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Zinc vs. Aluminium Anodes
Author: Stuart Buckingham Date Posted:20 October 2017
Anodes, for those who may not know, are the bare metal looking objects bolted in various positions on your outboard. The most obvious ones are the trim tab anode above your propeller, the square block anode above your cavitation plate and/or the bar anode under your trim and tilt unit.
All anodes, depending on the outboard make, can be different shapes and sizes and made of different materials depending on the environment they’re being used in. Below I'll be covering the two main types of anodes, Zinc and Aluminium, and the environments that suit them best.
Zinc Anodes have, for many years, been the go-to anode for boaties. Zinc is a less active metal and therefore last longer in the marine environment. However, zinc anodes are realistically only good in saltwater. When used in fresh water for extended periods zinc anodes can produce a zinc hydroxide layer rendering them useless. So, if your anodes have been on your engine for a number of years, and still look like new, then it's worth pulling them off and replacing them. Zinc anodes are generally quite heavy as opposed to aluminium anodes which are typically much lighter.
Aluminium anodes, in my opinion, are the best anode for all environments. Aluminium is a more active metal than zinc in saltwater and are also well suited to freshwater applications. In fact, Mercury Marine uses aluminium anodes almost exclusively on their outboards. I’ve been asked the question many times over the years; "my boat and outboard are aluminium, why does the anode corrode and not them?". The simple answer is that there are different types of aluminium, and the aluminium manufactured to produce anodes is different to the marine grade aluminium used in your boat and outboard.
So, the next time you're servicing your outboard remove your anodes and have a good look at them. If in doubt, replace them with some aluminium anodes (where possible) and you'll be giving your outboard the best protection possible against corrosion.
Aluminium anodes22 October 2017Makes a lot of sense,do you stock them for a 6hp two stroke Yamaha,if so can you sell me one,l have purchased an impeller for a 15 hp Yamaha previously
Outboard Spares Response
Hi Tony, unfortunately, we don't have any anodes for those smaller engines. We have a few internal anodes but they only suit the four stroke engines. Sorry, we couldn't help with this one.