Most pleasure boats are factory equipped with aluminum propellers. Aluminum is a great choice for small and medium sized boats. They are inexpensive and under normal conditions can last for many years. When boating in an area where striking the bottom is likely, aluminum blades can flex, helping prevent damage to your engine.
Stainless steel boat props are ideal for large or heavy boats and those running in saltwater. Although more expensive than aluminum, stainless steel is more durable and will last longer. When running at speeds over 50 mph, stainless props will perform better than aluminum.