To decrease the wave making resistance of a high-speed catamaran at the front hulls with the relation with the ship speed taken into consideration and avoid slim construction of the ship by defining the lower limit.

A catamaran ship having a displacement of 150 ton or more has such a space that water stream flows back between the hulls (a) with the advance of the ship and part of the upper part of water stream contacts with the atmospheric pressure at all times, wherein the outer side faces (b) of the ship are made approximately parallel in the advancing direction of the ship, and the angle θ of a forward thinning wedge form of each front hull leading to the front extremity should range between 5 and 15 degs.