Apparatus for minimizing galvanic deterioration of the metallic hull of a ship moored at a dock of a dissimilar metal, and receiving electrical power from a power source grounded at the dock, includes a plurality of silicon diodes connected to an electrical power conductor grounded at the dock and at the metallic hull of the ship. The intrinsic junction voltage drop of the diodes is sufficient to block current flow due to the voltaic cell effect between the ship''s hull and dock.