The most asked question at the boat shows is almost always” what is the difference between a 3 blade and a 4 blade boat propeller” The difference between 3 blades over 4 blades is that the 3 blade (smaller blade ratio) usually goes faster and the 4 blade (higher Blade ratio) is better hole shot and betterstern lift as well as better handling and fuel economy because it will keep you on plane at a lower speed
If you look at a propeller from behind, and visualize a circle that the blade tips would draw, you will see that the blade of a 3 blade prop covers about 50 -55% of the circle. (This is called diameter area ratio, or DAR). You can add thrust within this drive circle by increasing that percent (to say 60 – 65%) by adding a 4th blade. When you look at a four blade prop you will notice that more of this area is covered because of the extra blade. That means more push contact with the water.