Technical Information

The problems start when, like most people, you move between the environs. If you use magnesium anodes in brackish or salt waters, they will be eaten away very quickly. Conversely, if you use zinc in freshwater or low salt estuaries, they will oxidise and become blinded. Aluminium will also become ineffective in a freshwater lake.

If you are going to transfer your boat to a different water type for more than a few weeks, it is advisable to change your anodes for the correct type. If you are daily moving between the zones, just choose your anodes for the major usage, and then keep a constant check on them to make sure they are being corroded and not being covered in a white crust.

The chances are that you are replacing anodes that have already been fitted and, therefore, it is just a matter of replacing like with like.

All anodes should be positioned as close to, and in line of sight of the part they are designed to protect. They must be electrically bonded to the protected part with 4mm2 multi-stranded cable.

A] Rudders – various sizes and weights of round disc anodes, some of which are through-bolting pairs available to mount to the rudder below the waterline.

B] Trim tabs (or flaps) – The same round disc anodes are usually mounted to the trim tabs.

C] Propellers – To protect the propeller shaft and nut, a propeller nut end anode is used. This is fixed to the brass propeller nut and stopped rotating by an internal hexagonal mating form or a taper and keyway.

D] Propeller shafts – there are two main types, namely eggs and collars. They are clamped in position on the shaft. Due to their small surface area compared to the exposed shaft, they have only a limited effect.

E] Hulls – This section has the most variants in design, fixing styles and weights. They can be welded on with extended steel straps or, in most cases, bolted in place. On steel or aluminium hulls, there will be many anodes fitted to stop corrosion. In GRP and wooden hulls there will be far fewer and they will be mainly protecting metal fixings. This type of anode has a different style depending on the historic favourite of the boat builder's region or industry. They all carry out the same function, and it is only the attachment which varies.

F] Bow thrusters – The propeller ends of the bow thrusters have specialist small anodes fitted.

G] Engines – Engine blocks are protected by pencil anodes held in brass holders positioned in various parts of the water channel of the engine block. It is important that these are checked and replaced regularly, to fully protect the engine.

H] Engine outdrives – Whatever the style of power output of the engine, whether it be saildrives, sterndrives or separate outboards, they will all be fitted with multiple specialist anodes to protect the parts and the lifting rams. 

The condition of the anodes at the time of inspection is an important indicator of their suitability for your application.

If you have any questions about the suitability of your anodes, talk to our friendly sales team, who will try and answer your concerns or at least know a man who can. Phone 01794 523 007 or email anodes@anodesupplies.com to talk to one member of our team.