Titanic tourist sub missing

[Andy_Ross]

I think it's some kind of misunderstanding. DSRV has to equalize with sub it's rescuing people from. That might be above 1 atm, if they took some water .. but it also might be just original 1 atm. The pressure inside won't be much over 5 atmospheres, as nitrogen becomes toxic after that. Certainly at 1500 m depth, nobody would be alive inside if the sub was open to the sea.

DSRV would dive, dock, ideally communicate with the crew inside, increase pressure inside DSRV as needed, open hatches, transfer crew.
Decompression might still be an issue, but the hull of DSRV still has to stand to 150 atm of pressure.
Increasing pressure inside DSRV let's say to 5 atm would decrease the load on the hull .. but at 1500m it wouldn't make much difference. But it would indeed allow DSRV to work as diving bell in shallow depths, which still might be useful.

Nitrogen would be replaced by helium and oxygen reduced to anoxic levels the same as for any other saturation dive. But, as you say, I don't think that's how it operates.

 

[IsThisTheLife]

Details

LoL.

 

[Dr.Sid]

Nitrogen would be replaced by helium and oxygen reduced to anoxic levels the same as for any other saturation dive. But, as you say, I don't think that's how it operates.

Not for the survivors on the sunken sub.

 

[Andy_Ross]

Not for the survivors on the sunken sub.

But as you pointed out they would be at 1atm as would the crew of the DSRV. If it was rescuing from a sub it wouldn't be operating as an open bell.

 

[The Man]

The more I look into this, the more it appears that the problem of differential expansion and contraction between titanium end caps and a carbon fiber cylinder isn't actually solvable. You certainly wouldn't want to use a joint that slides or flexes. Even if you could come up with an expansion joint that can hold out the pressure, which I'm pretty sure you can't, you might as well forget the CF and Ti and make the whole craft out of that expansion-joint material.

Stronger adhesion (mechanical mixing and application in a clean room, vacuum treatment to remove bubbles, autoclaving to cure the adhesive, etc.) would probably have helped the submersible last longer but I can't see that alone preventing the differential expansion from crumbling the CF over time.

Oh, no doubt it had a very limited life cycle time even under the best construction methods currently available. However, you don’t have to start the cyclic clock already almost in the negative. Oh, we got to patch this up after X number of dives, let’s go to Z dives and see what that does. **** the sound warning system, alarms were blaring all around already.

Again why I think they might have been trying to push turn around time to get as much out of it before it just fell apart on deck. Like this..

 

[novaphile]

In 500 years time, online etymology dictionaries will have entries for "the job was rushed" saying "back in the 21st century a man named Stockton Rush made a submarine..."

Side by side with the current "rush job" will be a new term, known as a "Rush job".

And it will become synonymous with shoddy, botched, corner cutting, hubris.

The man deserves this legacy.

 

[PartSkeptic]

I've seen similar warnings for such things as fuel injectors, which won't cut your fingers off but will tattoo you in ways you may not have intended.

Again in a somewhat less drastic manner the stretching of bolts is also something one runs into sometimes in automotive applications. I used to do some work on Mercedes, and their head bolts were designed to be tightened to a specific torque and then exceeded, not by specified torque but by degrees of rotation. Bolts thus stretched were not supposed to be reused.

Yes. Not only Mercedes. I also saw this in various automotive workshop manuals.

 

[PartSkeptic]

Company testing
I used to do some research and development. Part of that included solving some issues relating to long term slow degradation of materials subjected to an oxidizing natural gas flame.

I set up a cylinder of various materials and coating and then ran them day and night for weeks. Aluminum failed. Stainless steels of various type failed. Ultimately I used a mild steel roll coated with a ceramic. Tested for weeks to be sure it did not delaminate. It worked well in service 27/7 365 days a year.

Other new designs were lab tested as well. Crude but effective tests. Inexpensive also when done in house.

Sub design tests
Computerized modelling is limited. Great for indicating modes of failure or where to look. But no substitute for lab testing.

Why did they not take a small section of carbon fiber and titanium glued together and subject it to cycles of heat and pressure then cut it open and examine it microscopically? Then test other sections for fail before and after cycling. They would at least get an idea of how the glue held up.

Did they do this to the first version that they scrapped? Cut and examine?

To my mind, these tests should be done by a lab to get information of how the sub could have failed.

Legal
If I was the lawyer for the families of the deceased I would be asking for the results of such tests and if none, ask why none. It would go to recklessness and neglect of duty of care.

It is my opinion that a waiver is not 100% exclusionary. The sub owners have to ensure that they are not knowingly negligent or reckless. I learned this before signing a medical waiver for an operation.

 

[PartSkeptic]

The more I look into this, the more it appears that the problem of differential expansion and contraction between titanium end caps and a carbon fiber cylinder isn't actually solvable. You certainly wouldn't want to use a joint that slides or flexes. Even if you could come up with an expansion joint that can hold out the pressure, which I'm pretty sure you can't, you might as well forget the CF and Ti and make the whole craft out of that expansion-joint material.

Stronger adhesion (mechanical mixing and application in a clean room, vacuum treatment to remove bubbles, autoclaving to cure the adhesive, etc.) would probably have helped the submersible last longer but I can't see that alone preventing the differential expansion from crumbling the CF over time.

Agreed on all points.

I have a patent for an aeroburner. Virtually every joint and part was designed to allow sliding to accommodate differential expansion. Only one point of any part was tightened to hold them together. The forces are too great to try and stop them.

 

[MRC_Hans]

I think it's some kind of misunderstanding. DSRV has to equalize with sub it's rescuing people from. That might be above 1 atm, if they took some water .. but it also might be just original 1 atm. The pressure inside won't be much over 5 atmospheres, as nitrogen becomes toxic after that. Certainly at 1500 m depth, nobody would be alive inside if the sub was open to the sea.

DSRV would dive, dock, ideally communicate with the crew inside, increase pressure inside DSRV as needed, open hatches, transfer crew.
Decompression might still be an issue, but the hull of DSRV still has to stand to 150 atm of pressure.
Increasing pressure inside DSRV let's say to 5 atm would decrease the load on the hull .. but at 1500m it wouldn't make much difference. But it would indeed allow DSRV to work as diving bell in shallow depths, which still might be useful.

Yes, that sounds realistic Still a different ballgame from "real" deep sea exploration, but that doesn't mean lessons can't be taken from this type of craft. At least this: You can bet these craft have their smsafety in order!

Hans

 

[Puppycow]

Well pipe with halfdomes is standard solution for shallower diving subs basically since day one. Typically with ring stiffeners, sure, but it is well understood geometry. That's not the issue.
The issue is combination of materials, together with likely sloppy manufacturing process, and certainly sloppy way of operating the vessel.

Key caveat highlighted.

 

[Samson]

Company testing
I used to do some research and development. Part of that included solving some issues relating to long term slow degradation of materials subjected to an oxidizing natural gas flame.

I set up a cylinder of various materials and coating and then ran them day and night for weeks. Aluminum failed. Stainless steels of various type failed. Ultimately I used a mild steel roll coated with a ceramic. Tested for weeks to be sure it did not delaminate. It worked well in service 27/7 365 days a year.

Other new designs were lab tested as well. Crude but effective tests. Inexpensive also when done in house.

Sub design tests
Computerized modelling is limited. Great for indicating modes of failure or where to look. But no substitute for lab testing.

Why did they not take a small section of carbon fiber and titanium glued together and subject it to cycles of heat and pressure then cut it open and examine it microscopically? Then test other sections for fail before and after cycling. They would at least get an idea of how the glue held up.

Did they do this to the first version that they scrapped? Cut and examine?

To my mind, these tests should be done by a lab to get information of how the sub could have failed.

Legal
If I was the lawyer for the families of the deceased I would be asking for the results of such tests and if none, ask why none. It would go to recklessness and neglect of duty of care.

It is my opinion that a waiver is not 100% exclusionary. The sub owners have to ensure that they are not knowingly negligent or reckless. I learned this before signing a medical waiver for an operation.

Are lawyers for the families indicated here?
In a bright future everyone would consider this a natural disaster, the undead would grieve for a nanosecond and split perfectly evenly the various fortunes.

 

[jeremyp]

As far as I can see from the description in your link it works on the diving-bell principle. If so, that is an entirely different matter. In a diving bell, you have the same pressure inside as outside, so you can have an open water surface. This is useful for rescue purposes, as these crafts seem to be designed for.

1500 meters is rather deep for a diving bell, though. There will be some VERY interesting compression/decompression challenges.

Hans

Hans

Unlikely if it goes down to 1,500 metres. Oxygen becomes toxic to the human body well before 150 atmospheres (I think it's about 100).

Then there's the practical problem of attaching your DSRV at whatever the local water pressure is to a stricken submarine whose internal pressure is one atmosphere. You have to equalise the pressure on both vessels in order to open any door between them. The pressure difference between the diving chamber and the outside world in the Byford Dolphin disaster was only 8 atmospheres - 9 inside 1 outside (equivalent to a depth of 90 metres).

 

[MRC_Hans]

Unlikely if it goes down to 1,500 metres. Oxygen becomes toxic to the human body well before 150 atmospheres (I think it's about 100).

Then there's the practical problem of attaching your DSRV at whatever the local water pressure is to a stricken submarine whose internal pressure is one atmosphere. You have to equalise the pressure on both vessels in order to open any door between them. The pressure difference between the diving chamber and the outside world in the Byford Dolphin disaster was only 8 atmospheres - 9 inside 1 outside (equivalent to a depth of 90 metres).

Yes I agree that these problems exist. However, since DSRVs are built for and used by several navies, there must be at least plausible solutions to such problems, although maybe all situations have not been tried.

Hans

 

[jeremyp]

Yes I agree that these problems exist. However, since DSRVs are built for and used by several navies, there must be at least plausible solutions to such problems, although maybe all situations have not been tried.

Hans

Yes there are, but it's highly implausible that the diving bell principle is one of them. That's my point.

 

[Ziggurat]

So here's a nice video about how to build a deep sea submersible in an actually safe way:

Basically it's a case study on how Alvin, a deep sea submersible that's been operating for several decades now, how designed and constructed. It's not a comprehensive breakdown of everything about the design, but it does give a decent overview and a sense of the scale of what's involved. And it contrasts quite sharply with Seagate and Titan.

 

[MRC_Hans]

Yes there are, but it's highly implausible that the diving bell principle is one of them. That's my point.

Well, I only refer to what it says in the description previously posted: : https://alchetron.com/Deep-submergence-rescue-vehicle

Hans

 

[MRC_Hans]

So here's a nice video about how to build a deep sea submersible in an actually safe way:

Basically it's a case study on how Alvin, a deep sea submersible that's been operating for several decades now, how designed and constructed. It's not a comprehensive breakdown of everything about the design, but it does give a decent overview and a sense of the scale of what's involved. And it contrasts quite sharply with Seagate and Titan.

Indeed!

Hans

 

[Andy_Ross]

As far as I can make out, they didn't even use any kind of checklist before or during a dive.

 

[The Man]

Company testing
I used to do some research and development. Part of that included solving some issues relating to long term slow degradation of materials subjected to an oxidizing natural gas flame.

I set up a cylinder of various materials and coating and then ran them day and night for weeks. Aluminum failed. Stainless steels of various type failed. Ultimately I used a mild steel roll coated with a ceramic. Tested for weeks to be sure it did not delaminate. It worked well in service 27/7 365 days a year.

Other new designs were lab tested as well. Crude but effective tests. Inexpensive also when done in house.

Sub design tests
Computerized modelling is limited. Great for indicating modes of failure or where to look. But no substitute for lab testing.

Why did they not take a small section of carbon fiber and titanium glued together and subject it to cycles of heat and pressure then cut it open and examine it microscopically? Then test other sections for fail before and after cycling. They would at least get an idea of how the glue held up.

Did they do this to the first version that they scrapped? Cut and examine?

To my mind, these tests should be done by a lab to get information of how the sub could have failed.

Legal
If I was the lawyer for the families of the deceased I would be asking for the results of such tests and if none, ask why none. It would go to recklessness and neglect of duty of care.

It is my opinion that a waiver is not 100% exclusionary. The sub owners have to ensure that they are not knowingly negligent or reckless. I learned this before signing a medical waiver for an operation.

In my engineering lab days testing for long term reliability was all it was about. You can always come up with some kind of test to accelerate cyclic exposure and see how things might hold up in their long term usages.