I did get this to work on my VEC 500, although power was very low at the time; around 190 W when sailing at 6 knots. Bear in mind that this was with a motor directly mounted on the prop shaft - WITHOUT and reduction gear. Unfortunately there doesn't seem to be a way to turn of the cycle of 15-beeps when re-gen is engaged.
I've now rebuilt the transmission with a reduction gear, and therefore expect higher power, since the motor (generator) will spin faster for the same sailing speed. I would estimate the generated power to be about 500 W, this have to be confirmed with real life tests though.
You can read more about re-gen in
this blog post