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. For more details, visit https://underwaterdivingblog.wordpress.com/2021/09/16/underwater-maintenance-brief-introduction-to-boat-zincs/