The monitors have a thin upper deck. Most ships have guns located well above the monitor deck, so their shells usually ricochet off the monitor deck. But guns on floating batteries can, under certain rolling conditions, shoot at the deck of the monitor at an advantageous angle. Then the thin deck will be pierced and there is a high likelihood of a fire. But in general, with a rough sea, monitors are reliable fighters. I do not remember that I was able to pierce their waterline. In addition, monitors are very difficult to ram, because their body is hidden far behind the outer armor.
Yes, ironclad floating batteries did not fight in real history. We were unable to identify the weak points for a lacky shot.
