In the transition to a carbon neutral future the reduction of $CO_2$-emissions within the shipping industry is important as this industry accounts for $\approx$3 \%. One such way is though energy saving devices such as the propeller boss cap fins (PBCF), which in this report is numerically investigated with RANS simulations in open water and rudder conditions. The Q-criterion was used to visualise the PBCF' effect on the hub vortex.
A parametric model-scale study with the four PBCF parameters, chord length, height, pitch and rake was conducted based on a validated, grid independent simulation, which resulted in an 0.76 p.p. open water efficiency gain for the best case with a chord length of $9\%$ propeller diameter.
The best case PBCF was used to explore the correlation with a controllable pitch propeller, that found gain in efficiency for a pitch-diameter ratio above 0.9.
The best case PBCF was also used for exploring the scaling effects between model- and full-scale simulations, which found a 1.71 p.p. gain in comparison with the model-scale simulation with an inclusion of the same PBCF.