I'm a diesel macanic and I work on ob jet's also 3 bladed alum are softer and ding very easy once they get dinged they get smaller in size when u resharpen them even with a new sleeve they don't push a big load. but the 4 bladed is stainless steel harded materal doesn't ding more blades = suckes up more water and in turn gets up on plane instant works great for me espacially duck hunting w/ deks and guns 4 people and gear in a 18' duckworth keani 115/80 jet I'll never go back