Why Not Pre Pressurize Robotic Submarines?

Because the sub could not withstand the internal pressures on the surface. It would explode.

The cigar-like design withstands external pressures much better than internal pressures.

Submarines shrink by inches across, when at depth.

Someone once discussed this here. They told of tying a string across the hull and watching it sag as they dove.

I don't know about adding pressure as the sub dives, but it isn't done presently for some reason.

Building the sub to withstand charging it to more than 15,000 psi internal pressure on the surface would require more material than building it to withstand a similar external pressure when submerged. There are also problems with trying to build an even higher pressure supply tank that might be taken down with the sub to pressurize as it goes, or with building a several mile long 15,000+ psi flexible hose.

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It does seem like partial pressurization might help. They might already do that though.

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An option in unmanned subs might be filling the space with a liquid and having a piston in a cylinder communicate the outside pressure to the inside fluid.

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By the way, I've witnessed the sagging string. It has a lot to do with the fact that the sub is not circular in cross section. It it taller than it is wide. If you were to tie a string vertically when at test depth, it would be slack when you surfaced.

A simple method would be to flood the internals with an inert liquid and connect to outside environment via a diaphragm or bellows,or as you say, a cylinder with outside and inside on opposite sides of a piston.

If the fluid is incompressible,or nearly so, there will not be much displacement required to regulate pressure.

Or perhaps a flexible structure instead of rigid,like a GelCap medicine pill?

Living organisms thrive in the deepest oceans,and are flexible.

I remember seeing many years ago a fluid that could carry enough oxgen to allow breathing it instead of air,but don't recall the name of it now.It was totally non-reactive to virtually anything.They showed a mouse breathing it with no problem.

I heard that the Navy was using it for extreme dives.

Anyone else heard of this?

Perfluorocarbons can be used for this. Remember The Abyss?

I'm not up on this any more, technically, but it is/has been explored for some years now.

I first heard of this in 1983, while working in the aerospace industry.

We designed and built electronic circuitry for deep submergence military evaluations. They reported back that while the concept worked, very strict control must be kept to eliminate internal gas bubbles that would not support the pressure. Also, virtual leaks during decompression will cause explosions. Nasty possibilities. These things have actually occurred on tactical vessels.

'...Also, virtual leaks during decompression will cause explosions...'

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er....what? Do virtual leak cause virtual explosions, or tangible physical explosions?

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All kidding aside, if you could elaborate some on this, it might be very enlightening.

A virtual leak is a leak that is not connected to the main pressure source, but is never-the-less connected to a port. Like a balloon within a cavity. The balloon is connected to the outside world as is the cavity. They are not, however connected to each other. Obviously, the cavity can explode when pressure limits are exceeded, and the virtual leak can do the same thing.

The major problem,however is that pressure vessels are designed to be pressurized in compression only. If the same pressure were to be applied internally the pressure vessel would explode. Your assignment is to design a pressure chamber capable of withstanding both external and internal pressure. When you have accomplished that task, your idea will work great.

My idea?

I think that mouse thing came from the movie "The Abyss".

TINAC has some good ideas regarding this.

I can't help but think, however, filling the submersible with a non-compressible fluid is so obvious, there must be a problem with this design.

Actually the mouse thing is good science. Perfluorocarbons have a relatively high solubility for oxygen. They cannot be infused into the bloodstream as a substitute for blood transfusion, but there was interest in the late 80s for developing emulsions which could be used. That faded out, but clinical interest remained in partial liquid ventilation for the infant respiratory distress syndrome. In IRDS the lung is lacking in surfactant, which normally helps to keep the lung open by lowering the surface tension. Filling the lung with perfluorocarbon, across which the oxygen passes readily, is a good way of keeping the infant lung open.
The mouse can breathe spontaneously when submerged in oxygenated perfluorocarbon, he adult human has too long a path for the oxygen to travel for this to work.

I recall something like this- was it a fluorinated hydrocarbon fluid?

I did read a welding article on Wood's Hole building one of these. There could be more to the situation than simply the pressure crushing an air filled chamber. Any more details available?

It wouldn't float.....it has to maintain buoyancy...

Lower specific gravity (below 1.0) fluids would be required.

As I understand it though, these are often much more of a framework than the conventional type of submarine, and buoyancy should be roughly neutral anyways (depending on ballast etc.).

It is true that perfluorocarbons are chemically inert, but so are many other fluids. Their almost unique property of being able to carry oxygen in solution is not terribly relevant here.
Silicone fluids are inert and more environmentally friendly.

The Nereus was a purpose build vehicle for extreme depth and pressure... It was made of ceramic instead of steel and was filled with precisely designed ceramic spheres rather than the much heavier syntactic foam that is typically used for submersible vehicles. Each hull contains between 700 and 800 9-cm (3.5-inch) hollow spheres that are specifically designed to handle intense pressure.....

http://www.whoi.edu/cms/files/FloatingWithoutImploding_68272.pdf

http://en.wikipedia.org/wiki/Nereus_(underwater_vehicle)

http://www.whoi.edu/page.do?pid=10076

"Pieces of the craft were discovered floating on the ocean surface near the dive site, confirming a catastrophic failure"

• CNET
• Sci-Tech

when driving do you hit the brakes in anticipation of stopping or only apply them when you need to stop?

From reading the wiki article, there are 2000 lithium-ion batteries for power. I don't know if these can be designed to operate at 11,000 meters (36,000 ft), pressure depth.

The circuit cards that are manufactured at 'sea level' pressures, may have small air bubbles that could stress the board at those pressure depths. As well 'hermetic' electronic packages that can't support those pressures.

Someone did update the article indicating it was lost May 10, 2014.

Another reason is because the sealing O-rings need to be properly seated prior to use. These are designed for either inner pressure or outer pressure, and leak slightly (at sea-level pressures) when taken from one to the other. At those depths, such movement could be fatal.

I worked with mini ROVs: one type was designed for up to 10m depth, and was pressurised before use, but leaked if used at a depth greater than the pre-pressure due to the movement of the O-rings.

Another type was designed for 300m depth. It had a partial vacuum applied after service, which 'pulled' the O-rings into place: a much more reliable result.

Certain components were designed for much greater depths: a pan-and-tilt unit for camera & lights was designed for 1500m depth. It was oil-filled.

So when they are oil filled, are you privy to what typically is the factor that limits depths; to 1500m in the case you describe?

Design of the outer casing.

Under the pressures found at those depths, there will still be some deformation of the unit, so a thicker wall or stronger material would be required.

Or the test rig was only capable of producing pressures to mimic 1700m or so without damage, therefore 1500m is as far as the warranty will permit. (I say this as I have seen identical designs with deeper ratings several months later)

Seems like the purpose of using oil would be to communicate, at least partially, the ambient pressure to the interior and thereby negate or significantly reduce stress that would otherwise make the casing fail.

To put some numbers into this, the MH370 aircraft is believed to be at a depth of around 15,000 feet, equivalent to a pressure of 6,680 psi. If the sub were to be pressurised from a cylinder/tank of 1/10 of the internal volume of the craft, it would need a filling pressure of up to 70,000 psi. I leave it to the experts to design and manufacture the compressor and the cylinder to be filled, given that a commercial diving cylinder may be rated for 4,400 psi.

Consider putting the compressor on the ship, not a tank carrying the pressure from an on shore location.

I realize it would take a while to do it,with cooling stops in between stages, as in filling scuba tanks,but it usually takes a while to get to the dive site anyway.

Even at 4400 psi, that is half the normal differential pressure that would normally be encountered.

Of course,as others have pointed out,this may not be feasible for other reasons besides the hull integrity,such as the sensor and control chips, etc.

Of course,magnetic coupling thru the bulkhead to drive the mechanical parts may be feasible,making bulkhead seals unnecessary except for stationary seals,instead of rotary seals,which are harder to design.

Tapered profile(wedge) O rings with variable durometer scales,or stages, could be implemented for compression type seals to adjust for varying pressures.

Pressures are awfully high. Spheres are awfully strong. William Beebe went as far down as you get in a sphere. (not bad for a bird watcher by trade!) He had a lot of time to think on his first dive, and he realized that the cable was VERY heavy, and might break, so the second sphere was ballasted with steel ball bearings held in place by electromagnets so if his power supply failed he would have half a chance. His third was held up with a gasoline filled metal derigible.

So if you have some electronic equipment which can't stand the pressure, why not just pack it into a sphere, and go anywhere? Bottom of the ocean is fine! Personally, I kind of like the idea of loading the sphere is perflorocarbons, but it may simply not be necessary. It might add too much of a complication. Heck, I know my computers last longer if I don't shut them off, and THAT (potential) damage is done by copper runs flexing and changing due to temperature changes. Imagine how they could fail with pressure changes as well!

Just my 2 cents, I didn't say anything that has not been said by better people than I! I just love the idea of boldly going where no man has gone before!

the problem is likely because the flotation spheres were ceramic. ceramic doesn't fail gracefully, when it fails, it fails catastrophically.

I would imagine that anything that failed at that differential pressure would be

catastrophic.

Even a coating of Polyol,which can contain a TNT explosion,would probably

fail in a violent way.

Perhaps a Polyol coating would hold everything together so that it could be retrieved

in one piece for failure anaylsis?

A coating sealing the whole exterior,with recovery like a broken egg in a sack?

I presume that since they had fiber cable,the last instant of communication was

recorded for any possible analysis.

It would be interesting to see that,in freeze frame,just for curiosity.

But the whole purpose of my original post was to explore ways to reduce the

differential pressure to achieve a safer dive.

Feedback from this group of great people has led me to see potential problems that

would not have occured to me otherwise.

I will have to give it much more thought.

Thanks to everyone!

Ever tried to break an egg by simply squeezing it in your fingers? Surprisingly strong! And look how thin the shell is.

Now half of CR4 is going to break some eggs in a pan by squeezing them! Good!

TRUE!!

LOL!!

The feat is more impressive in its difficulty if you specify squeezing the ends of the longest dimension. Eggs break really easily if you squeeze points across the center at a short dimension.

Your point still stands, water 'squeezes' fairly uniformly.

Inquiring minds want to know how you found that out!

Mr Harris 7th grade science coach.

A few facts about eggs, gleaned from my pressure experiments:

They are harder to break lengthwise than crosswise,however,if you persist in the lengthwise direction with much vigor,they will break.

Egg makes a lot of suds when washing it out of your hair.(There may be a potential here for a shampoo!)

It takes about 6 paper towels to get the egg off of the cabinets and counter tops,but only 2 to get if off of your face and hands.

Rinsing is required to prevent puckering of face when the egg dries.

Raw egg white has no taste,but the yolk does.

The shells are gritty and tend to cling to teeth.

Notes to self:

1. Enclose egg in zip lock bag for next experiment.

2. Do not grimmace when exerting maximum pressure.

3. Do not conduct testing when wife is at home.

4. Rolling pins make large knots,but not as severe as cast iron skillet,which tends to break skin.

5.My wife has a really good throwing arm.

Thanks for that.

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A side note... I'm not the type to use hand sanitizer and I'm certainly not a germaphobe, but it is a good idea to wash eggs with soap or detergent an water if there is a likelihood that raw egg and/or shell is likely to get in your mouth, nose and or eyes.

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Salmonella, among other undesirables, is not rare in chicken production....and eggs come out of a cloaca.

The hazards from raw chicken do not come from the chicken itself,rather from the mass production methods of processing.

They use the same water for rinsing hundreds of chickens,some of which are contaminated with feces.This insures that all are equally contaminated.

Growing up on the farm,free range chickens,as well a ducks, geese,Guineas and Bronze turkeys were the norm,and raw eggs,from all of the birds were eaten daily with no problem,however,I found the duck eggs were a little too strong for my taste,but mom made great cakes with them.

Our wrestling coach asked us to eat raw eggs and milk to build muscle.

I could slice the end of of an egg with one swift swipe of the knife without spilling a drop.Then it was down the hatch in one swallow,followed by a glass of unpastuerized,unhomogenized milk.

(You must slice off the large end,but not below the air pocket)

One could make egg nog at Christmas with raw eggs,no problem.

When we cleaned chickens at home, we were very careful not to contaminate the meat with the intestines,and we did not have to cook the chicken till it was tough as leather to be safe.

Ever wonder why you can eat wild duck rare?

Some modern food processing methods are killing us.

You are right about the hazards with chicken being in the production, which is why I specified 'chicken production'.

You can still make eggnog, and drink raw eggs, it is just a good idea to wash the eggs, because the cloaca is the everything hole. You can avoid contaminating the meat with the intestines.... but the eggs come out at the same place.... right?

I have a brother that will not eat liver because it is an internal organ.

I asked him why,and he replied "Do you know where that comes from?"

"Sure" I replied."But you eat eggs,don't you?"

"Of course" he replied.

"Do you know where they come from?"

Now he won't eat eggs.

LOL!!!

Maybe he'll start eating liver again if you remind him that it is in fact converted to an external organ by the time human consumption begins.

Good advice.

Raw eggs here in Europe mostly have Salmonella both in and on fresh eggs. I avoid using/making things with eggs that don't get "cooked"...also Frequent hand washing during cooking/preparing is a must....

This is why companies who make Mayo do not use fresh eggs, they buy in a dried Version that has no bacteria of any sort. How that is achieved someone else will know. I don't ...

We are what we eat,and by extension, we are what we eat eats.

They are now using chicken house litter to feed cattle.

In rancher's eyes,cellulose is cellulose,whether from hay or sawdust.

Chicken house litter has enough ammonia in it to feed the digesting bacteria in the sawdust.

They compost it until it reaches 160 degrees,then feed it to the cows.

They mix a litte supplement with it with vitamins,antibiotics,and growth hormones.

YUM YUM!!

No wonder it is hard to find a good steak.

I hope these modern methods do not make it to Europe.

Small wonder our country (USA) is turning to S-it! (we are what we eat).

O.M.G.

Say it isn't true, PLEASE?

There have been numerous attempts to farm/ranch combinations of crops and livestock that minimize input and waste.

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One that comes to mind is corn/hog/alligator. The corn was grown to feed to the hogs, any hogs that could not be sold....disease, lightning, whatever, became alligator food, and the alligator moat water and pig run off fertilized the corn. I don't know of any farms like that today, so it must not have been the game changing success that was initially envisioned.

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Thinking about a cow forced to eat chicken feces isn't pleasant, and does make you wonder if it changes the flavor of the meat. Additionally unsettling is that chicken feces isn't the only poop supplementing the diet of cows. Cows are fed their own feces as well.

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just as you come to terms with that, _{possibly making use of some mouthwash to dispel the lingering taste of vomiting just a little bit into the back of your mouth at the previous thought,} I'm going to suggest something that most will probably find outlandish, initially... the idea isn't completely deranged/horrible/wrong.

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Coprophagia is revolting to me personally and to most people, but for animals that are not people, the reaction is often less stark, and very often doesn't even run in the same direction. The dung beetle is a bit too far to elicit any nods of agreement. Far more common, everyday examples abound.

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After kittens are born, for quite a while, not just initially, the mother cat dutifully eats kitten excrement until they learn to poop in the right place. That is admittedly still a very special situation.

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Most people who have had their dogs around horses for the first time have been faced with watching that cute face, that many find smoochily irresistible, horking down green biscuits freshing emerging from beneath a horses lifted tail.

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Fish are breathing and many are eating fish excrement nearly without cease. Worms may be eating some excrement, and we often encourage animals that we eat to consume worms....feeding worms to chickens, and fishing with worms.

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We humans don't even abstain completely from the unholy garden of pooply enticements. While I have never even come close to eating chitlins or drinking a brew of kopi luwak, I am fond of some sausages which come in skins, that while well washed, are about as close as you get.... I will also eat boiled shrimp without deveining.... and that isn't really a 'vein'.

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Most importantly, it is very common for us not just to tolerate cow manure in the soil we grow our tomatoes, squash, broccoli, and other foods, but it is often sought after. Many people claim food grown in cow manure tastes better than if refined fertilizer was used instead.

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When we eat mushrooms grown in cow manure, the mass of that mushroom largely came from the cow manure. We seem to be fine as long as there is at least one organism processing the poop before we eat it.

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The idea of feeding excrement to cows might be more than reasonable, it might be important.

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Getting a calorie of beef to the table has been estimated to require several hundred or several thousand calories. Feeding the animal that is growing the meat, is no small expense in dollars, land, or resources, and poultry and cows aren't particularly efficient at extracting all the available nutrition. Useful proteins alone make up around 25% of chicken poop dry matter, and around 12% of cow manure dry matter.

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So supplementing cow and chicken feed with recycled nutrition, reduces the demand on resources created by the luxury of eating meat, but that isn't even half the benefit.

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One of the problems with large industrial meat farms is the waste run off. Not only is nutrition being wasted, but in the forms it exits, it be a significant burden on local and not so local ecosystems.

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In the end, there is a way to do this safely for great benefit. I don't know if that is exactly what is occurring, but the idea itself is not as bad as it appears at first blush.

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Cow manure didn't make your tomatoes unpalatable, or the carrots, or the squash, or the mushrooms.

I think it was probably a good post, but my stomache would not take it. After 1/3rd I stopped reading.....sorry......apologies too. My bad.

I understand. I should have been more tactful. It is an important topic, because large farms are often a huge burden on the surrounding environment and significant users of resources.

Very true.....

Eating grass fed, well raised beef and dairy products makes a lot of sense. I'd certainly feel a lot safer trusting they types of things you choose to eat than they types of things large corporations would choose to feed me.

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Conversion to more readily digestible, more palatable, and longer lasting feed has been around as silage for quite a while, though I'm ignorant to when it began. Well made silage not only makes calories available that weren't necessarily before, even though some of the total energy is used in the conversion process. It is also easier to digest and can increase appetite.

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Part of the increase appetite might have to do with cows enjoying being inebriated.....calling it cow-beer would have some merit.

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By the way, I'm marking these as 'not off topic' in the sense that I'm not going to submit something that I believe is the opposite of a 'good answer'....especially not 5x not a 'good answer'. Anyway this is all in the context of pre-pressurizing robotic submarines, right? ....and what better gas to pre-pressurize with than cow farts, grass-fed of course.

None the less, I appreciate your honesty about what you might see as deficiency in my own.

Lol!!!

I was on the edge of a project that did just that back in the late 70's, but only to a few hundred meters depth.

The sub was made from a large propane cylinder - well able to withstand pressure - but the internal pressurization was from dry compressed gas (CO2 or N, I forget). This made life a lot easier on the glands and seals to the exterior.

Internal pressure was automatically maintained at +1 to 5 psi relative to the outside IIRC so that minor leaks were of gas out not water in.

Lots of other clever designs went into that sub but I won't bore you with them!

In many cases they are, but there are some components that simply cannot withstand the pressure and those have to be in pressure vessels to protect them. things like batteries and aluminum electrolytics and metal can semiconductors for instance simply cant take any appreciable ambient pressure. pressure balancing is actually quite simple. put the components that can withstand pressure in a container, fill it with oil (typically the same hydraulic oil used for the hydraulic system, and it is part of the supply tank plumbing, it also helps with heat removal.) and put a flange with a rubber diaphragm accross it. that way the external pressure and the internal pressure remain the same.

If all the components inside the sub can withstand the presures you are proposing, you don't need a pressure hull in the first place!!! Obviously

The pressure hull is there to protect all those (relatively) delicate components that make up ANY sub.........

What many also forget is that the pressure hull in compression can withstand significantly higher pressures than when inflated....if correctly designed that is, which we assume that it is.....

For example, in some metal crafts, observation windows for video, are cone shaped so that they are forced deeper into the seals as the pressure on them increases.

Your idea has very little merit in the real world that we live in, sorry! It has never been used to the pressures you are talking about as far as I can tell.....maybe a few PSI to check for leaks before going deep, or to set seals.....or both.

If all the components inside the sub can withstand the presures you are proposing, you don't need a pressure hull in the first place!!! Obviously That is a method already in usage, with all delicate parts in ceramic "balls", but this basically means many pressure hulls, instead of one!!!

The pressure hull is there to protect all those (relatively) delicate components that make up ANY sub.........

What many also forget is that the pressure hull in compression can withstand significantly higher pressures than when inflated....if correctly designed that is, which we assume that it is.....

For example, in some metal crafts, observation windows for video, are cone shaped so that they are forced deeper into the seals as the pressure on them increases.

Your idea has very little merit in the real world that we live in, sorry! It has never been used to the pressures you are talking about as far as I can tell.....maybe a few PSI to check for leaks before going deep, or to set seals.....or both.

I thought the hull was to protect the contents from the ocean salt water,which is

corrosive and conductive,which would corrode and destroy electronic components.

I thought the ceramic balls mentioned were for added bouyancy.

Silly me!

I thought maybe some things could stand compressed gas or inert fluid better

than salt water.

The observation windows are only required if there are occupants inside,which is not

the case for a robotic sub,but I understand the principle,which is why I mentioned

tapered o rings previously.

Also previously stated,if only pressurised to a portion of the depth pressure, it

would increase range depth by that fraction.

I think 3D printing technology will advance to the point that one day a structure can

be built that will effortlessly endure the extreme environment of the ocean bottom.

But I guess that too is just silly speculation.

No, its a perfectly valid speculation. Just most engineers are VERY conservative, and prefer tried and proven technology over the opposite. As do you. And I. We know what pressure is in the abyss, and even the trenches. A man sized sphere went there before, and can go again. Smaller spheres would be simpler, and easier to make. That is the tried and proven technology. Personally, nitrogen or argon would be good "fillers" because they are very dry. I can't predict what perflorocarbons or oil used as a "filler" would do to my computer components. If they are perfectly harmless, then I would still not trust them because there is air in all sorts of places...even inside microchips. That is why I suggested the tried and proven technology of an air filled sphere at 14 PSI absolute. Ceramic....steel....titanium....all good. I think anything which would break a ceramic sphere would dent and result in the collapse any other material. I dunno. Would have to do a lot of experiments with a long cable and progressively lighter gauge spheres.

One thing to keep in mind- and doubtless one of the reasons for using spheres instead of ovoids such as an egg shape- is that this pressure is a continuous, non-localized load.

So dents aren't likely, unless the objects aren't properly secured and bang against something that causes them or else there is a structural flaw that allows one area to deflect at a greater rate than others. Either of these would seem very likely to cause catastrophic failure at these pressures!

As a note to your comment on breaking eggs- I'd be very interested to know what it takes to break a raw egg, if it was placed in a sealed container and subjected to hydraulic pressure. Anyone ever tried ?

Eggs do have an air pocket, so I'm guessing the pressure it can withstand without cracking probably won't be phenomenally high.

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A long time ago, I did attempt to scramble an egg, or at least break the yoke, without breaking/piercing the shell. Neither very vigorous shaking, not placing the egg into the extremely painful spot in an ultrasonic humidifier was successful.

You have to be very careful with titanium at extreme depth. Many titanium alloys get increasingly brittle with time at depth due to hydrogen embrittlement.

There are probably a few types of steel that exhibit similar behavior at extreme depth.

this is true, but if you have proper galvanic protection this isn't that much of a problem.

The hydrogen isn't being introduced electrochemically, it is diffusing interstitially at great pressure.

If you know for a fact that galvanic protection is adequate for titanium at depth in the ocean, I'd really like to read up, if you know off any references you could link.

where would the free hydrogen be coming from if not electrochemically generated? the problem is that galvanic protection for steel generated hydrogen in titanium, but if titanium is electrically isolated than that is not an issue.

https://www.onepetro.org/conference-paper/NACE-96554

I'm possibly on weak ground here, but my recollection here is that at extreme pressure diffusion of hydrogen into titanium can occur at relatively cold temperatures in a similar way as it does at normal pressures and very high temperatures.

Atomic hydrogen is present, even if momentarily in abundance, from things like small reactions after small scratches in protective oxidation layer, but also in the fleeting phases of normal dissociation of water. Even hydronium isn't really hanging onto that last proton all that hard, certainly not like the other two. Typically it ends up on the outside of a large cluster and much more available to be mobile.

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Once again, going on memories from long ago, I believe Soviet subs had to calculate ever decreasing max allowable depths based on the previous times at various depths, the deeper and longer they were down, the larger the reduction in future dives.

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I'll look for some documentation in a little while. Thanks for the reference, I wish I were ready with one myself right, and honestly I am a little rosy cheeked at realizing with how much certainty I proclaimed on something I haven't looked at in a very long time. Anyway, we'll see.

The deep water drilling and production industry uses Titanium for permenantly installed equipment and drilling risers in depths exceeding 10k feet on a routine basis. So there has to be issues of galvanic polarization in the soviet subs.

I'm convinced you are right, and that I have had this idea that seems fairly strange in retrospect, floating around in my head for decades now.

Thank you, for the help.

I would doubt that the ceramic spheres collapsed,more likely the hull itself collapsed instead.

You make a good point about micro-cavities in chips,I hadn't thought about that,but I don't see that as an insurmountable problem.

Expensive,perhaps,but when has money ever stood in the way of a government project?

Thanks for putting a new wrinkle in my grey matter.

for ROV's the pressure vessel is to protect the electronics from pressure. the pressure balanced vessel is to keep salt water out of electronics that can otherwise withstand the pressure and to act as (part of) the hydraulic supply tank. otherwise there is no "hull", just the structure that holds all the bits together.

Sacasm is the humor of the intelligent,and is lost,ironically, on those that need it the most.

You need to understand better about sarcasm. I was not being sarcastic, only factual.....

Have a great day anyway!!

The sarcasm was in post#30,but you obviously did not get it.

I still like your beuatiful dog.

Have a great day also!

I had to laugh, thats sarcasm???

Wow!!

You don't have to read it thru twice if I write it!!! It obvious Form the first read!!!

Mother nature has had hundreds of millions of years to handle this problem, and has succeeded.
There are living organisms on the sea floor in the deepest trenches on earth.
Biomimicry holds the key to the depths.
A flexible,protein based structure will ultimately be the way we will conquer the ocean.
Flexible electronics are in their infancy right now, but look how far we have come since the Wright brothers.
Another 50 years,and we will be touring the Marianas trench like tourists to the Grand Canyon.
High definition video is already being sent wirelessly through the water by the military.
Cavitation of the transponder used to be the frequency limit of underwater
communications, but a new method using Lasers to generate sound at high def
frequencies has been developed and is being used by the military to send video
underwater.
This means no tether on the ROV's for communication and control.
There are other challenges that will crop up as development proceeds,but they will be conquered in due time.

'...Mother nature has had hundreds of millions of years to handle this problem, and has succeeded....'

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There is the possibility that things began down there with chemosynthesis, and the problem Mother nature worked out in a few hundred million years was how to deal with the absence of all the pressure up here.

Mother Nature is good, but not that good. Creatures which have evolved at depth cannot survive near the surface, and creatures living near the surface have a depth limit.

Octopi have been seen in the deepest parts of the ocean,as well as shallow water.

Probably of slightly different types......I saw a great program recently on Giant Squid.....Octopi were also shown of different type to the shallow water types.....

Here is an interesting artcle describing the differences, even life spans are different, between the shallow and the deep Octopi.....I hope this helps.

Deep Water Octopus

Everything has a depth limit.... the swimming ones don't max out lower than the deepest accessible ocean floor.

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Joking aside, there are a number of marine animals that survive very large vertical ranges.

In the marine mammal category, beaked whales are thought to be the diving kings, recently recorded on dives almost two miles deep.

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But there are likely much smaller forms of life that have no problem adjusting to far greater pressure changes. Tardigrades, AKA moss piglets, are a good example.

While one could pressurize the sub at the surface or at depth, isn't the reason for an internal void to allow equipment/instruments etc. to operate at surface atmospheric pressures i.e. to protect them from extreme pressures?

This being the case, it would be pointless to pressurize.

With a few exceptions, as noted by others,such as internal voids within integrated

circuits,etc.,I don't believe that pressure,per se, is the problem,but rather differential pressure.

I believe the IC cavity problem could be overcome easily,especially since diamond is set to be a replacement for silicon in the near future.

As long as the pressure is the same on the inside and outside of the vessel,there would be no hull stress.

Sensitive devices could still be encapsulated in small spheres,which are stonger than large ones.

The hull would contain an inert medium to prevent corrosion and enhance cooling of components.

Some differential pressure could be tolerated, within known technological limits.

Many proteins are stronger than steel,and carbon nanofibers are even stronger,almost indestructible.

Flexible electronics are in their infancy,but I see a great future ahead for them.

We are currently in the "Wright Brothers era "of ocean exploration,relatively speaking.

We know more about the moon than our own ocean,but that will eventually change,(I hope).

Elaborating a little further on the future of submersibles created by 3D printing, a torroid shape may be the winning configuration.

A high pressure torroid is presently very difficult to manufacture because of the uneven stresses between the inner and outer diameter,and the need to make the inner shell thicker and taper it to the thinner outer shell.

3D printing could eliminate this problem by creating a thicker inner diameter shell,and tapering the thickness of the shell as it moves outward,and a seamless joint.

Internal gussets could be incorporated during printing.

This would allow high pressure precharge of the torroid,with stresses decreasing as depth increased.

No end caps or longitudinal stresses to worry about.

Just a wild thought........

A high pressure torroid is presently very difficult to manufacture because it doesn't exist. Try using your spell checker or look up toroid.

You got me on that one.Funny the spell checker didn't catch it.

Just so you know, a torroid is redneck medical term for a torn hemorrhoid.

Thank you for the laugh.