"claus" wrote
The (folding) prop on our boat is made of Bronze.

Are you trying to protect the prop or are you trying to protect something
else from being corroded by the prop? Bronze is way up on the cathodic end
of the galvanic scale, meaning it *should* corrode zinc fairly rapidly. And
of course it will also corrode other anodic metals like aluminum or iron if
there's no zinc handy. What other metals are involved? Is there a problem
other than the prop zincs eroding?