Zincs protect your running from galvanic corrosion. Galvanic corrosion occurs from dissimilar Alloys being in an electrolyte such as seawater. Zincs are a type of Anode, other types of Anodes include Aluminum and Magnesium. You might ask yourself which type of Anode should i be using on my boat! Zinc and Aluminum Anodes are used in saltwater while Magnesium Anodes are best suited for freshwater.