Indonesian Submarine

I don't see that as being a likely scenario, unless the sub had lost power...or rudder control, or hit an obstacle, had an onboard explosion or environmental system failure....

Depth is at 839 meters...

Submarines don't go below about 300 meters....normal cruising depth would be somewhat less than that...

Stop look at me, I didn't do it!

Ah Ha! our first suspect....take him to the torture ch,,,er ah, interrogation room....

What about this? A 1966 study by the U.S. Navy noted that "The passage of large-amplitude internal waves could make submarine depth control difficult, particularly when the submarine is running quietly at low speed." The report, titled Internal Waves: Their Influence Upon Naval Operations, added that such waves "could initiate uncontrollable sinking of a submarine."

...."Perturbations caused by the internal wave could initiate uncontrollable sinking of a submarine without power if the submarine were more compressible than sea water."....

..."water travel in elliptical orbits, and (2) energy travels at the group velocity. The maximum amplitude of the internal wave disturbance occurs at or near the pycnocline, and only small amplitude variations occur at the ocean surface."...

...."There are two ways in which the wave could affect a submarine's depth. One is by changing the buoyancy of the vessel if the water temperature and density should suddenly change.

A sudden temperature change of 5.0 C would be considered large under normal circumstances, for it causes the density of sea water to change by about 0.1%. As a submarine is nearly neutrally buoyant, its total average density is about 1 gm/cm . The buoyant force (positive or negative) exerted on a vessel as a result of a 5.0 C temperature change would thus be about 1 dyne/cm^, giving the vessel an acceleration of approximately 1 cm/sec^, neglecting drag.

A submarine under way could easily correct for the effect; however, this slight acceleration could cause serious problems for a submarine without power, hovering, or moving at very slow speeds. Under these conditions it would not be possible to trim the vessel by the diving planes alone. It would be necessary to blow ballast, a difficult process during power failure and undesirable during quiet running.

If the vessel were more compressible than sea water, the acceleration would be accentuated as the vessel's density responded to changes in hydrostatic pressure. Vertical displacement could thus reach serious proportions unless promptly controlled.

As the vessel reached thermal equilibrium with its new environment, its buoyancy would change in the direction tending to restore the original position and would thus have a damping effect on the influence of the internal wave."...

https://apps.dtic.mil/dtic/tr/fulltext/u2/632010.pdf

So the way I see this as possible would be if the sub was operating near lower limit depth, and lost power, and at the same time there was a seismic event of sufficient force to amplify the internal wave, then the boat might not be able to correct fast enough to avoid being lost....

Then again it could have been a defective superstructure or crack in the hull....

https://www.solico.nl/composite-news/composite-submarine-superstructure-1

Just a wild guess... Maybe the first wave was bringing them up and they compensated just in time for the following downdraft to take them down below crush depth.

https://www.abc.net.au/news/science/2021-05-01/indonesian-sunken-submarine-internal-waves-what-do-we-know/100107196

"When a number of these waves come together, they can create a one-off perfect storm wave," Dr Corney said.

There's any number of things that could have happened, an unfortunate series of events is most likely...this was a 40 year old boat...they were doing routine testing it said, that means looking for trouble...

I may be cynical in a tragic situation, but that sounds like a 'nobody to blame' scenario. The rogue wave explanation may be possible, but it's hard to see how we will ever know.

Is there a data recorder(Black box) on the Subs?

Yes I think all large ships have a Voyage Data Recorder (VDR)...certainly all military ships....

https://workshipsolutions.com/ship-voyage-data-recorder-vdr-analysis-services-a-must-for-shipping-companies/

I was unaware, until now, about wave formation underwater and how they are formed from changes in water density. Knowing this now makes be wonder if there could be an analogy to the formation of rogue waves on the surface of the ocean? It would seem the mathematics involved would be the same and it would be possible to experience a more serious underwater wave similar to a rogue wave that could have an unanticipated affect on the sub.

None-the-less very interesting!

Changing the subject slightly (OK quite a lot), could setations be trained to locate sunken sea vessels and crashed air vessels. If the trained animals could communicate with their wild "friends", then it's almost certain that some would be aware of unusual happenings, and, they can communicate over huge distances.

Yeah, I think we'll have to do a neural implant.....

Let's hope it doesn't all go horribly wrong...

When a submarine passes a certain depth the external pressure becomes to great for the pumps to overcome,so it becomes impossible to dump the water and regain buoyancy.

Likewise,if pumps failed,or the power to them failed,disaster is imminent.

I do not know the design of the sub in question,but a common mode failure of the pumps seems likely,if they were not separately and independently supplied by power.

If they were diving and had a pump failure,their fate is sealed.

The world waits for the results from the Data Recorder.

The newest diesel powered subs are much advanced over previous generations,in performance and silence.

They are not detectable by sound alone,and with sound absorbent coating, harder to detect with sonar as well.

They can stay underwater much longer than previuos subs by using Argon and Oxygen to power the diesels.

The Argon is recycled by a scrubber.

Sea water does not dissolve Argon,and most of it is recovered.

They only need a sufficient supply of oxygen to remain under for months at the time,almost nuclear in that respect,and much more affordable than a nuke sub,so small countries can afford to buy them.

That,combined with SHKVAL-type torpedoes makes the ocean more dangerous than ever.

https://en.wikipedia.org/wiki/VA-111_Shkval

Similarly, not knowing the design details of this vessel, but in many designs, high pressure air is blown into the freeboard ballast tanks to cause the vessel to surface.

https://maritime.org/doc/fleetsub/air/chap1.htm

https://en.wikipedia.org/wiki/Emergency_main_ballast_tank_blow

Pumps are generally used for fine tuning the trim.

https://maritime.org/doc/fleetsub/trim/chap2.htm

..."Unlike a ship, a submarine can control its buoyancy, thus allowing it to sink and surface at will. To control its buoyancy, the submarine has ballast tanks and auxiliary, or trim tanks, that can be alternately filled with water or air. When the submarine is on the surface, the ballast tanks are filled with air and the submarine's overall density is less than that of the surrounding water. As the submarine dives, the ballast tanks are flooded with water and the air in the ballast tanks is vented from the submarine until its overall density is greater than the surrounding water and the submarine begins to sink (negative buoyancy). A supply of compressed air is maintained aboard the submarine in air flasks for life support and for use with the ballast tanks.

To keep the submarine level at any set depth, the submarine maintains a balance of air and water in the trim tanks so that its overall density is equal to the surrounding water (neutral buoyancy). When the submarine reaches its cruising depth, the hydroplanes are leveled so that the submarine travels level through the water. Water is also forced between the bow and stern trim tanks to keep the sub level. The submarine can steer in the water by using the tail rudder to turn starboard (right) or port (left) and the hydroplanes to control the fore-aft angle of the submarine.

When the submarine surfaces, compressed air flows from the air flasks into the ballast tanks and the water is forced out of the submarine until its overall density is less than the surrounding water (positive buoyancy) and the submarine rises.

Pressure hull

The pressure of water pushing inward is the biggest problem for anyone who wants to go deep beneath the ocean surface. Even with scuba tanks, we can dive only so far because the immense pressure soon makes it impossible to breath. At a depth of 600m (2000ft), the maximum depth subs ever dive to, the water pressure is over 60 times greater than it is at the surface! The hull of a standard ship is the metal outside that keeps the water out. Most submarines have two hulls, one inside the other, to help them survive. The outer hull is waterproof, while the inner one (called the pressure hull) is much stronger and resistant to immense water pressure. The strongest submarines have hulls made from tough steel or titanium.

Ballast tanks

There are spaces in between the two hulls that can be filled with either air or water. These are called the ballast tanks. When they are filled with air, the submarine rises to the surface; with water inside the tanks, the sub sinks towards the seabed. By changing the amount of water or air in the tanks, the submarine alters its buoyancy so it can move close to the surface or deeper down. The tanks at the front (known as the front trim tanks) are usually filled with water or air first, so the submarine's front (bow) falls or rises before its rear (stern).

https://www.quora.com/How-do-submarines-maintain-pressure

So as we can see here the submarine controls its depth by use of air and water to increase its density(adding water-going deeper) or decrease its density reducing water(increasing buoyancy)...now if a submarine found itself being forced down deeper in the water with the density of the water increasing and it was nearing crush depth, without power to steer the boat up, then they can attempt to ride it out hoping the effect was temporary and the boat would return to its original depth before hull failure, or they might blow ballast in an attempt to counter the downward force avoiding crush depth....however by decreasing the density of the submarine they are taking a chance that the increasing disparity of external and internal pressures may lead to pressure hull failure if depth is maintained artificially, ie; downward force of internal wave..or the density of the water may increase so quickly that they just wouldn't have time to react....and up and down motion would demand density of the submarine to match to maintain equilibrium, so the sub could go up and down in depth, uncontrollably....

Age may have been a factor ...most sub designs I've heard of are retired after 30 years of service...

..."Submarine hull life is estimated by submergence cycles, each time a submarine submerges and goes deep it shortens its hull life. Exceeding test depth dramatically reduces hull life, it then becomes a matter of it being economical to keep the submarine active. Submarines actually have several significant depth numbers, test depth, the depth that a is submarine expected to operationally achieve without any ill effects, when testing and certifying submarine systems exposed to sea pressure it is to this pressure that systems are tested to. So test depth is the pressure that the submarine is tested to. Then is design depth, that is the depth that the submarine has been designed to be able to reach. Next is crush depth this is the depth that it is calculated that the submarine structure and mechanical systems will begin to fail and the submarine be crushed. "....

https://www.quora.com/What-happens-to-a-submarine-when-it-goes-beyond-its-maximum-depth

Some seem to be going well beyond 30 years these days.

https://en.wikipedia.org/wiki/USS_Providence_(SSN-719)

The Boomers are going for 42 years. The skippers on those boats are going to be younger than the vessel they command.

https://www.aspistrategist.org.au/just-how-long-can-submarines-remain-operational/

Fully understanding the designs and limitations of these submarines are allowing the services to confidently extend the service life which is also good for the taxpayer too.

I would assume that past a certain age the test depth is derated for less demanding service...I guess you can just keep going until the sub can no longer be fully submerged ... similar incident here....

https://phys.org/news/2018-11-argentine-submarine-year.html

That might be the case with some navies, but from what I can tell, the U.S. Navy decommissions the vessel when the pressure hull reaches its end-of-life. De-graded capability is not a good way to operate, but for countries with limited means, they may not have much choice.

"Questions are being raised as Indonesian authorities try to shed light on the Southeast Asian nation’s first submarine disappearance. According to the Janes analyst, the incident could have been avoided if the vessel wasn’t overloaded or kept in service for so long.

The typical life cycle for a naval submarine is only about 30 to 35 years, Ridzwan said. KRI Nanggala-402 was built in Germany in 1977 and joined the ranks of the Indonesian navy in 1981. It was supposed to be decommissioned but because of limited funding, the government decided to upgrade it instead in South Korea, he said.

“It was an accident waiting to happen,” Ridzwan said."...

That's 44 years old...

https://gcaptain.com/how-old-was-missing-indonesian-submarine/

There can be a lot of speculation,... Maybe the sub hit a fresh water pocket, where it where it lost buoyancy. Or there was a release of methane from the methane hydrates on the ocean floor.

On a similar note, for the USS Thresher that sunk in the early sixties, (1961j there was speculation that there was a coverup, the navy’s official report was substandard welding on the piping.

and it was until recently that the reports were just release by court order, (due to a law suit by a retiring sub commander in 2019). That those reports were true.

It comes down to it can be a number of things... submarine environment is not for the faint hearted.

https://news.usni.org/2021/02/04/navy-releases-latest-round-of-uss-thresher-documents

I seem to recall something about icing in the strainers to the ballast tanks preventing the emergency ballast blow. This wasn't the root cause but the failure to be able to blow the tanks meant that the crew was not able to mitigate the original failure. P-9290 and Scope of Certification process was a direct result of the USS Thresher accident.

NAVSEA SS800-AG-MAN-010 P-9290 System Certification Procedures and Criteria Manual for Deep Submergence Systems US Navy

I understand, pointing to an item of the result why, but a cascading events from the root cause.

Since the incident, there were conspiracy theorist saying that there was a cover-up by the Navy. Until the lawsuit by the retired(ing) sub commander to release the documents of the incident by what the Navy.

As it turned out, this lawsuit actually showed there was no conspiracy, and what happened is what the Navy said happened, was actually true.

I just brought this up, as a possibility because I just recently came a crossed it.