The lengthening of a small chemical tanker: a comparison of class scantling rules

Abstract

The classification societies' rules have been updated and improved dramatically in the last years, crossing from empirically-based and prescriptive rules to more rational rules based on reliability analyses and recommending design criteria rather than codifying design scantlings. However, the complexity of the new rules needs to be faced by computer software issued by the class societies themselves. This article presents the results of some preliminary structural design calculations, carried out according to five different classification societies' rules (BV, DnV, GL, LR and RINA) and using the associated softwares, on a small double hull tanker built in the nineties. In view of the possible lengthening of the ship, the scantling design has been carried out on the midship section, aiming to compare the different rules, requirements and criteria before and after lengthening. An analysis of general check formulations has been firstly carried out, highlighting similarities and differences in the scantling criteria. Then, results of the exercise have been compared to evaluate the best solution for lengthening, and rules requirements have been commented on in the light of the methods and criteria previously reported with the aim to contribute to the rules harmonization process.

Keywords:

• Scantling rules
• classification societies
• comparison
• tanker
• lengthening