""I was under the impression that double skinning was more about containment of internal leaks rather than impact protection.""

I believe double skinning was first introduced for bulk oil carriers, as an added safety measure to minimize spilled oil from collisions and other incidents. I believe this has expanded to include some other bulk carrier ships, where environmental issues are not as big a concern. The link below has some historic infomation.


Double skin

""Anyone know what the double bottom config is 'supposed' to be able to withstand?""

I suspect this question has a highly technical answer, and would depend on matters such as vessel design/construction and use, the material used, the type of stress/incident. Below is some very technical information, that I am unsure adds much, but will link anyway)

Some tech info

bulk carriers