Hydrodynamic performance comparison between twin hulls

When designing a twin hull, resistance and seakeeping are operative requirements which often clash each other. It very well known that SWATH hulls, having classical lines, display good seakeeping features, but bad resistance performance. Conversely catamaran hulls, when appropriately designed, display satisfactory resistance features, but the seakeeping qualities are less satisfactory, unless additional submerged flaps are fitted. To improve the SWATH resistance of a new design hull, the lower hulls and the struts geometry were optimised at INSEAN research centre in Rome, by using numerical methods, obtaining a more slender and faired configuration. This new geometry significantly modifies the general features of a classical SWATH hull, converting it to a MWATH hull, the resistance characteristics of which was optimised. The resistance, trim and sinkage and the wave pattern resistance were measured and compared for two models, a catamaran and a MWATH, having the same length, width and demihull distances; the most appropriate speed intervals were defined for every tested condition. This investigation also permits defining the most suitable operative configuration for a specific design by using these hulls.