eli5: I was just reading about modern submarines on Wikipedia such as the German type 212. Why are they capable of travelling faster submerged than surfaced?

Question

I would have thought that the opposite was the case as less mass is pushing against the water while surfaced.

In: Physics

Answer 1

Boats slice through the water basically, pushing it out to sides, and they can be designed to lower the turbulence (which creates more drag). Subs are designed to slip though underwater with low drag, low turbulence. But they don’t have a bow designed to minimize turbulence when the hull is breaking the surface. The nose pushes water up over the front of the hull, and then it collapses back at the sides, creating a lot of drag.

Likewise, WWII subs were pretty quick above water, but very slow underwater.