This paper considers the design of a low-cost and modular unmanned surface vehicle (USV) used for marine environment monitoring or survey. The hull chosen is a catamaran type since it improves stability against waves, and the shape of ship is exploited to reduce the resistance. The mechanical design is based on a two-hull construction because of its low risk of capsizing in rough water. In order to satisfy requirements of USV mission, it should have acceptable speed, endurance, maneuverability and stability under inappropriate conditions; furthermore, enough payload capacity. The computational fluid dynamics (CFD) and max surf modules are used to predict calm water resistance for the floating hull through calculations. To design the floating hull and estimating the hydrodynamics performance of it, calculations are carried out using three different mesh sizes in the range of 0.7 to 0.3. The fine grid gives most appropriate results because convergent results are obtained as the mesh size decreased. Using the designed model, a prototype of unmanned surface vehicles (USVs) was developed. The prototype will be tested to prove that.