Submarines that don't use compressed air to sink and rise?

  • #1
Summary:
Are there any submarines, or UUVs that don't use compressed air to sink and rise?
I have been wondering about submarines for a while, and especially their ability to sink and rise on command. I understand that they do this through ballast tanks and replacing water with compressed air, which increases the buoyancy force and helps them rise. (I understand that my knowledge is highly superficial, so if anybody feels that they can explain this better please do so :) ). However, submarines can't store an infinite amount of compressed air, so do they have a limit to the amount of dives they can do? I have never piloted a submarine myself, but I do know that many subs have dive planes. In which situations would a submarine captain use the dive planes vs. ballast tanks to rise.

Sincerely,
Richard

Edit: Do smaller UUVs have different ways of sinking and rising than larger submarines?
 

Answers and Replies

  • #2
anorlunda
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I don't know for sure, but I suspect that recreational subs like the one in the picture just use the force of the vanes while maintaining a fast forward motion. They can submerge, but they can't hover motionless underwater.

slask.jpg


By the way, I want one of those for my birthday.
 
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  • #3
Hmm, thank you for the reply. That makes sense. Conventional submarines seem to be able to move like helicopters (Hovering and controlling their buoyancy), whereas subs like the one you showed are more analogous to planes, their thrust and lift (if I can call it that) come in pairs. When a conventional submarine resurfaces, do they refill their compressed air tanks, or do they have to wait until they dock in a port again?


Who doesn't want one of those? ;)
 
  • #4
Baluncore
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When a conventional submarine resurfaces, do they refill their compressed air tanks, or do they have to wait until they dock in a port again?
They do not need to fill with air because they reuse the same air.
The ballast tanks are open to the sea at the bottom.
To dive they compress and store air that was in the top of the ballast tanks, water moves up into the tank.
To surface they bleed stored compressed air back into the ballast tanks to displace some water.
 
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  • #5
Wow, thank you so much. That really cleared up my understanding. Thank you!
 
  • #6
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To dive they compress and store air that was in the top of the ballast tanks, water moves up into the tank.
To surface they bleed stored compressed air back into the ballast tanks to displace some water.
Erm.

Please note that the amount of air needed to resurface is higher that the amount of air released during dive from the surface due the pressure difference. The difference can be so big, that it does not worth the time to wait for compressors (just vent it!).
So a submarine needs plenty of amount of highly compressed air before it can attempt to dive.
 
  • #7
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Summary:: Are there any submarines, or UUVs that don't use compressed air to sink and rise?

I have been wondering about submarines for a while, and especially their ability to sink and rise on command. I understand that they do this through ballast tanks and replacing water with compressed air, which increases the buoyancy force and helps them rise. (I understand that my knowledge is highly superficial, so if anybody feels that they can explain this better please do so :) ). However, submarines can't store an infinite amount of compressed air, so do they have a limit to the amount of dives they can do? I have never piloted a submarine myself, but I do know that many subs have dive planes. In which situations would a submarine captain use the dive planes vs. ballast tanks to rise.

Sincerely,
Richard

Edit: Do smaller UUVs have different ways of sinking and rising than larger submarines?
Analogous to airships, there are rigid airships with compressible ballonets (Zeppelins) that can set their buoyancy arbitrarily like conventional submarines, and there are 'blimps' that are always slightly-heavier than air and use power to provide the final component of lift.

Likewise you either have an adjustable buoyancy submarine or one like above that is lighter than water but uses power to descend

The question of whether they can store enough compressed air would, I think, depend on the technology. If they used a variable volume plunger-like system on the submarine, they could change their volume for the same mass, losing no mass in the transition between buoyancy levels and no requirement to take in or vent air or water (nothwithstanding leaks). No idea if such a thing has been conceived or made.
 
  • #8
Blimps are simply non-rigid airships, they are lighter than air.
Once at sea, submarines use compressed air to adjust their ballast levels for neutral buoyancy or slightly negative buoyancy, then operate by using their diving planes to ‘fly’ through the water. Since military submarines all carry air compressors, as long as they have fuel (conventional or nuclear), they can recharge their air tanks as required. And since they all have snorkels, they don’t need to surface.
As for the ‘plunger’ system suggestion, submarine interiors are kept at one atmosphere, so what happens to the air/water that the plunger displaces as it cycles?
 
  • #9
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Blimps are simply non-rigid airships, they are lighter than air.
Only unmanned tethered blimps are lighter than air.

And, no, 'rigid' airships have variable ballonet pressures. Blimps have a fixed envelope without the capacity to adjust the pressure, dynamically.

There is an obvious reason why manned blimps are made to be heavier than air ... if you are lighter than air and have an engine failure ... ooops.

As for the ‘plunger’ system suggestion, submarine interiors are kept at one atmosphere, so what happens to the air/water that the plunger displaces as it cycles?
The plunger would (have to!) act into an evacuated or gaseous cavity at the outside of the vessel. I don't understand how you think I would be suggesting that penetrates to the living space and creates a pressurised cabin!?

Yes, there would be compressed gas in this operating cavity (if not evacuated from the outset) but as the OP has requested, there would never be a need to vent ballast tanks or require some source of gas. As I described, such a system would alter the volume of the submarine and keep the mass the same, whereas a conventional submarine adjust the weight and keeps the same volume. In such a case (conventional submarine; fixed displacement, variable mass), an external source of gas is required (conventionally, periodic resurfacing). In the former case (my suggestion, to answer the OP; fixed mass, variable displacement), no external sources of gas are required.
 
  • #10
Baluncore
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There is an obvious reason why manned blimps are made to be heavier than air ... if you are lighter than air and have an engine failure ... ooops.
You can alway vent or compress a small volume of lifting gas. Compression of lifting gas from the internal bags into gas bottles was used in rigid airships like the Zeppelins to control the buoyancy.
 

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