What are Anodes on a Canal Boat?

Did you pay attention in school during science class? No, us neither. As a result, the term ‘anode’ might sound a little technical. Well in truth it is, but today we are going to get all scientific and give an answer to the question “what are anodes on a canal boat”? It is actually really interesting, so read on and we’ll learn together.

What is an Anode?

Well, let’s start simple. An anode, on a canal boat, is a lump of metal that is attached to the hull below the waterline. Its sole purpose is to degrade and rust away over time. There is a very good reason for this …

Why do Canal Boats have Anodes?

Still with us? Good!

Ok, let’s ask you two questions. Have you ever got a piece of tin foil on a filling? How did it feel? What actually happened, as you swore in agony, is that an electrical current was generated across the nerve in your tooth.

Why did this happen?

Basically, the mixture of two different types of metal (the foil and the filling) and an electrolyte (your spit) caused a tiny reaction that made an electrical current… Electrons passed from the foil to your filling via your spit… This is also exactly how a basic battery also works.

And why is this relevant?

The same thing happens to the hull of your boat. The water of the canal contains lots of minerals, salts, and other chemicals that make it a really mild electrolyte. The hull is made of metal (often a blend of metals) and becomes ever so slightly electrified… Constantly. It will also react with other metals such as that of the prop and prop shaft. When a metal is electrified it starts to shed particles, and essentially corrode.

This reaction is only tiny, but is ongoing, constantly. As a result, and over time, your hull will get thinner and thinner as particles are lost. Ok, it would take hundreds of years to wear through completely, but over a long enough time, it is really pronounced. Your hull getting thinner could never be seen as a good thing.

So how do we stop this?

Well, we can’t stop it entirely; it is physics after all… but what we can do is reduce it by using an anode.

What Does an Anode do?

It’s quite simple. As we have already said an anode on a canal boat is a lump of metal that sits under the waterline. It reduces the effects of corrosion due to electrolysis, as it corrodes before the hull.

The reaction we talked about above happens when there is an electrical current between two different metals. By attaching a more reactive metal we can ensure that this reaction or electrolysis happens to the more reactive metal. In its most basic explanation, it will shed its particles instead of the hull.

What are Anodes on Canal Boats Made From?

The general material used for canal boat anodes is magnesium or magnesium alloy. But this isn’t the same for all boats. In brackish water (which is a mixture of seawater and freshwater) you will tend to find that boats will use aluminium nodes. In pure seawater, you can expect to see zinc anodes.

What is the difference between the different types of water we have mentioned above? That’s right there is more salt. What this means is that the electrolyte is stronger, and therefore the electrolysis or loss of particles happens at a quicker rate. Magnesium is quite reactive, so if you were to use it in salt water or brackish water, it would degrade far too quickly. Aluminium and Zinc, are less conductive, so will degrade over a longer period, whilst protecting the hull in the same way.

Are There Other Ways to Protect a Canal Boat?

There are a couple. The first is to remove it from the water entirely. Ok, that is probably not an option.

The best way (aside from fitting anodes) is to ensure that your hull is painted or blacked at least once every couple of years. This thick paint seals the hull and prevents molecules from being lost.

Now if you have been paying attention you will have gathered that the makeup of the water does make a difference to how quickly a hull degrades. You will find that boats that have been moored in mineral-rich water will be subject to higher degradation. If you are wintering your boat, it might be worth changing location!


Anodes are relatively inexpensive (well at least compared to a new hull) and are really effective in reducing the effects of electrolysis. If you are going to moor your boat in a tidal river or a particular mineral-rich area, then they are definitely worth considering. Hopefully, you’ll now be able to answer the question, what are anodes on a canal boat for?

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