I can't provide any specific info on that, but *if* the devs didn't remove code from SH3 when they did Sh4, it might be related to sub displacement. The smaller Type II Uboats clearly rocked more around than the Type IXs, so I would first try setting a much lower submarine displacement and see if that produces a result or not. Once you know if the effect is still there, you can try to see if it can be configured elsewhere
