Parametric Evaluation of Wet Deck Geometry in an Early-Stage Design for Large Sailing Catamarans

The design of large catamaran sailing yachts requires balancing aesthetics, comfort, and performance, with wet deck geometry having a strong influence on resistance, motions, seakeeping, and slamming. This study introduces a method to characterize wet deck geometry by parameterization of key geometric variables suitable for early stage design, and examining its impact on operability, which is a primary factor influencing passenger comfort. In the study, four non-dimensional geometric parameters, namely non-dimensional wet deck height (h/L, where L is the vessel length), non-dimensional hull separation (s/L), demihull beam-to-draft ratio (b/T ), and non-dimensional longitudinal starting position of the wet deck (Lswd/L) were varied systematically across three different vessel lengths, producing 885 design configurations. The performance of these designs was quantified using the Comfort Operability Index (cOI), defined as the percentage of time a vessel remains within predefined comfort limits. Similarly, four seakeeping criteria, including effective gravity angle (EGA), motion sickness index (MSI), vertical and lateral accelerations, and slamming probability across multiple onboard locations, were evaluated using response amplitude operator (H(ω)) values for various design configurations. The H(ω) were generated using Maxsurf Motions and an engineering correction was applied to the heave response in beam seas. The analysis covered three headings, and two operational geographical areas representative of the Mediterranean and the Atlantic Ocean. Results indicated that increasing vessel length consistently improved cOI, particularly in head and bow quartering seas. Among wet deck parameters, s/L showed strong influence on lateral acceleration and EGA in beam seas, while b/T and Lswd/L significantly influenced MSI and vertical accelerations in head and bow quartering conditions. The method provides valuable early-stage insight into wet deck design, with future work recommended to incorporate sail-induced loads. Keywords early-stage design; sailing catamarans; comfort operability; strip theory; seakeeping; wet deck; multivariate fractional polynomial