Seawater has corrosive properties that are even more problematic when it contacts items containing two different metals. One of the metals will release electrons in the presence of seawater creating a current between the two metals, which acts like a battery. The process, called galvanic corrosion, is something that all boat owners should be aware of so they can do what they can to prevent it from damaging the vessel. The most effective way to deal with this problem is to introduce a type of metal that releases electrons more readily than the metals used to build the boat. Zinc is the most popular metal for this application and in the boating industry, the piece used is called a zinc anode.
Anodes should be in place in any location where two metals contact each other and are vulnerable to galvanic corrosion. One common area for this treatment is where the aluminum propeller attaches to the stainless steel shaft but there are other locations featuring two metals in contact with each other. The zinc anode provides protection against corrosion and saves the boat owner from costly repairs and the need to replace corroded components.
Some individuals mistakenly believe that zinc in any location will offer protection for all other metal parts on the boat. The zinc anode will not protect metal unless it is direct contact with it. This is not a problem for boat owners because engine and boat builders design parts to accommodate zinc anodes in many locations where galvanic corrosion can be an issue whether they are zinc hull plates for protection of bronze fittings, zinc collars that fit around the shaft or various engine parts.
Once you understand the importance of placing zinc anodes, you should be aware that these pieces are under stress and will not last forever. The piece is sacrificing itself to offer protection for important metal parts that ensure the boat’s integrity and this means they are wearing down as they corrode. In general, most boat owners will replace them once per year making sure they occupy approximately 1% of surface area in the region they are protecting. Even with zinc anodes in place, you should regularly inspect all metal parts for corrosion and if you notice any problem areas, you need to replace the zinc anodes as soon as possible. Most people replace the zincs when they are half consumed. Beyond that, the pieces are not able to protect parts from corrosion effectively.
Boat owners will find that zinc anodes are affordable and cost from several dollars for a small piece to large hull plates for less than $30. Installation requires the anode be in direct contact with metal and users should avoid painting the zinc and make sure all surfaces are bright and bare before placing the anode. Before replacing any anodes in the engine compartment, you should read the owner’s manual that came with your boat so you can locate all the zincs, even the ones in hard to see areas to make sure you do not miss any.
Installing zinc anodes is an effective way to protect metal boat parts but you must ensure the anodes are still doing the job because they will only offer adequate protection against corrosion if they are less than half depleted. You can avoid any big corrosion problems if you inspect all metal parts regularly and always replace any zinc anodes when they are more than half depleted. If you find that you are having to replace your zinc anodes more frequently than once per year, you should purchase and install larger zincs for longer performance.