IMG 1724PaulK

The drawings available on this site don’t show much about that. You might try looking for pictures of the setup on listings of other Ensenada 20’s for sale. The one I found definitely had what looked like a Compression Post going from the top of the centerboard case and keelson to the underside of the cabin top below the mast step. The design may vary on different boats, but the idea of supporting the base of the mast is there.