SACRIFICIAL ANODES
Zinc anodes or also known as zincs or sacrificial anodes protect any part of the boat that is subject to galvanic corrosion. Galvanic corrosion can occur whenever two or more dissimilar metals that touch each other are immersed in any liquid that can transfer electricity. For example: water, saltwater, freshwater with high mineral content, and polluted freshwater are very conductive, and the conductivity goes up with water temperature. The two metals become a battery, so there is current flowing between them. The electrons that make up that current are supplied by one of the metals. This metal is giving up bits of itself to the seawater and obviously, this process rapidly destroys the metals that are underwater. Galvanic corrosion can be prevented by adding a third metal to the circuit. This metal is zinc, because it oxidizes more easily than iron, therefore it corrodes first. When the zinc anode, or sacrificial anode is mostly consumed, it can simply be replaced. Many professionals consider that the best sacrificial anodes are made from an activated alloy in which catalysts have been added to ensure that the sacrificial anodes give 100% of themselves in the purpose of protecting your boat from corrosive action. Fortunately sacrificial anodes are relatively inexpensive and are readily available. Sacrificial anodes can waste away at an accelerated rate due to warm water temperatures, polluted water and stray current corrosion. That is why it is essential to check them on a regular basis. The parts of the boat that are at risk are a bronze or aluminum propeller on a stainless steel shaft, metal struts, rudders, rudder fittings, outboards, and stern drives. It is a good idea to use 1% of the surface area of the protected metal to start. Check the protected metal frequently. You will know that it needs more surface area if it begins to show signs of corrosion. It is important to replace the sacrificial anodes when they have lost half their weight. For example, if the new sacrificial anodes weigh 10 pounds, it is a good idea to replace them when they weigh 5 pounds. When a sacrificial anode lasts less than a year that means that you might need another one with more weight. For sacrificial anodes to provide any protection, they must be in electrical contact with the metal being protected. A circuit must be completed for the sacrificial anode to be effective. This is why a hanging grouper-style of anode comes with a wire and metal clip that is intended for attachment to a "ground" within your boat. The electrical contact has to be very good, so the sacrificial anodes need to be bare and bright before they are installed. Never paint over sacrificial anodes with bottom paint, which will only isolate and protect the anodes from their intended purpose and make them useless. It is very important to determine which sacrificial anodes will fully and safely protect a boat. It is also essential to understand how the sacrificial anodes work with different hull compositions, stern drives, and types of water. Use zinc alloy anodes only in salt water. Many professionals donÕt recommend them for use in fresh water. The aluminum alloy sacrificial anodes should be used in salt or brackish water. They are not recommended to be used in fresh water, and they last longer than zinc. The magnesium alloy sacrificial anodes are to be used in fresh water only. They are not recommended for use in salt or brackish water since the result may be an accelerated corrosion rate. This may leave you with no anode protection in a short period of time and damage the metal parts of your boat.