The ship doesn't need to withstand the wave without any damage - that would be unnecessarily expensive. But they should at least be designed to withstand such a

The ship doesn't need to withstand the wave without any damage - that would be unnecessarily expensive. But they should at least be designed to withstand such a wave without sinking. If I climb on a ship and you tell me "well, there's a 1 in 100'000 chance that we'll be hit by a freak wave and then it's quite likely that everyone on board will die, since the ship will be broken in half and sink", that's a very different thing to say than "well, there's a 1 in 100'000 chance that we'll be hit by a freak wave, and then the ship will sustain severe damage but should be able to limp back to shore or at least float long enough for a rescue." The difference between those two scenarios is probably less expensive than you think.