Not impressed , bloody awful idea,(reply>), @Mn M If it has to have a rope stretched across the river in order to function why  not just use the rope as a drive and pull yourself back and forwards with the rope , either with a small engine or even hand-cranked, far less  precarious than relying on eddy currents to push you across , more reliable , tried and tested in various places around the world including India and Africa , more safe and capable of heavier loads .,(reply>), Why though?