To prevent this from occurring, various. types of "mud motors" were developed. "Mud
motors" offer a direct drive shaft to the propeller. These motors have an air cooled
engine and do not require the river water for cooling. With the boat "on-plane" (boat
bottom parallel with water surface) the weight of the boat is distributed evenly and the
prop needs less torque to displace the same amount of water. Direct drive propellers are
capable of cutting through mud and sand.