None of them actually have a flat bottom, though. Speedboats (such as the ones I mess around in) have semi-displacement or planing hulls. These have very complex shapes with a predominantly V shape at the front
Well, I shure agree with you on speedboats.
But allmost every freightship today has a flat bottom.
(Ok, they are rounded at the sides, but they still are pretty flat)
In the good old days, ships really had visible keel, but now it is just a stronger beam in the middle of the double bottom.
I don't really understand what you mean with non-displacement hulls.
Ok, a containership or a reefer is much more slender then for example a tanker or a bulker.
No mather how slender they are, they still have a pretty flat bottom in the middle