Water, more specifically the chemicals and salts dissolved in it, can be extremely corrosive to boats and particularly the metal parts that come into contact with it. This corrosion needs to be considered and countered if you are going to stay afloat in safety. When metal corrodes it starts to dissolve and return to a more natural state. Corrosion is electrochemical in nature and requires an electrochemical cell to be set up which allows a current (albeit usually small) to flow through typically two dissimilar metals. In order to stop the key metal parts on your boat corroding it is necessary to put a sacrificial metal, typically zinc, as one of the electrodes in the electrochemical cell. These take the form of zinc billets fixed to the underside of the boat. The fixing bolts are then connected internally to all metal parts in the boat paying particular care to provide an electrical link through flexible couplings. As these sacrificial anodes dissolve it is important to check and replace worn ones on a regular basis.
