Gearboxes are redirecting the rotation initiated by the pedals by a ninety-degree-angle from the crank's axis to the shaft's and the propeller's axis, and if desired, they also adjust the spinning ratio to the desired RPM-speed of the propeller.
Expert knowledge and research have shown two makers' products to be excelling for the HPB's needs. There might be other fine gearboxes out there, but these have been tested by superb designers of HPBs and have proved successful.
The OpenWaterbike's active members wish to help you building your own human-powered pedal-boat. Therefore we are presenting information and recommendations about products that are specially suited for these purposes.
If you can provide or recommend this component, please contact us!
Our boat is better than my boat.