Came across some funny stuff going on with an iron keel in a marina once. It seems that electrical (mis)wiring in a neighboring boat caused an accretion of iron "filings" on the exterior of a cast iron keel on the side nearest the electrical current. This was happening through the paint. Upon hauling for inspection, the keel was covered with "droplets" that looked like leeches, which when touched (and the surface tension broken) broke open into powdery rusted dust that fell to the ground. Scary. Don''t think this would happen with lead, or in a marina with better wiring, but it''s something to be aware of.