Remember that the structure of the Derbyshire was basically a long steel box, divided into nine holds, each with a pair of huge hatch covers over the top, and a bow and stern section on the ends. Unlike most other ships of its size, its interior was mostly empty space, without much internal bracing.
We knew that the Derbyshire was lost in a very strong typhoon (hurricane), so there is no question that weather conditions were extremely heavy. What we didn't know was why the ship couldn't cope with the heavy weather, as it had before, and as other ships of its class do.
The bulkheads, and the frames around them, are numbered from the stern of the ship to the bow. The Derbyshire had a joint in the main girders at Frame 65 (just forward of the stern superstructure). The two lengths of girder were butted against either side of the bulkhead, and welded there to make the join as strong as possible.
Theoretically, if this joint was made correctly, it should have been strong enough to meet the ship's design goals. A problem might arise if the two ends of the girders were not correctly aligned. (Remember, the girder ends are butted against a bulkhead, so you can't easily see the other side to make sure that the two sections line up.)
If the girders were misaligned, the flexing of the ship at sea would cause tremendous stress at this joint, and sooner or later the bulkhead would fail. This actually happened to one of the Derbyshire's sister ships, in shallow water close to the coast, so all the crew were evacuated safely.
Based on this, some people concluded that the Derbyshire must have experienced a structural failure at Frame 65, causing the stern superstructure (where the crew lived) to break off and sink almost without warning. Although there was no direct evidence, these people (primarily the families of the crew, their lawyers, and some media investigators) accused the shipbuilder of conspiracy to hide the facts, which might point to their liability.
This page maintained by Wil Howitt