ABSTRACT
Propulsion Improving Devices (PID) aim either at improving the wake distribution, or at recovering rotational energy from the water behind the propeller and converting it into thrust.
In the first group, for slow ships, the wake equalizing ducts and the Mewis duct provide savings in the range of 3-8%. Similar to the ducts, the pre-swirl stators improve the overall efficiency by about 4% on the VLCCs where they are installed. While increasing the resistance, the improvement in wake leads to an increase in efficiency. For faster ships, ducts are not useable, and other devices (e.g. turbulence stimulators) are used. The second group consists of, for instance, Propeller Boss Cap Fins (PBCF), which provide savings of 3 to 5% ( Hollenbach & Reinholz, 2011).
