The propeller on a boat motor is designed to balance the motors output potential with the drag it creates.
Boating propellers operate on the same principles as any other fan. The propeller blades are designed to push the surrounding fluid in a particular direction. When a fan blade has more blades, it pushes more air, or water, through the blades. Whether we are talking about ceiling fans, or boat motor props, the size, shape and weight of the propeller determine the amount of drag on the motor and the amount of thrust it produces, thus affecting the motors performance.
Propeller Thrust
A two-blade propeller has less thrust than a three blade propeller. This means that a two-blade propeller on a trolling motor will not propel the boat as fast as a three-blade propeller can. However, the trolling motor is not designed to propel a boat through the water quickly. It is designed to move the boat slowly through shallow, and weed-filled waters.
Weed Chopping Action
A two-blade propeller on a trolling motor has a greater ability to chop weeds than a three-blade motor. This benefit is based on two features. Because the two blade propeller is lighter, it spins faster, and is more likely to chop the weeds it encounters that become entangled. A three blade propeller spins more slowly. The hydrodynamics of the three-prop blade's shape pulls weed into the water stream because it creates a funnel like thrust vortex. The weeds are more likely to become wrapped around the three-blade prop as a result.
Battery Power Consumption
The actual weight difference between the two- and three-blade props is insignificant when compared to the thrust differential between the two. The additional blade on the three-blade prop engages 50 percent more water surface than the two blade prop. As a result, the three-blade prop pushes more water with each revolution. Therefore, the three blade propeller consumes more energy with each revolution than its smaller cousin, and will drain the trolling battery more quickly.
Drag on the Motor
As mentioned above, the three-blade propeller pushes more water than the two-blade prop, which also creates more drag on the electric motor. Because the propeller produces drag on the motor, boating designers balance a boat motor's power output with the size and pitch of the motor propeller. If these two are out of balance, and the propeller creates more drag than the motor is designed for, the combination can cause the electric trolling motor to overheat, and possibly burn out.
Tags: blade propeller, more water, trolling motor, boat motor, motor designed