A marine vessel corrosion control system contemplates redundant protection for a marine vessel against the effects of galvanic corrosion. The vessel is equipped with typical zinc anodes interconnected together and attached to metallic components to be protected from galvanic corrosion. A reference electrode immersed in the water provides signals to a control box representative of electrode voltage as compared to an internal stabilized voltage standard. The control box compares the reference electrode voltage with the internal stabilized voltage standard and feeds current through a hull mounted anode into the water and through the submerged metal parts of the vessel. A relay allows selective interruption of the connection between the passive zincs and the vessel ground and selective closing of that circuit. The relay is connected to the control box and when the control box fails in any way, this failure is sensed and results in deactivation of the normally closed relay to electrically interconnect the passive zincs to the vessel ground until the active galvanic corrosion control system is repaired.