Propellers  What does the propeller do? A propeller converts the rotational energy generated by the engine into thrust to push the boat through the water. Discounting the propeller's blade design, the larger the propeller, the more efficient it will be in pushing the boat forward. The problem is balancing the propeller's size with the motor's ability to spin it.
 Propellers are often referred to as screws, this is a result of the way they work in water. Each turn of the propeller moves it linearly forward by the amount of its pitch assuming it was running in a solid medium. This is similar to turning a screw into a block of wood. Of course the propeller is not 100% efficient, nor is water a solid medium. Under actual operating conditions, slip occurs as the propeller rotates resulting in the absolute forward movement (actual pitch) being less than theoretical pitch.
 Cavitation occurs when the pressure on the forward face of the propeller blade becomes low enough that vapor bubbles form and the water boils. As the vapor bubbles pass over the blade face and move away from the low pressure area, they collapse and condense back into a liquid. The collapsing of the vapor bubbles might seem trivial, but it is a very violent event which can result in the pitting of the propeller surface. Cavitation is a major source of propeller damage, vibration, noise, and loss of performance. Cavitation can be caused by nicks in the leading edge, bent blades, too much cup or simply high boat speed.
Ventilation or aeration occurs when surface air is drawn into the propeller blades. When this happens, boat speed is lost and engine RPM climbs rapidly. This can result from excessively tight cornering, a motor that is mounted very high on the transom, or by over-trimming the engine. Ventilation is most often confused with Cavitation.  A surface-piercing propeller is a propeller that is positioned so that when the boat is at full speed the waterline passes through the propeller's hub. This is accomplished by extending the drive shaft out through the very bottom of the transom. When running properly only one blade of a two bladed propeller is actually in the water. The surface propeller is very efficient at minimizing or eliminating cavitation by replacing it with ventilation. With each stroke, the propeller blade brings a bubble of air into what would otherwise be the vacuum cavity region.
Propeller Chart This chart was generated from many sources and put into a spreadsheet so it could be sorted first by diameter and then by pitch. It includes Octura, Prather, RRH and ABC. Not all the props are include but a significant portion of them are represented. Propeller size/pitch table | 
