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Luckily it never happened on my projects. But things that could go wrong were numerous.
A lot of the work was in harbors or protected waterways, so they used a lot of crawler cranes on barges. If they tried to lift too heavy of an object they could unbalance the barge and tip it, or it could buckle the crane boom, or snap a load cable. All of these are extremely dangerous problems.
For ships/barges stuck on rocks or other obstructions, the danger can be creating an unbalanced condition which would cause the ship/barge to roll off the obstacle. Also, once enough weight is removed the ship/barge could become buoyant and suddenly become a large moving object in high wave conditions, etc.
Basically, the engineer is there to help figure out weights, centers of gravity, centers of buoyancy, etc. But it was always guess work as to what to assume for weights of various areas of the ship, especially areas too dangerous to access due to flooding, or the chance of the ship breaking up under wave action, etc. Mildly interesting, but not always worth the liability. And to be honest, the salvage superintendents were often just as good at guessing the weights by eyeballing it as the engineers were at trying to calculate it. The difference was, if they were wrong and something went wrong, they had less recourse in legal terms to defend their decisions than an engineer who could show calculations, etc. At the end of the day, the only folks who really make money in any of the situations, good or bad, are the lawyers.