I assumed that when the ship went over on its side, the waves filled the sails with water and held it down, and the hatches were open because there were 60+ people coming out of them. While they were climbing out, the water was probably going in, more weight to hold the boat on its side.

They were already expecting a storm, that's why they had lowered most of the sails, but they couldn't lower them all or they couldn't control it. It was apparently the microblast that knocked the Concordia over, and the rest of the storm conditions assisted in preventing it from righting itself. It's often the combination of circumstances that causes major problems, not just one thing by itself.

I've got a 30x50' piece of plastic sheeting in my open field, held down very nicely with little lakes of water. Wind? No problem!

Sue