Agitation, no cavitation.
Maybe you have been walking along the beach in Aquatic Park and noticed two huge propellers sitting in the sand near the east roundhouse. I've been walking by those for years and decided to do some investigating.
According to a reliable source, a fellow who has worked at the park since he was 16 years old, and I won't mention his current age, told me the propellers are from the double-ended ferry Klamath and have probably been out there in the park since the late 1960s. (More about the Klamath in a moment.)
What is cavitation and how can it pulverize steel? This phenomenon can occur under certain conditions during the rotation of a screw propeller. In the turbulent water around the propeller air bubbles can't escape so they implode, releasing energy, and causing physical damage to parts of the prop.
See you in the park and try not to trip over those props!
Park Ranger Christine