This invention provides a method for installing a self-floating deck structure with at least one recessed cavity on the bottom of the self-floating deck structure onto a buoyant substructure. The self-floating deck structure is aligned over a submerged buoyant substructure and the top of the buoyant substructure is inserted into a recessed cavity in the self-floating deck structure until the buoyant substructure mates with the self-floating deck structure at a point above the water surface. The self-floating deck and the buoyant substructure are connected by welding or one or more mechanical device.