Hydrodynamic analysis of a catamaran derived from a Fridsma planing hull: Effects of demi-hull spacing, wake dynamics, and resistance

Using single-hull models as baseline for catamaran design is fundamental for accurate hydrodynamic analysis and vessel optimization. In this study, STAR-CCM+ software with K-Epsilon turbulence model is utilized to numerically analyze hydrodynamic performance of a catamaran composed of two Fridsma hulls at various spacings. Three configurations (cases A, B, and C, corresponding to S/L = 0.05, 0.10, 0.15, respectively, where S represents hull spacing and L is the vessel's length) were evaluated at four velocities (2, 4, 6, and 8 m/s) corresponding to longitudinal Froude numbers (Fr) = 0.4, 0.8, 1.2, and 1.6, focusing on wake formation, total resistance, trim, and heave. Findings reveal that hull spacing has significant impact on hydrodynamic behavior. Case A demonstrated the best performance at low Fr (62.7 N resistance, Fr = 0.8), while Case B performed optimally at moderate Fr (78.74N, Fr = 1.2). Case C yielded the lowest resistance at high speeds (97N, Fr = 1.6) and exhibited enhanced stability under high-Fr conditions. Wake analysis at point y0 (centerline at tunnel exit near the stern) revealed that increased Fr and reduced trim result in longer rooster tail wavelengths and lower amplitudes. Although hull spacing produced a similar trend, its influence was comparatively moderate. At point y1 (transverse center of the demi-hull stern), changes in rooster tail shape were minimal prior to planing and became negligible once planing occurred, particularly in Cases B and C. Further analysis of transverse wake patterns confirmed that increasing spacing reduces interference effects. Case C showed the least flow interference, while Case B offered well-balanced solution between reduced interference and favorable design constraints such as length-to-beam ratio.