Contra rotating propellers are mainly used in aircrafts for propulsion. Here in this video contra rotating system is implemented using five helical gears that has four different sizes but all have same module and tooth pitch.
Contra Rotating Propeller is a system of two propellers placed one behind the other on a suitable drive shaft of the same engine spinning in opposite directions by employing suitable gear drive system.
Contra rotating propellers have been found to be between 6% and 16% more efficient than normal single propellers. However they can be very noisy, with increases in noise in the axial (forward and aft) direction of up to 30 dB, and tangentially 10 dB.