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Asked by anon-258065 on 3 Jul 2020.
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Yueng Lenn answered on 3 Jul 2020:
I’d have to say yes, as submarines can’t travel in air. But if your question is really more about whether air or water produces the most drag to slow down moving objects, then I’d have to say it’s water as its about 1000 times more dense than air.
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Julian Onions answered on 3 Jul 2020:
Well partly it is because they are designed to work that way. There are a couple of things going on, firstly when surfaced the flow around the submarine is less streamlined as it breaks up around the interface. So once it is fully submerged, it doesn’t have that issue. The full answers is a bit more complex, and needs a lot of fluid dynamics to understand!
The other is the deeper they go, the less cavitation around the propellers as the increased pressure stops the bubble forming so readily, so they can more efficiently convert rotation speed into thrust.
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Tom Louth answered on 3 Jul 2020:
Hmm, if you dropped a submarine from a great height it would be operating in air, and would probably move quite fast!
Diesel-electric submarines can only operate their main engines on the surface and rely on batteries underwater. They may be faster on the surface, certainly they can go further.
Nuclear submarines can use full power underwater, and are faster underwater than on the surface. This is because when a vessel is moving on the surface it generates waves. It takes energy to do this which slows the boat down. Submarines are not an optimum shape to minimise this sort of drag so can be a bit slow on the surface.
Comments
Josh commented on :
Submarines are faster when they are fully submerged than when they are at surface. This is due to all sorts of factors like wave generation at the surface and turbulence, and they are designed to travel submerged rather than at surface like boats.