Dry Dock 3 Caisson Replacement and Seat Repairs: A Novel Approach to a Major Rehabilitation of a Continually Operated Naval Dry Dock

Dry Dock #3 (DD3) is one of two docks at the Portsmouth Naval Shipyard (PNSY) in Kittery, Maine, that’s suitable for the servicing of the Virginia Class submarines. The shipyard’s primary mission, to overhaul and repair submarines, places the dock to be under continuous demand. Nearing 60 years of service, the dry dock required major rehabilitation to the entrance structures, and replacement of the caisson gate to assure continued operational capabilities well into the future. The challenge? How to rehabilitate the dry dock entrance structures and caisson gate without taking the dock out of service. The solution? A mini-cofferdam was designed that was large enough to allow a few workers to enter and complete the concrete removals and reconstruction, at 20-feet below the water surface. This type of structure, often referred to as a limpet, is common practice for ship repairs; however, it’s seldom used to repair waterfront infrastructure.