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Saturation Submarine

Expand submarine capability using a little pressure
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Effective ocean-going submarines have been around for over a century. In the beginning, they were not pleasant places to be. Sealed in a cramped steel tube with diesel fumes, explosives and a few tons of battery acid, the crew were also subject to dreadful eating, sleeping and washing facilities. Civilized countries mitigated this privation with ample rum/gin/schnapps/torpedo polish.

Nowadays things are different. Gone are grey-skinned ghouls in wool sweaters impregnated with dirt, and a month's nervous sweat. Instead, they're swanning about with coffee machines and two pairs of shoes. Obviously, standards have slipped and they've all gone soft. At the expense of a little inconvenience and discomfort, I think we can radically increase capability.

A submarine is essentially a pressure vessel turned inside out. The latest Seawolf class of submarines use that vessel to withstand the pressure ~3000ft underwater, which is around 90 MPa. Interestingly, humans can adjust to ~1500ft depth with technique known as saturation diving, where divers bodies become saturated, or equilibrated with the special mix of gasses they're breathing. This means they can live and work for very long periods underwater without repeated and time consuming pressurizing/depressurzing cycles.

Now, in a submarine. the pressure vessel is free. Lets get the crew in and start winding up the pressure to a steady 45 MPa with a standard trimix of He, O2 and N2. What does that get us? Well, funny voices for one. But other benefits present themselves.

If the submarine could dive to 3000ft before, now the same sub can hit 4500ft.

CO2 buildup would be simple to deal with since it begins to liquify at 5 MPa and at 45 MPa you'll have to wipe it up with a towell.

Compressed air could be used as energy storage, with the sub at 45MPa, an additional vessel inside could store much higher pressures than usual, the energy density would be triple that of lead acid batteries, but only when released at the surface. Also, storage of O2 would be much more efficient.

Air cooling would be vastly more efficient, the little fan on your computer wouldn't be necessary and exotic reactor designs could be used.

The crew would be motivated to stay aboard until the end of the planned mission.

Everyone would feel about 12lb lighter due to boyency.

The pressure cooker won't need a lid.

At a specific depth you could open the bottom and have a pool.

There are some downsides, the kettle would take a long time to boil and then make an unsuitably hot cup of tea. Any TIG welding will problematic since the argon will be solid and your darts game will likely suffer.

bs0u0155, May 09 2019

Hydrox https://en.wikipedi...rox_(breathing_gas)
Saturation diving with Hydrogen [8th of 7, May 11 2019]

[link]






       Were you proposing to have an internal pressure of 45MPa even when the sub is on the surface? Only I suspect that submarines are rather like eggs - very good at resisting external pressure but not so good with internal pressure.   

       Obviously there are other ways in which submarines are like eggs (they both have an "e" and and "s" in them, for example).
MaxwellBuchanan, May 09 2019
  

       //an internal pressure of 45MPa even when the sub is on the surface? //   

       Yes, at least if that's a buildable boat. A simple steel pressure vessel will be similarly good at internal vs external pressure, so it's theoretically possible. However, I am willing to admit that submarines could be more complex than a CO2 cylinder. Certainly the way hatches are made is sensitive to the direction of the pressure gradient. Some aspects would actually be simpler, I imagine shaft seals etc would benefit from cruising around at a deph chosen for 0 delta p, the internal pressure would also mean you could replace the bilge pump with a one-way valve.   

       I imagine the mission profile would start at normal pressure and slowly increase while in friendly waters, probably a good way to check for leaks. Then the sub can tool around below everything else, and being extraordinarily hard to see. The return leg would allow plenty of time to slowly depressurize. I've not seen any depressurization schedules longer than 8 days, that fits a sub patrol nicely.
bs0u0155, May 09 2019
  

       Communication beteeen the ceew members, relyong on hand gestures?   

       I didn't think you could spend an indefinite amount of time in those fluid diving suits without going quite loopy, but I could be wrong.
RayfordSteele, May 10 2019
  

       I like it.   

       //time in those fluid diving suits without going quite loopy, //   

       No fluids. Just an oxygen helium nitrogen mix. All gas. Everyone does have a party-baloon voice though.
bs0u0155, May 10 2019
  

       The voice thing might help to prevent a nuclear war. It's very difficult to be angry - or even resolute - in a squeaky voice.
MaxwellBuchanan, May 10 2019
  

       Why not use Hydrogen instead of Helium ? It's simple, and Hydrogen can be generated directly from the surrounding eater. At very high mix ratios, combustion isn't a problem; the technology has been proven to work.
8th of 7, May 11 2019
  

       More engineering complexity, more risk due to living in a more complex and a less understood dangerous environment.   

       So really, a more pilot friendly deeper going Sealab. Deep cutting edge technology. At least, no one will be in a rush to disembark.
wjt, May 11 2019
  
      
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