American brute force engineering. Just add more horsepower.
Iowa machinery was a work of art, though. People will argue about USN design decisions, or a hundred other things, but to my knowledge the quality of their machinery has never been called into question.
No need to get stupid. If you make a ship that's 100% machinery you've obviously gone too far. Unless you're Turbinia, and the point is to demonstrate how awesome steam power is.
From what I understand that's only the listed horsepower, with the actual being a fair bit higher still.
Basically all engineering plants have a designed overload above list power. I don't doubt that Shoukaku and Graf could both produce more at those setting too although unlike the more detailed stats for famous classes like Iowa such numbers are harder to find. In Iowa's case the design overload on the plant was about 20% for around 254,000 maximum possible HP.
This was to be used only if really needed, and it wasn't often needed since speed trials produced speeds of about 32 knots at a very modest (4%) 221,000 HP overload at a representative full load displacement of about 57,000 ton displacement. Supposedly speeds up to 34-5 knots were attained at (unlikely) lighter loads and full overload. The ship was considered good for just shy of 31 under normal operational conditions of average sea states, bottom fouling, and design power.
Wasn't there a post about how that 212,000 HP was actually a 20% reduction of a 20% reduction because of a documentation issue? I remember there was a post about it somewhere but I could be mistaken on the numbers...
EDIT: Ah found it. It was two 10% reductions, not two 20% reductions. Referencing the original horsepower post with the comment by grand zero:
grand zero said:
256,520shp maximum/212,000shp listed, actually.
The US has this thing for listing specifications far on the side of caution. In the case of Ship's Engines, they design in a 10% 'safe overload' buffer zone that can be safely used without any damage whatsoever (beyond normal)to the boilers and turbines, in fact it's not even governed. Basically the 'yellow zone' on many meters. However, in the case of the Iowa-class there was a mix-up where the contractor (General Electric) told the Navy the rating with the buffer already calculated in, at 233,200shp. The Navy didn't realize this and reduced it another 10%, giving us the current listing of 212,000shp. When this came to light everyone involved just found it hilarious and ran with it.