A catamaran having two parallel symmetrical hulls of equal size spaced apart with a superstructure lower deck extending from an outer edge of the first hull to an outer edge of the second hull. The lower deck is positioned above the static waterline and provides a single, constant, flush elevation height across the entire length and breadth of the vessel, with the placement of control and propulsion machinery in the hulls. The improved catamaran has an increased freeboard, increased gross tonnage, and decreased design pressures on the superstructure scantlings of the catamaran deck as compared to a conventional catamaran having a lower deck mounted beneath the static waterline, or accommodations added to the hulls.