Ok guys,

A bronze prop YES.

 nothing special about that.

 BUT the only way I can explain it is!  it looks like growth but it wipes off.

 if left in the same position for a long period it looks like tears of rust running down the blades.

I have seen this once on a 1950 sailing boat and this was really bad the prop was knackered.

The reason I ask is I fitted a new prop 8weeks ago went in today and these small bubbles of ??? are all over the blades and boss yes ok it wiped off, but??

So ok it is some form of corrosion / oxidation/ electrolysis but does it have a proper name i am sure this sort of problem must have ??.