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Boat owners and boatbuilders across the UK are being urged to switch from zinc to aluminium anodes to help marine life, in addition to the scientific and price benefits.
The call for an industrystandard change follows research by the Clean Harbours Partnership (CHP), and is supported by PBO’s expert metallurgist Vyv Cox.
Boat anodes protect underwater metals from galvanic corrosion. If you have two dissimilar metals, the water will act as an electrolyte and the less noble, more reactive of the two will corrode instead of more valuable boat parts.
Sacrificial anodes are usually aluminium, zinc or magnesium.
The CHP has been looking at the release of copper and zinc by recreational vessels into the marine environment, and is now advocating an industry change because zinc anodes contain cadmium, which is particularly harmful to marine life.
In 2020, Professor of Marine Zoology at the University of Portsmouth, Gordon Watson, calculated that 900 tonnes* of zinc is released annually into UK coastal and inland waters by recreational vessels.
“The problem is metals do not degrade. They accumulate in the ocean and in sediment on the sea bed, where organisms at all levels in the food chain ingest them. Zinc anodes also contain cadmium, which is harmful to marine life, whereas aluminium does not,” said CHP advisor James Collings-Wells. “While aluminium anodes are being used by some of the UK’s major boat manufacturers, they are not used widely enough.”
Boaters should also consider the amount of anodes required. Professor Watson added: “We think that many boaters have too much –aluminium or zinc.”
Zinc versus aluminium
Metallurgy expert Vyv Cox, the author of Metals in Boats, said zinc anodes were previously favoured because aluminium alloy anodes were for many years much more expensive, limiting their application. The cost of high purity zinc has doubled in the past 10 years according to manufacturer MGDUFF, meaning aluminium anodes are now the cheaper option. Less research has been done on it but aluminium alloy is believed to be more environmentally-friendly, it is lighter, and has several performance benefits. Vyv said: “While the galvanic potentials of zinc and aluminium anodes are very similar, aluminium anodes are superseding zinc ones in general use as: they may be used in
