Delayed sheet cavitation inception has occasionally been observed in the MARIN Depressurized Towing Tank (DTT). The problems are specifically related to the pressure side of model ship propellers, and occur despite the application of leading-edge roughness. As a consequence, no cavitation at all or cavitation on parts of the propeller blades is observed, in cases where cavitation in the cavitation tunnel or at full scale is present. In an exploratory investigation, the effect of several parameters that may influence cavitation inception is studied in the DTT. In particular, the influences of Reynolds number, free-stream turbulence and additional gas nuclei are investigated. It is concluded that the presence of sufficient gas nuclei is crucial for sheet cavitation inception, even if leading-edge roughness is applied. With additional nuclei in the propeller inflow, sheet cavitation inception in the DTT is no longer delayed with respect to the cavitation tunnel.

Cavitation nuclei are added to the flow to achieve adequate scaling of cavitation phenomena in model-scale facilities with respect to full-scale conditions. During propeller cavitation studies in MARIN's Depressurized Wave Basin (DWB), cavitation nuclei are added to the flow using electrolysis. In the present study, Interferometric Particle Imaging (IPI) was applied to determine the size and the concentration of nuclei in the wake of a ship model. The dependence of the nuclei size and concentration spectra on the electrolysis current and the basin pressure showed good agreement with theory. One limitation of the present technique was identified: the minimum size of nuclei that can be resolved is approximately 40 µm. This also limits the basin pressure at which nuclei measurements can be performed to a maximum of approximately 100 mbar.