People generally use sacrificial anodes to protect the ship, the sacrificial anodes are corroded away, and the hull, stern drive and shaft are protected, because the anode metal can freely emit electrons instead of being corroded by the protected structure, hence the nickname "sacrificial anodes".
For Marine sacrificial anodes, how to choose zinc anodes, aluminum anodes and magnesium anodes
Now, most shipowners refer to sacrificial anodes as "zinc blocks" because zinc has been used for a long time, but sacrificial anodes are not just made of zinc. Aluminum and magnesium are also common materials for sacrificial anodes and perform better than zinc anodes in many cases, depending on the type of metal to be protected and the nature of the electrolyte. The higher the anode voltage, the easier it is to release electrons, and the more likely it is to cause self-corrosion.
Magnesium has the highest negative voltage, and in theory it should be able to protect any metal, but in reality this is not the case. The anode generates current by generating a potential difference between the electric couple sequence, and the potential difference between magnesium and the protected body is often larger, so magnesium can provide more protective electrons faster, but its high potential results in its protection time is only one-third of zinc and one-fifth of aluminum. It is assumed that zinc can last 150 days, magnesium can only last 50 days, and aluminum anode can last 225 days. In addition, magnesium also causes another hazard, which is over-protection due to too high a driving potential.
So how do you choose which anode to use on a ship? Cost is an extremely important consideration. Magnesium is more expensive than zinc, and zinc is more expensive than aluminum. In addition, compared to zinc and aluminum, zinc forms an insulating oxide film, especially in fresh water, which prevents the zinc anode from working properly. If the sacrificial anode is never consumed, then you should be careful, it may be oxidized and not doing its job! The sacrificial anode should be replaced in time.