The “design spiral” of a new ship consists of various milestones, one of them dealing with resistance prediction of the fully appended hull and with the proper placement of appendages, especially in the stern part of the ship where a complex 3D flow grows up. Applying an open-source code, the Open-Source Field Operation And Manipulation (OpenFOAM) one, in this paper it’ll be shown a fast numerical, robust and user-friendly procedure for the designers to achieve struts proper alignment rather than rely on a traditional more expensive, both in time and costs, Experimental Fluid Dynamics test campaign. An open-access data of a twin-screw propellers ship, the David Taylor Model Basin (DTMB) 5415, has been here considered to carry out the Fast Procedure. Once the test case has got through the Verification and Validation procedure, different kinds of simulations have been performed to assess that a Double Model simulation with the effects of trim, sinkage and propellers can describe with an adequate degree of accuracy the orientation of the field. It has been possible to carry out this last assessment through the generation of a cloud of points next to the struts position to obtain the orientation of the field and evaluate the difference between simulations. Two substantially hydro-dynamically equivalent approaches have been considered to design new struts in order to minimize their interactions with the hull and other appendages. Through the use of this Fast Procedure, the design time is evaluated equally to a few days, and it can be performed without specific knowledge or huge computational resources and so it can be considered industrially affordable.