Directed energy deposition (DED) processes have a great potential for ship building industry to reduce the lead time of ship part supply. However, ship parts such as propellers and impellers have critical requirements on material's properties and component's performance. To ensure the exploitation of DED manufacturing for critical parts, an optimization approach of DED process was developed and demonstrated on waterjet impeller made of duplex stainless steel. The developed approach is based on the understanding of the effects of DED process and heat treatment on the material microstructure, and the effects of the microstructure on the material properties, all optimized to fulfil the requirements on the component. The manufacturing and qualification testing were planned based on the requirements in accordance with the current standard guidance. The assessments by standard testing methods, including tensile, Charpy impact, and bending tests demonstrates that the DED material with an optimized heat treatment fulfil the standard requirements. Corrosion and cavitation tests were also performed and demonstrates the high resistances of DED material to cavitation erosion.