It's quite remarkable when you imagine that it's 2" plate bending about like that (I'm guessing of course).
I know nothing about ship building, but it would be pretty thick stuff.
Years ago I had a windscreen shatter on the M6, (shatter, shows how long ago) at about 10pm on a section of viaduct. It was raining heavily and dark and couldn't drive beacause I couldn't see anything.
I phoned the ES and they said pull over as close to the parapet as you can and stay in the car. Every truck that went past caused the deck to flex, especially when more than one passed at the same time.
I was stuck there for a good 90 minutes and TBH, I felt quite seasick most of the time. I know the construction of that section and it's 1.8 m high steel box girders with strengthening webs internally, and there's even strengthening to the webs. I spent a working week inside them once, measuring up the welds.
It's thick stuff, close to 2" and it bounces like a trampoline.
That was in the early 70's, imagine how many trucks have been over it, how many oscillations that deck and it's beams have done, since then.