A Research and Development of PBCF (Propeller Boss Cap Fins)

PBCF (Propeller Boss Cap Fins) was devised to enhance the efficiency of a ship's screw propeller by reducing the energy loss due to the propeller hub vortex and this was proposed in the paper presented to the Journal of the Society of Naval Architects of Japan, Vol. 163 (1988). The concept of PBCF is that the same number of small fins as that of the propeller blades are attached to the boss cap (hub cone) and that they rotate together with the propeller blades. The hub vortex is considerably weakened and the kinetic energy from the rotating flow around the boss cap is recovered by the fins and accordingly the propeller efficiency is significantly increased.Following the previous PBCF paper, research into the PBCF effect was carried out through the measurement of the flow behind the propeller by 3D-LDV, the force measurement of PBCF and the cavitation test in a propeller slipstream. The following points were clarified from the results of experiments : …Decrease of rotational flow velocities and acceleration of the flow of fore and aft direction behind the PBCF are confirmed quantitatively.…PBCF generates torque reduction and also makes a main propeller increase thrust.…The hub Vortex cavitation is eliminated by PBCF.As for the PBCF effect on actual ships, 4.3 % of the efficiency gains on average from the analysis of the data from eleven sea trials of various kinds of ships, and a significant efficiency gain from the analysis of actual voyage data were obtained. The certain scale effect between the model and the actual ship is considered to explain the difference in the efficiency gain.These results lead us to believe that PBCF is an excellent and practical energy-saving device because of its simple concept and the reliable efficiency gain of about 4 %.