Structural scantling of yachts: different direct calculations vs. numerical analysis

Abstract

Nowadays yacht’s superstructures represent a real complex problem to structural engineers. Ship’s structural calculations already constitute a difficult task, but when it comes to yachts the level of compromise for this design field is increased. Since the main purpose of these type of ships is usually leisure, the general arrangement, aesthetics and clients requirements are prioritized. Therefore, the yacht structure needs to fulfill these constraints and, actually, enable most of them. This fact is amplified for the superstructure area. The most common desired large windows, open spaces, pools and jacuzzi are only possible because of the complex structure behind it. In this work, the superstructure of a real yacht is analyzed in terms of two different classification societies: Lloyd’s register and ABS. The first part consisted into performing rule-based calculations in order to verify and compare both register’s requirements. To achieve that two python codes were created based on each classification society rules. In the end, it was also possible to implement an optimization procedure in order to obtain the lighter structural design possible for the study case. The comparisons shown that LR is more severe for safety coefficients, but ABS compensates that with higher requirements for design loads. Finally, the second part of the study was to perform a finite element analysis for the optimized structure. The idea was to evaluate the proposed design in terms of its structural reliability and to comprehend if there was space for further improvements. The FEA was performed for the deck pressures load case. The results were positive for most locations, and shown some localized problems. Specific locations appear to need local reinforcement, while other would require geometrical smoothing. At last, it was possible to state that a satisfactory design was proposed. Future works could involve, however, other load cases to evaluate possible different weak locations. Keywords: classification society, direct calculation, finite element method, finite element analysis, python, rule-based design, yacht structural design.