Anodes - Protecting your boat -Welcome
Welcome to our information page on choosing, fitting & understanding anodes for your boat. Below is some helpful advice on what protection the anodes offer and common problems and misconceptions experienced.
We stock one of the most comprehensive range of anodes you will find in the UK, from MG DUFF to Genuine Honda, Yanmar and others. If you want to look through our selection of anodes from the catalogue, please select the relevant link below.
Anode Range
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Anodes -Why Do we need them?
Essentially, when you submerse metallic items in any kind of water or conductive medium for any period of time, galvanic corrosion will occur due to differences in the potential (charge) on the metals. The amount of corrosion will depend on many factors, including the type of metal, conductivity of the water, surrounding electrical activity, and the bonding and type of metals which are in contact with the water.
To reduce or negate the effect of this corrosion, boat owners fit sacrificial "anodes" to their craft, which effectively concentrate the galvanic corrosion onto these anodes by offering these destructive galvanic currents a more favoured target. When bonded with a metal with less favourable galvanic properties (or a lower cathodic index), the anodes (which have a higher cathodic index) will naturally create a more favourable electrical potential and therefore protect the more valuable metal parts (propellers, stern drives and the like). This property is even true when considering the application of paint & antifouling, as copper-based antifoul, if applied directly to a metal substrate, may cause similar problems.
Click here to see the range of Anodes available
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Protecting your boat
It is obvious that the rate of decay of anodes will vary considerably, and even from boat to boat in the same area. It is therefore essential that you check the decay ("wear") on the anodes periodically, and ensure that there is no possibility of them "wearing out" and offering no protection. A yearly inspection is advised, though if problems have been experienced in the past, more frequent checks may be necessary. If checking when the boat is lifted out for annual maintenance,, if any specific anode has more than 60% wear, it is normal to have it replaced, considering that it will probably be as long again before the next opportunity.
It is important to realise that the effectiveness of the sacrificial anode will depend on how well it is bonded to the material it is protecting. This is true in the case of fitting shaft anodes, where the surface area of contact between the anode and the shaft may be small in comparison to the surface area of metal being protected. Be aware also that loose or badly fitted anodes will have a reduced capacity for protection, and that you should never paint over an anode or in between the contact surfaces where it is fitted.
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Types of anode - Zinc, Alumimium and Magnesium
Anodes are manufactured from 3 different types of metal - Zinc, Aluminium & Magnesium. These metals are chosen for their cathodic index and also for their other properties that make them suitable. The metal chosen for your particular protection will depend on where the boat is situated and its area of use. As a general guide:
Salt Water - Zinc or Aluminium
Brackish Water - Aluminium
Fresh Water - Magnesium
It is vital that you choose the correct type of anode as if used in an environment outside that stated, the ability of the anode to work will almost certainly be compromised. If you are likely to use your boat in waters other than those for which the current fitted anodic protection is designed for more than a few days (2 weeks maximum), you should consider fitting the correct type of anode or the water s you are visiting.
Zinc and Aluminium anodes, whilst in fresh water, will develop a white oxidisation, which will effectively prevent the anode from operating. Similarly, magnesium anodes are more reactive than Zinc/Aluminium and when used in Salt/Brackish waters will decay far more rapidly and often cause deposits on other protected surfaces.
Click here for our range of Zinc anodes (saltwater)
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Common anodes
Most craft are protected by a standard set of anodes - namely the ones you find on the shelf in most chandlers. The availability of such anodes is normally good and the range offers solutions to most manufacturers/owners needs.
Many engine manufacturers have specifically designed anodes for their engines and drive systems, but in most cases these are common parts that can be ordered or are in stock. Certainly, the range of hull anodes has been well defined over the years and a variety of manufacturers produce very similar weight/design anodes, albeit with some offering more hydrodynamic shapes and better structure. They are all designed to fit/replace their counterparts and they are generally compatible with each other - as long as you ensure you keep the same type of metal for the anode - using a mixture of, say, Zinc and Aluminium anodes on a single boat would offer only a fraction of the required protection.
Generally speaking, anodes fall into one of the following categories:
- Engine/Out drive anodes - specially designed anodes for particular models.
- Stern gear anodes - Shaft and Prop nut anodes matched to the diameter of your prop shaft.
- Hull anodes - A range of anodes of specific length/weight etc. that are either welded or bolted to the hull.
- Bow thruster/Trim Tab anodes - specialist anodes for specific protection of these parts.
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Tips on fitting anodes
As said above, an anode will only be effective if it is bonded to the part it is protecting and its surface is free from contaminants. Make sure that your anode is "clean" - i.e. it is not covered by paint or any other substance that will prevent the bare metal being exposed. If your boat is out of the water and the anodes have sufficient wear left in them, then at the very least give them a clean with a wire brush to ensure that fresh metal is exposed.
If you are replacing your anodes, ensure that the anodes you fit are suitable and check for any issues that would indicate problems. If any issues are apparent (pitting of propellers etc.) then decide whether your current protection is working adequately - it may be that anodes have become displaced or worn, or possibly not correctly fitted. If in any doubt, check with a professional to advice on what you need to do/change to protect your craft.
When re-fitting anodes, always take time to prepare the bonding surface that the anode attaches to which will ensure clean bonding - these areas often suffer from build up of debris etc.. Leisure anodes are more often than not attached by use of bolts to the Hull/Drive leg etc. Some anodes have integral plates which ensure that even when worn, the anode is still securely attached to the craft. Anodes that are internally bonded using wires to their respective part must be checked to ensure that the bonding cables and fixings are not corroded or loose.
The use of a thread locking compound is commonplace when attaching anodes with bolts as this helps prevent loosening and subsequent loss of the anode, Make sure that the compound does not interfere with the attachment of the anodes to the surface it is protecting. (PJ)
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![Tips on fitting anodes]()
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