In some cases, many have seen the red or "pinkish" propeller look or have seen some excessive pitting, often caused by cavitiation, or even wonder when the last time the zincs were replace.
Galvanic Action is the most common cause of corrosion on boat propellers, because saltwater is in itself the electrolyte needed to complete the process.
One of the best ways to prevent this is to ensure your zincs are replaced before they are worn, doing so after the fact allows the propellers to begin sacraficing their metals. Electrolysis, what we often think of, occurs rapidly and is most often caused by stray current coming from the shoreline, dock power or other boats. Bronze is also subject to the same conditions due to the zinc being leached from the material.
Stainless is generally less impacted, however does corrode freely and quickly in small areas and is generally called crevice corrosion.