Dear Yulin,
The OC3-Hywind specifications were derived from data received from Statoil, but these data did not contain a break out between the ballast and steel parts of the spar. Some members of OC3 tried to reverse-engineer the ballast and steel parts from the overall mass/inertia/cg properties of the OC3-Hywind spar, but these were never “officially” prescribed.
Best regards,