My boat sits on a boat lift and the propeller gets a white or grayish buildup on it. What is this and how can I prevent it?

This occurs mostly in saltwater environments but can sometimes occur in freshwater.  The buildup you are experiencing is most likely calcium or lime deposits left on the propeller after the water evaporates away.  In most cases these deposits can be rubbed off easily, sometimes even just with your fingernail.  If you experience this, try cleaning with a calcium lime & rust remover.  Remember to rinse the propeller thoroughly with soap and water after each use and keep a protective wax on the propeller to prevent further calcium buildup.