Implosion Through Depth

[ChalkyWhite]

Can someone explain in detail just what Implosion Through Exceeding Crush Depth, actually means.
Recently I have seen a few TV programmes which have graphically illustrated, using computers,as to what happens to a submarine, or ship which exceeds it's 'crush depth'.

The Hunt for I-52, the loss of the USS Thresher,and the loss of the SS Derbyshire immediately spring to mind.

In the case of the I-52 it was eventually discovered 3 miles down in the Atlantic, relatively complete apart from the damage caused when it was sunk by depth charges and a couple of homing torpedoes dropped by aircraft.

The USS Thresher exceeded her crush depth as she had had to shut down her reactor and had therefore no power to either plane up, blow ballast, or otherwise extricate herself from such a critical situation which proved fatal. When the wreck was discovered it was apparently in a considerable number of pieces caused by implosion 8,400 feet below the surface.

The consensus it seems regarding the loss of the SS Derbyshire was that a small hatch right forward had not been secured properly allowing sea water into the forward hold. This created a domino effect as each successive hold was breached as the bow was forced further and further down through weight of sea water. All this took place in severe weather. When the ship eventually began to sink each hold successively imploded apparently and when the wreck was eventually found it was in pieces although still identifiable as the Derbyshire.

And what about Titanic. Why did this ship not implode at such a depth as it was found. What about Bismark too, found eventually at great depth. Neither of these ships had imploded.

I find this subject quite interesting and would very much like someone to explain these anomalies. Perhaps I'm missing something. Perhaps with a submarine, which exceeds crush depth, the pressure hull ruptures, but the exterior of the boat remains in one piece.Not so for the Thresher though. Why, in some cases, has a vessel been literally torn apart whilst in others it just sinks and remains whole.

I'm quite sure some of our knowledgeable members will be able to answer this question in the usual double quick time and I look forward to some replies.

Happy New Year One and All.

Chalky White.

[Harley]

I am no naval architect or much of a science student, but here's my rather amateur take on things.

As far as I see it, implosion occurs when the pressure on the outside is far greater than that on the inside - something which can't be common with sinking ships as they'd be full of water as well.

I-52 would have been depth charged and flooded in shallow waters. Presumably the pressure hull would have been flooded and consequently with the pressures equalised nothing would be crushed.

"Thresher" descending below her pressure depth would have been a case of catastrophic implosion. If I recall a documentary on "Thresher" it was supposed that she sank stern first into the deep - a rather horrible thought.

MV "Derbyshire" - it depends which view you take. The pressure could have crushed the hold covers, or as has recently been postulated a rogue wave smashed the ship.

"Titanic" had been rapidly flooding for hours before breaking in two and sinking, and would have filled rapidly on the way to the bottom.

"Bismarck" was essentially a burning hulk full of holes when she went down, and if her seacocks were wide open she'd be a giant collander. No problem with pressure there.

That's my amateur take on it all.

Simon

[John Odom]

Harley, Simon has it right. To implode (or explode for that matter) there must be a large pressure differential between inside and outside of the object. If a submarine's pressure hull is intact and it exceeds srush depth, it will implode. The calculated crush depth has a certain margin of safety built in, and several US subs exceeded nominal crush depth by a little bit, and survived in WWII. If the hull is not intact, the pressure will equalize before crushing can occur.

[ChalkyWhite]

Thanks for your replies chaps.

Chalky White

[FTM127]

This was a very interesting thread.

I can't add more to the technical details, however, the human side could be vastly different. With an implosion, human life would be extinguished in a matter of seconds or even miliseconds. With a gradual flooding, termination of life would be prolonged, particularly when air pockets existed. The courage to ship on a submarine just might be the bravest thing a seaman can do. Anyone who has the courage to serve in this branch is a very brave person. I think this was more so in WWI and WWII than today. Modern subs are much safer.

The Thresher was a mistake in welding. In an effort to cut costs, the manufacturer implemented a more 'efficient' welding procedure and eliminated certain quality control checks. The resulting catastrophe put an end to such slip-shod manufacturing. It always makes my blood boil to think that some bureaucrat got off scott free while good men died. I think there is an important lesson here for those that build war ships.

Fred

[ChalkyWhite]

Thank you for your answer Fred. This is a very interesting subject and I am not sure that I fully understand why some ships implode even with the detailed explanation given by Simon earlier. Obviously a ship sinks when water is taken aboard, for whatever reason, and the buoyancy is then affected in that the ship weighs more than the water it displaces. For example a warship, in action, would have all watertight doors closed thus preserving air space. Even a depth charged submarine would not be flooded in it's entirety but would have taken on enough weight of water to affect it's buoyancy thus sinking it.
Bismarck might have ben a battered wreck but there must have been countless compartments still containing air.

Regarding the USS Thresher this was a particularly nasty incident when brazed joints failed and caused flooding which in turn caused the reactor to shut down. As Simon mentioned it is thought that the ship sank stern first at increasing speed until crush depth. Some garbled voices were heard which ended it is thought with ...test depth. Unfortunately this was not recorded apparently as with modern equipment those garbled messages could now be properly analyzed. With regard to Fred's comments about responsibility this is what Admiral Hyman Rickover, the father of the nuclear submarine said at the inquiry into the loss of USS Thresher in 1963.

RESPONSIBILITY

Responsibility is a unique concept. It can only reside and inhere in a single individual. You may share it with others, but your portion is not diminished. You may delegate it, but it is still with you. You may disclaim it, but you cannot divest yourself of it. Even if you do not recognise it or admit it’s presence, you cannot escape it. If responsibility is rightfully yours, no evasion or ignorance, or passing the blame can shift the burden on someone else. Unless you can point your finger at the man who is responsible when something goes wrong, then you never had anyone really responsible.
Ends.

Fantastic words I recorded many years ago and never forgot. How many persons can you think of to whom such words apply?? I can think of a few politicians for a start!

I hope others will add comments to this thread and we can have a proper discussion electronically about this subject.

Chalky White

[FTM127]

Responsibility has many aspects. One of my mentors, Peter Drucker - the father of management as a science, traced management responsibility back more than 2,000 years to the Hypocratic Oath: Primum Non-Nocere, Above All Else, Do No Harm. Peter believed that when an individual becomes responsible for other's he assumes this mantle of responsibility. What we see with the welding changes to the Thresher AND the current world financial crisis is the effect when this responsibility is subjected to personal benefit and greed. We need to rebuild management values and responsibilities that have become so compromised by short term rewards and decision making.

Fred

[HMS Bergamot]

As a diver, I can tell you that the deeper you dive, the less buoyant you are. What is neutral buoyancy at 20 metres can quickly become negative buoyancy at 30m, or positive buoyancy at 10m.

The deeper a sub dives, the less buoyant it becomes due to compression of the hull, of the air in the tanks, or its fuel. A myriad of reasons, in fact.

I wrote recently about k-5, and how the air let into a buoyancy tank had first to reach the pressure of the water in that tank, and then exceed it before water could be forced out and buoyancy increased. That delay can prove to be fatal.

As has been said, there has to be an imbalance of pressures (less inside, greater outside) to cause implosion. I would posture that only basically water tight vessels can implode. Those that are freely flooding, generally don't.

[FTM127]

I think Chalky's point regarding "Responsibility" is of the utmost importance.

In the UK, you have the Monarchy and a thousand year old tradition of chivalry. There was a phrase we learned growing up: "No·blesse oblige" or nobility obligates. Those people who manage others also have obligations as to the welfare and treatment of those people. Today, leaders of government, business, the military and society have 'lost' that understanding of their obligations. This is the underlying cause of much of the failures in modern society. The balance needs to be restored.

Fred

[FTM127]

The point about the diver is interesting. I read somewhere that a whale, diving in the deep ocean, experiences extraordinary pressure on it's organs such that the lungs shrink something like 80 percent. They evolved the ability to handle such pressure over millions of years. Humans can't exist under such pressure. It's not just the absence of air. Some people can't dive more than ten feet without ear pain. I don't know what the limits of a dive would be? For example, with different breathing mixtures, people can even live in deep water for a short time, allthough this is no doubt limited to a few hundred feet. The human body is a marvelous mechanism: an engineering marvel really, but we are creatures of the surface by natural design. In the absence of pressure, space, different problems exist. Astronauts retuning to earth may experience muscle problems and bone loss. There is much to be done in developing environmental suits and habitats that enable us to work or exist for any length of time outside of our "comfort zone."

Fred

[culverin]

Another very valid point here is you will no doubt notice virtually every sub lost in action and when the wreck is discovered, is in fact in one piece, except for the area damaged, whether it be mine, depth charge, bomb, gunfire, collision, or any other means which has compromised the integrity of the pressure hull, from an external source, OR from an internal explosion ie Kursk.
All boat remains where the pressure hull collapsed or imploded will be found to have occured in accidents once that boat hits its crush depth.
Recent Western examples of the latter are Thresher, Dakar, Minerve where the victims remains, ie big debris field, have been discovered. The jury is still out on the Scorpion.

[steve roberts]

Probably the most horrible way to die,be it submarine or surface ship.It has been scientifically proved that implosion of a Pressure hull or compartment instantly starts a pressure wave fire incinerating everything in the compartment or submarine.I would have thought that any one still alive at that point would be killed or rendered incapable of thought,by the instant increase in pressure.Can you imagine the thoughts going through some ones minds in the minute or so that it takes to reach Crush Depth? The Scorpion is relatively intact forward,so that implies water within the hull before crush depth.The after ends have been telescoped up to the reactor compartment,which indicates still dry on reaching crush depth,therefore men alive in those compartments.In the Thresher's case,there would not have been much time to think about it as they were already at or near maximum test depth,when the "Incident" occurred.Though one factor in this loss was the boats inability to "Debalast" at this depth.In other words there was insufficient reserve buoyancy in her ballast tanks!.Most other sub wrecks found intact must have been fully flooded before hitting the ocean floor.
Regards Steve.

[culverin]

In fact moving back to #6, the loss of Thresher and Scorpion in the 1960's amply illustrates the implosion idea. All parts of the boat not subject to pressure, in other words virtually all of it external to the pressure hull, was discovered intact. As you would expect.

The discovery of the Israeli Dakar reinforced this, as a good portion of her fin was subsequently raised, almost intact.
There are still big questions in Israel as to the cause of her loss.
There is no mystery, and never was.

[steve simons]

sorry to pick up so late on this intersting thread, but one or two of the points raised I might have some information on. USS Thresher apparently had a reactor scram at depth, and kept trying to blow her main ballast tanks but because of the depth and the temperature of the water (ie very cold) the main ballast tank control valves froze open thereby draining the main bottle groups and emergency bof of holes in the huleottle groups and HP air supply so the compressors could not keep up, unfortunately leading to implosion once she had gone past her (DDSTP./ deep diving system test pressure). USS Scorpion I believe had a hot run of one of her loaded torpedoes; fired the affected tube only to find the torpedo came back and hit her (echoes of I think HMS Edinburgh although some sources say it could have been a russip to sinkan torpedo) hence the so called explosion. RMS Titanic obviously hit the iceberg causing holes in the hull apparently not as thought one long gash in the hull as previously thought but a series of holes in the hull which leaked into the hull as the forward bulkheads did not go to deckhead level but stopped short thereby leaving gaps where water could flood from one compartment to another.This would then made the bows heavier putting extra load on the forward part of the ship causing the ship to sink bow down but due to the apparent quality control of the rivets it may have caused the ship to break into pieces as different parts of the ship flooded at different times. While referring to the Bismarck there is once again some debate as was she sunk or scuttled? Either way both scenarios fit as HMS Dorsetshire torpedoed her both port and starboard which would equate with the sea cocks being open as the ship sunk on an even keel
sorry to be so long winded but that's just information I have read and picked up over a period of time