From Elon's AMA: How would the Falcon 9 would be secured onto the deck of its autonomous spaceport drone ship? "Mostly gravity. The center of gravity is pretty

From Elon's AMA: How would the Falcon 9 would be secured onto the deck of its autonomous spaceport drone ship? "Mostly gravity. The center of gravity is pretty low for the booster, as all the engines and residual propellant is at the bottom. We are going to weld steel shoes over the landing feet as a precautionary measure."