First of all, if you want to protect the cathode by electrolysis, you have to connect the entire hull to the power supply, which means the whole ship is electrically charged. And water is a good conductor. Wouldn't you be afraid to electrocute everyone on board?

        Second, most water in nature is slightly acidic because of the carbon dioxide dissolved in it. If the impressed current is used to protect the cathode, special attention should be paid to the fact that when the current is too strong, the cathode gathers a large number of electrons, making the H+ electrons in the water become H2. Hydrogen embrittlement.

        Third, although the voltage of the external power supply does not need to be too large, but a long time to power will also cause a waste of electricity, power supply should also be regularly maintained. The method of sacrificing the anode Zn to protect the cathode is not needed after the Zn is ready, and it is good to replace the new block after three or five years. Compared with the impressed current, it is much more convenient and saves the cost of manual maintenance.