These heavy lift deck ships have a multitude of large ballast tanks below to give the massive stability and large righting arms (GZ in stability terms) that is needed. In fact most of the under deck spaces are dedicated stability tanks. The trick with these is not to give them too much stability as the roll rate becomes too snappy and the acceleration moments on the very tall structures become greater than they are designed for and they break. (I’ve seen several like that where I was part of the damage investigation).
Looking at the size of the ship I would estimate it’s deadweight carrying capacity to be about 12,000 tons. The load looks to me to be less than 2,000 tons as windmill blades are actually quite light, relatively speaking, and the vertical columns are hollow. The vessel is low in the water which indicates a full load so she is likely carrying up to 10,000 tons of water ballast.
It would likely be a comfortable ride.