A lashing system is usable on cargo ships that are transporting shipping containers, optionally as a supplement to standard lashing bridges provided on cargo ships. The lashing system includes a support that can interface with the pre-existing interlocking system provided on the shipping containers. The support can be lifted and placed on a stack of shipping containers using the same cranes used for loading and unloading shipping containers. The lashing system includes lashings that are attached to the support and are releasably connectable to another shipping container or to a structure of the cargo ship. The tension in the lashings is preferably monitored during the trips of the cargo ships.