Hello Boonbox, we don’t have any experience in traveling to Culebra, but there is an American couple from Florida that has a sailing YouTube channel named GBU ( sailing the good the bad and the ugly), I know that sounds bad but there quite funny. They have a whole series of videos on Culebra and the surrounding islands. They also have extensive videos on their ferry rides to and from the mainland and explains quite a bit about it. I thought you might want to view there video’s to give you a first hand experience of how the ferry operates.
Just a suggestion, I thought this might help you out some.