This master's degree thesis aims at the fluid-dynamic study of the hull of a boat that performs the function of water-bus within the Venice lagoon. In particular, it turns its attention to the optimization of the shape of the immense part of the hull of a SWATH, a particular type of boat which has already been used for some time as passenger ships and fast ferries. Small Waterplane Area Twin Hull (SWATH) vessels are buoyantly supported vehicles with most of the buoyancy provided by twin hulls below the water surface in torpedo-like shape. One or two slender surface piercing struts per side connect each of these hulls to the cross-structure located well above the water surface.