From behind the boat looking forward to the propeller(s), a right hand propeller rotates clockwise and a left hand propeller rotates counter clockwise. Many single engine boats rotate clockwise using a right handed propeller. Two propellers rotating the same direction on twin screw boats will create steering torque. In other words, two right handed propellers pull the stern hard to the right and the bow to the left.

Two counter rotating (opposite direction) propellers on twin engine boats eliminate this steering torque because the left handed propeller balances out the right hand propeller. This results in better straight line tracking and helm control at high speed.