Originally Posted by guitarguy56
Why re-invent the wheel? These products are here already to buy and install and from the video and the website of the product... it seems a viable product?
and the video
of the product in full use in the water and conversion
Nick: Because the DuoGen is a miserable piece of equipment with corrosion problems and weak output. Because the same piece of equipment cannot work effectively in air at 15kts and water (100 times denser) at 6kts. It's not a good solution; if it were, you would see them on boats rather than on YouTube.
Chuckles: All the above issues were covered in the "Hacking a trolling motor" thread. As Greg says, a propeller is not an effective generating rotor. You cannot belt the shaft because you will lose 2/3rd of your power to pulley or gearbox friction. The very best water generators (Watt&Sea) produce ~500W max, more like 250W at cruising speeds. That isn't 3.5 hp -- that's 1/3 to 2/3 hp. And that's a purpose-designed device, without the inherent compromises and losses of an engine shaft, hacked trolling motor, or air/water combination machine. Supposedly the Ferris units are better than the DuoGen, but they require a substantial rotor conversion.
Water generation is a good solution for frequent passagemakers. That's a fairly small market for a device that is not easy to engineer properly. The OP's idea of a purpose-built, dual-function troller/hydro-gen is perfectly feasible -- but creating one that worked adequately in both modes would take more R&D than the likely sales volume would justify. Pity, cuz I would lust after such a thing.