How do sliding caisson gates close the entrances of dry docks?

In the context of civil engineering for harbors and sea works, a sliding caisson gate is a common design used to close the entrance of a dry dock.

These gates are typically housed within a recess, known as a camber, located at the side of the dock entrance. To operate the gate, it is moved into position by being hauled across the entrance using winch and wire rope gear. When the dock needs to be opened, the gate is drawn back into the camber to clear the passage for a vessel.1

To ensure the dock remains watertight, the gate relies on the pressure of the water outside to provide a sealing force against the dock's structure. Effective sealing often requires specialized contact faces, traditionally achieved using timber linings on the gate that bear against polished granite stops, though modern alternatives such as stainless steel bars and rubber linings are increasingly utilized.1