If you are buying a used boat, or just maintaining a boat, the zincs – hull anodes or sacrificial anodes – are an essential part of her protection. Boat zincs which are not working can lead to a fatal failure of thro-hull fittings. Many boats have sunk on their moorings because the boat zincs were not replaced or fitted in the first place.

Source: https://www.barnaclebusters.com/services/underwater-yacht-maintenance/