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In order to choose the best propeller size for any boat, it is important to first identify the intended use of the boat. Fishing boats and speed boats use similar propeller sizes, however, the fishing boat must also be able to operate for extended periods at low speed. A boat that will pull skiers or wake boards will require a propeller size that features great pulling power and power out of the hole to get the skiers up and going. Water depth and bottom content are also factors to consider when choosing a propeller. For shallow water with a rocky bottom, a smaller propeller will give more clearance and prevent potential damage from contact with the rocks.
With all factors being equal, a larger propeller size will give more power, but less speed, than a smaller propeller size. The large propeller blades are able to grab more water than their smaller counterparts, so the larger propeller size will produce the power to pull the boat up on plane quicker as well as pull the skiers up and out of the water with the least amount of propeller slip. A smaller-diameter propeller will allow the motor to rev higher, causing the propeller to spin faster; however, the propeller will also slip in the water more without moving the boat forward.
If the boat is designated for extended slow-speed use, a larger propeller size will allow the motor to operate at a much slower speed while maintaining a steady and slow speed. The larger-diameter blades are better able to grab the water and exert force to drive the boat through the water. This is also the propeller of choice to save the most fuel. By pulling the boat at a slower operational speed, the same distance can be covered while turning the motor the least amount of revolutions, thereby saving fuel.
For a boat that will be used for high-speed entertainment, a smaller propeller size will allow the engine to operate at a higher speed at the hit of the throttle. The smaller propeller will slip in the water a little, allowing the engine to come up to speed much quicker than a larger propeller will. By cupping the propeller blades, a smaller propeller size is able to grab and push more water than a larger flat blade. This allows the smaller propeller size to propel the boat very fast in a short stretch of water and maintain the speed without placing a great deal of stress on the tight and compact propeller blades.