ABSTRACT
Combined loading presents formidable challenges to the design of multihulls. Without the canon of anecdotal knowledge, legacy designs, and test data that benefits monohull design, significant concerns around multihulls remain open-ended questions. In Lloyd’s Register “Rules for the Classification of Trimarans,” rule load combinations are suggested to ensure that the “hull structure complies … with the [LR] acceptance criteria” (Lloyd’s Register 2017). These eight standard load combination cases were constructed using a deterministic Equivalent Design Wave methodology (Blanchard & Ge 2007). The load combinations, though, do not explicitly include probabilistic aspects apart from the underlying LR Rule assumption (20-year return period, or probability of exceedance at 10–8). Given that the small number of load combinations is a “practical attempt to reduce the number of load cases to a reasonable number,” it is not clear whether these cases are exhaustive when considering an irregular wave environment, nor is the degree of conservatism apparent. Should a detailed probabilistic assessment of lifetime performance be required, it is imperative that the load combination cases are accurate, sufficiently conservative, and exhaustive. In this paper, load combinations are examined using the Design Loads Generator, Aegir, and a copula model for the joint distribution of ship loads.
