If the steady state losses ( Couettte flow analysis example ) indicates a drag of around 50 KW at a Tip speed of 25 m/s. We could expect it to be more at 33 m/s but compared to the system power of 375 MW in 11 m/s winds that loss is tiny.
The energy dissipated can not be more than the drag on the system.
The rotational speed is around 1/4 RPM at the surface and the depth of and within the systems diameter.
It is slower with increasing depth.
It is also slower the further out from the systems diameter.
It is most unlikely that it will create a whirlpool.