Rick, understood and agreed. Indeed, metallurgy and corrosion is a field not well understood by most folks in this industry, and frustratingly they too often don't learn from their mistakes. In fact, corrosion is the area where there is by far, in my experience, the greatest degree of misunderstanding among professionals, it isn't intuitive, it requires education to understand and diagnose. But, most simply guess.
Hard to find is an understatement, there really is no such thing as a bronze propeller in the true sense of the word, nearly all are "manganese bronze" (as are "bronze" prop nuts) which is, because of its zinc content, actually brass. Nickle-Aluminum-Bronze or NiBrAl, is an option that has greater corrosion resistance and tensile strength, however, it more costly, less common. Because most props are manganese bronze/brass, they absolutely require cathodic protection, i.e., zinc protection.
Interestingly, that broken minesweeper (or was it a YP?) bolt doesn't look dezincified, were there signs of pink?