There are ways to take data derived from both experiment and theory and turn it into general maxims/guidelines about the effects of nuclear weapons, but a lot of the concrete knowledge we have about that is from setting off bombs near things and seeing what happened to those things. In the case of ships, there were several tests that involved setting off nukes near ships and seeing what the effects were at different distances, on different kinds of ships, on animals on said ships, and so on. The most famous of these was the Operation Crossroads series in the summer of 1946, the very first set of nuclear tests after World War II, in which the US detonated two atomic bombs in formations of scrap World War II vessels. It was the most public American nuclear test series ever conducted, being broadcast simultaneously and with representatives from many nations, including the Soviet Union, being allowed and encouraged to attend. I have written at some length about it here.