Cavitation
Cavitation is a hydrodynamic phenomenon where vapour bubbles are generated and collapse on a surface when the fluid is subjected to a drop in pressure. In the case of a boat hull, hydrofoil, propeller or marine turbine blade this phenomenon will occur when speeds near or surpass 15m/s (30knots). In the propeller industry high strength metals are used to survive the effects of cavitation. In some cases, propellers have been replaced due to holes being worn straight through them. The entire marine turbine will not experience this speed; however blades tips can easily reach these speeds if the designer is not careful. To test blade materials and coatings for cavitation a designer is recommended to use the ASTM G32 process.
http://eprints.soton.ac.uk/43767/1/our_anti-fouling.pdf
