USS Patrick Henry hull degradation

At the DARPA composite-submarine workshop, photographs of the Patrick Henry (just then approaching disposal off the Virginia coast) showed dozens of hull cutouts accumulated over 30 years of service — used to argue to the composites team that submarine hulls must be cuttable and repairable.

They have this three-day workshop, and the first day they talked to us about the requirements of building a submarine. A guy got up and showed the Patrick Henry, which had just finished its life and was about to be blown up off the coast of Virginia and sunk to the bottom of the Atlantic. It showed a picture of all the cutouts in the hull it had had in the previous thirty years, and it looked like a patchwork quilt — dozens of holes cut in the sides. Then they broke us up — the metals people on the second day and the composites people — and we went our separate ways. On the third day, on the half day, we came back to report.

Tom's 1988 picture of the Patrick Henry showed a "patchwork quilt" of hull penetrations. Used to make the point that hull lifetime is limited not by the steel's corrosion or metallurgy but by geometric deviation from a perfect cylinder after thirty years of cut-and-reweld work.

Well, that's assuming you never cut through that hull in the previous thirty years. I remember seeing a picture of the [Patrick Henry] back in 1988, and it looked like a patchwork quilt, with all the penetrations. If you just built your hull and never touched it for the next thirty years, it'll last another thirty years, or a hundred years, as long as you keep your zincs on, your cathodic protection. But when you start welding other things on it, it no longer has that 30-foot-diameter circle or 20-foot-diameter circle accurate to whatever millimeters. Not very many, right? It's a pretty perfect circle. Once it's thirty years old, I've done so many penetrations, that thing won't have the same depth capability because it's no longer a cylinder — it's sort of a funky cylinder. I bet when they were evaluating it, they were measuring diameters at different positions and saying, is this hull worth saving? But it's not from corrosion or metallurgy of the hull — it's from the structure, the geometry of the hull.