hydro-generator

As the hydro gen. topic is stil discussed....elsewhere ..Ill comment .
Any open(not encased) fluid screw (prop), air or water, if used as generator ,is subject 1st to the Betz limit, which claims a open turbine cannot extract more than 59% of the Actuator disc's energy.
Then there's the efficiency of the turbine, prop, setup, bladeprofile etc. to be multiplied...and friction loss in bearings, gear-reduction, el.generator...
As opposed to a propulsor, having to create thrust in boat axis, the generator must do so perpendicular as to create torque at the prop most efficiently...at 90deg to boat direction?!
So I believe generation pitch must be far greater at same speed AND the camber profile adapted...i.e. ..a different prop.
Thats why dragging a propulsor thru water cannot be closely as efficient as its propulsing efficiency.
I saw results of towtests with q 100ft brig, establishing propchoice for hydrogeneration of their parallel motor/generator. Between 3 dif. props w various pitch and diameter they figured that regeneration came to 25 % to 35% of propellerthrust at that speed. i.e. app 10% to 15% of the actuator disc. The props used were fixe pitch.
Wonder if I got this right?