Zincs & Dissimilar Metals

Some ocean water (electrolyte), a zinc, some graphite impregnated packing and a silver/silver chloride reference cell..

[@OuterValence]

Good demo.
You could demo a Galvanic Isolator with the same setup to see the effect on current in a shore power scenario. Perhaps demo the change in Anode/Cathode surface area ratio. Reason for painting a large bronze prop on an aluminum hull fishing vessel.