How do fender chains protect the Panama Canal lock gates?

Fender chains serve as a critical safety barrier for the Panama Canal lock gates by preventing vessels from colliding with them. Before a ship enters a lock, it must pass a fender chain stretched between the walls of the approach.1

If a vessel is proceeding at a safe speed, the chain is lowered into a groove at the bottom of the channel to allow passage. However, if a ship is moving too rapidly, the chain remains stretched across the path. Should the vessel strike the chain, it is designed to pay out slowly via hydraulic machinery, which gradually brings the ship to a stop. In the event that a vessel breaks through the chain and continues toward the lock, a secondary gate positioned 50 feet away provides an additional layer of protection to arrest the ship's advance and safeguard the primary lock structure.1