That's my understanding. But the collapsing bubbles are next to the cartilage I believe, and it seems to me should therefore be causing cavitation erosion. W

That's my understanding. But the collapsing bubbles are next to the cartilage I believe, and it seems to me should therefore be causing cavitation erosion. When cavitation erodes a boat's propeller, the cavitation is occurring in the water next to the propeller, not in the propeller itself. https://en.wikipedia.org/wiki/Cavitation#Cavitation_damage https://en.wikipedia.org/wiki/Cavitation#Cavitation_damage