If we're talking about the spar-type hywind base in the video: Its catenary mooring system resists rotation of the turbine hull. How much so, I can't say. I s

If we're talking about the spar-type hywind base in the video: Its catenary mooring system resists rotation of the turbine hull. How much so, I can't say. I suspect that by far the greatest rotational forces exerted on the structure are coming from wind, not from water, and these would result in low-frequency motions that could be countered by the already rotating nacelle. The smooth spar structure means that surface waves and currents don't result in huge moments about vertical.