No two ships sink in exactly the same manner. Comparing Britannic with Titanic beyond certain overall design parameters is a dicey proposition. The nature of the damage, the pre-damage condition of the ships, the damage control efforts, and even the watertight subdivision of the two vessels were all substantially different. Add to that a different depth of water and the result is two completely different incidents.
Titanic foundered in deep water from damage and ingress confined to the bow. This caused the bow to tip down, while the stern was raised. Images of a teeter-totter come to mind. When one end goes down, the other must go up--unless the strain on the board is too great and it breaks at the fulcrum. There was no exact analog to a teeter-totter fulcrum in the case of Titanic, but otherwise the strain of raising up the stern overcame the strength of the hull.
Conventional wisdom hold that compressive forces on the keel caused the bottom to fail first. Having had the privilege of looking at extensive video of those two "missing pieces" of double bottom, I am convinced the classic compressive failure did not occur. None of the signs of such failure, such as the "washboarding" or "accordioning" of the steel are evident. The classic evidence of failure of a steel structure is a rippled appearance not unlike that of an old-fashioned washboard or the bellows of an accordion.
There are none of these classic compressive failure appearances. No ripples mark either of the two pieces of double bottom which came out from beneath boiler Room #1 at the epicenter of the break. Rather, the exact opposite appears the case. The pieces appear to have come out of the hull while in tension.
Once again, Titanic seems to be toying with researchers. The more we learn, the less we seem to know. Answering one mystery seems to open two more enigmas, each larger than the first.
My friend Roger Long has suggested the expansion joints, and the design of those joints, as the first point of failure. Personally, I favor what he suggests, although my opinion is not that of a trained engineer. It seems to me that something must have caused the sides to fail before either the upper decks or the double bottom.
I'll leave any analysis of how the breakup progressed to those with the training in stress analysis and strength of materials. From a practical standpoint, however, none of that matters to the outcome of the night. Once the hull was compromised, it had to bend, break, and tear itself apart.
Whether the expansion joints were poorly designed, or the best ever, isn't worth arguing. The use of these joints proved to be only a stopgap measure until better ideas prevailed. Naval architects over time learned these joints caused more problems than they solved, so better ways were found to allow lightweight superstructure to be piled up on top of the hull girder.
Titanic broke because the strain on the hull exceeded its design strength. The hull was simply too weak to raise its stern up out of the water by a flooded bow. So what? No passenger ship is designed to be that strong. To do so would be a total waste of money not likely to save one soul. By the time Titanic (or any other ship) reached breaking strain , the vessel was already consigned to Davy Jones. The breakup may have increased the speed with which Titanic disappeared, but sinking was already inevitable.
-- David G. Brown
