In the hostile and highly corrosive marine environment, advanced composite materials can be used in marine current turbines due to their high strength-to-weight ratios and excellent resistance to corrosion. A composite material marine current turbine (CMMCT), which has significant advantages over traditional designs, has been developed and investigated numerically. A substantial improvement in turbine performance is achieved by placement of a duct to concentrate the energy. Computational fluid dynamics (CFD) results show that the extracted power of a ducted CMMCT can be three to four times the power extracted by a bare turbine of the same turbine area. The results provide an insight into the hydrodynamic design and operation of a CMMCT used to shorten the design period and improve technical performance.