When two dissimilar metals are electrically connected and submerged in a solution or electrolyte a natural chemical reaction takes place. This chemical reaction forms a circuit where the least noble metal (the anode) will begin to break down leaving the most noble metal (the cathode) intact. For example, a sailboat may have many metals electrically connect in salt-water solution. The stainless steel propeller shaft is more active (least noble) than the bronze propeller. In this case the stainless steel propeller shaft will naturally begin to breakdown leaving the propeller intact. Since propeller shafts are expensive to replace it is easy to protect these metals by adding a zinc collar anode to the shaft. The anode is highly active and will corrode instead of the other metals it is electrically connected to.