What chemical method can be used to guard a ship's gate

        Electrochemical protection methods.

         First, impressed current cathodic protection, impressed current cathodic protection. The gate can be connected to the negative end of a power supply, and the positive end to a piece of carbon. In this way, the iron gate forms the cathode of the electrolytic cell and is protected. 

        The second method sacrifices the anode for cathodic protection. The gate can be wired to a metal more active than iron, so that the gate and the active metal form the two electrodes of a galvanic cell. The     positive electrode of the galvanic battery is protected by the less active iron gate.