High-Torque Fish-Friendly Slow-Current Logarithmic Spiral Turbine

Selected from testing of of COTS toy kite turbines, a possible solution to dam-free hydropower for sensitive fish populations.

A video clip of power from a small stream.
https://www.youtube.com/watch?v=4AvHc5GMIwI

A version suited to target rip-tides from remote beaches.

This sort of turbine requires gearing for effective electrical generation. Paradoxically, Archimedes’ Screw turbines easily exceed Betz Limit disc-assumption by developing power along a cylindrical volume.