Author: Boat Accessories Australia Date Posted: 29 May 2017
Checking and replacing your boat’s anodes is an ideal task for the winter months. Maintaining them regularly like this will save you from replacing expensive parts or treating the whole boat for corrosion-related damage if left too late. All boats are susceptible to corrosion but they are more at risk the more time spent in the water. Boats penned in a marina are particularly vulnerable as being surrounded by other boats and the dock can contribute to their corrosion. For more information on this, check out our other article on corrosion in the marine environment.
If you want to protect the metal on your boat you need another metal that is more active (i.e. corrodes faster) than it. The most active metal becomes the anode that will corrode instead of the other metal, thereby providing cathode protection. Corrosion of the anode means it becomes ‘sacrificial’.
Three of the most common metals used for anodes are magnesium, zinc and aluminium. Magnesium has a lower current capacity so it corrodes quicker and only lasts a third of the time of a zinc anode. Zinc is the most common material used and great for the majority of salt or brackish waters in Australia. Aluminium has a higher electrical capacity than both and is also significantly lighter so it not only lasts longer but won’t add as much extra weight to the boat which results in better fuel economy. It is also extremely versatile and is ideal for almost all boat and water types (more on this later). Boat Accessories Australia stock a wide range of different zinc and alloy anode parts.
If your sacrificial anode is doing its job properly, it will corrode and eventually become inactive. It can be hard to tell when the anode has stopped working (unless your other metals start to show signs of corrosion) however there are many available with indicators that appear once a certain layer of metal has corroded away. You should change your anode at least every 12 months or when it has corroded to half its original size to ensure it is working to its optimum level. Make sure during installation there is no paint on the metal surface that is in contact with the anode and remember not to apply any paint or other products to anodes to ensure good electrical contact.
Corrosion rates can increase depending on the saltiness and temperature of the water. The higher the salt content and the higher the temperature, the more corrosion will occur. In fact, corrosion doubles with every ten degrees the temperature rises. Other factors involved in increasing corrosion include pollution in the water, lack of oxygen for metal (covered up by barnacles or bolts) and the existence of certain types of bio-organisms.
The right anode depends on the type of water where your boat spends most of its time. The anode metal recommended for all water types is aluminium. Zinc or aluminium are best in salt water, magnesium for fresh water while aluminium or zinc can be used in brackish water.
Zinc anodes contain traces of Cadmium, a highly toxic and bioaccumulating metal for aquatic life so if you’re environmentally-minded, aluminium anodes are a much greener option for the marine environment.
Not all metal parts of your boat are protected by the anode. Your trailer springs, axles, brakes and wheel bearings are still at risk of corrosion. It is best to wash them down after using so corrosive salts can’t penetrate the metal. It’s also handy to use Bel-Ray products for certain trailer parts like Waterproof Marine Grease on the bearings and Rust Preventative Coating on the springs and axles.
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