. They allow to highlight different aspects of the changing and to outline what can be still improved: 1. the midship section scantling of a double hull oil tanker has been scantled according to the old and the new edition of RINA rules, 2. the midship section scantling of three typical ships (a double hull oil tanker, a bulk carrier, a container ship) have been evaluated according to some rules and then results compared and analyzed, 3. a practical design example is presented regarding the lengthening of a chemical tanker according to some classification societies rules, 4. the fatigue checks of a typical detail according to different rules are presented and deeply analyzed, 5. the ultimate strength of the hull girder required by BV and RINA is compared to simplified analytical methods and with an FE model. The last chapter addresses recommendation for further research and conclusion issues.