Why do the propeller of underwater thruster differentiate between CW&CCW

Looking from the propeller nozzle to the direction of the thruster motor, if it is turned to the left, it is forward propulsion, the CCW, and if it is turned to the right, it is forward propulsion, the CW.

The difference between left and right propeller is mainly to offset the rolling moment. All the thrusters in the same direction of rotation are used in an underwater equipment, the rolling moment is not eliminated, and it is easy to turn in circles in the direction.

The CCW propeller and the CW propeller are symmetrical, which can cancel out the roll.