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It's what's known as a sacrificial anode and that is it's purpose.

To explain let's look at batteries and morespecificallyelectroplating:


Two types of metals with differing electron weights when immersed in an electrolyte produce an electrical circuit, where displaced electrons 'Flow' from one metal to the other. This is the principle of the leclanche cell and the modern battery. When the electrons flow, they take the molecules on the anode of one metal and plate the cathode of the other metal. This is why a battery dies after a while. If we do this on purpose we call it electroplating.


With that in mind, now consider a ship.


It's made primarily of steel (The cathode). If the paint flakes the steel becomes in direct contact with the salt water of the sea (Theelectrolyte) and most ships propellers are made of Bronze (The anode). This makes a ship a huge battery and just like a battery the bronze propeller would get eaten away by electrolysis.


To prevent this a "Sacrificial anode" made of a morereactivemetal (further away in the periodic scale than bronze) than the one it is protecting is bolted to the ships hull. It is that which is eroded away by electrolysis rather than the very expensive bronze propeller. Zinc is cheap, bronze is not.

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12y ago

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