While submerged, submarines can travel faster than when they are on the surface. As water is more viscous and dense than air, causing more friction, how can it travel faster while travelling through a denser medium.
In: 11
Hydrodynamics (shape). Submarines that are built to run on the surface, like U-boats in WWII, *are* faster on the surface than fully submerged. But that requires building a bow and hull that’s optimized for a surface wake.
All that stuff isn’t helpful underwater…it actually hurts. Optimum hydrodynamics underwater are a nice radially symmetric tube-ish thing, like a missile or torpedo (for the same reasons). But it sucks at the surface because the bow doesn’t split the water, the water goes up over the nose then falls off the sides. That’s why modern submarines at the surface have such a weird looking bow wave.
Edit:
Here’s an example of a U-boat wake: [https://www.uboatarchive.net/U-161A/U-161-81976.jpg](https://www.uboatarchive.net/U-161A/U-161-81976.jpg)
And modern sub: [https://qph.cf2.quoracdn.net/main-qimg-12efafe3d27291abe4d48c185aca313a-lq](https://qph.cf2.quoracdn.net/main-qimg-12efafe3d27291abe4d48c185aca313a-lq)
See how the U-boat is cutting through the water and the modern sub is pushing that giant pile in front of it? That pile is draggy.
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