Titanic tourist sub missing

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Smpl Mnmlst
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#3094298 24-Jun-2023 10:23

Rikkitic:

Doesn't invalidate my point. The sub could have been structurally weakened over time from bopping into other objects. 400 times more pressure just means the weak point would not have to be all that much weaker for collapse to occur.

I believe Titan has done something like 29 previous dives. Given its primarily carbon fibre construction, which is very inflexible and prone to shattering when it fails (as seen in the pressure video above), it’s easy to think that 29 cycles from surface pressure to ultra pressure and back, might generate undetected hairline faults that could grow each time - until ……

It’s probably been mentioned earlier in this thread but newspapers report that at Titanic depth the pressure is about 2,500 kg per sq inch.

A US expert commentator I heard on the radio also said that, given the hull tube was carbon fibre and two end pressure caps/domes were titanium, there could have a a failure due to differing flex characteristics of the two materials at their junctions when under ultra pressure.

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#3094300 24-Jun-2023 10:33

eracode:

Rikkitic:

Doesn't invalidate my point. The sub could have been structurally weakened over time from bopping into other objects. 400 times more pressure just means the weak point would not have to be all that much weaker for collapse to occur.

I believe Titan has done something like 29 previous dives. Given its primarily carbon fibre construction, which is very inflexible and prone to shattering when it fails (as seen in the pressure video above), it’s easy to think that 29 cycles from surface pressure to ultra pressure and back, might generate undetected hairline faults that could grow each time - until ……

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#3094304 24-Jun-2023 10:51

29 successful trips isn't insignificant.

eracode

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#3094305 24-Jun-2023 10:57

networkn:

29 successful trips isn't insignificant.

Not sure in which way you mean that but my point is that’s 29 trips where the vessel could have been deteriorating undetected.

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#3094312 24-Jun-2023 11:07

Apparently the original carbon fibre section on the Titan from 2017 was redesigned/replaced in 2020. This was only the 3rd trip to the Titanic since the rebuild. The company has other submersibles capable of lesser depths. Is 29 dives including all of them?

Edit There have been dives to other wrecks but I haven't found a list of the depths involved.

2nd Edit. Wrong information is all over the place. I think I'll wait for the reporters to stop making it up. The Oceangate site is either overloaded or gone on holiday.

eracode

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#3094313 24-Jun-2023 11:12

Bung: Apparently the original carbon fibre section on the Titan from 2017 was redesigned/replaced in 2020. This was only the 3rd trip to the Titanic since the rebuild. The company has other submersibles capable of lesser depths. Is 29 dives including all of them?

Sorry don’t know - you’re better informed on this.

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#3094314 24-Jun-2023 11:12

johno1234:

"Stockton Rush, the boss of OceanGate, previously admitted to "breaking rules" in order to build his company's Titan submersible, newly released footage has shown..."

https://www.newsweek.com/video-shows-titanic-sub-ceo-saying-he-broken-some-rules-make-this-1808039

Were these actual rules he broke, or conventional wisdom "rules". I imagine he wouldn't admit to breaking actual rules. Conventional wisdom "rules" (like a deep sea submersible must be a titanium sphere) are broken by entrepreneurs who believe that they know better. Sometimes they're right (as in the Wright brothers, where conventional wisdom was that powered heavier than air aircraft weren't possible) and sometimes they're wrong. If the Wright 1903 Flyer had unexplainably disintegrated and killed Orville, there would have been plenty of I-told-you-so critics.

Perhaps the difference between the Wrights and OceanGate was that the Wrights had proven every aspect of their aircraft before it flew... they flew similar gliders, under control. They created the world's first wind tunnel to measure airfoils. They calculated the required horsepower to fly, and got an engine built that met their requirements. The analysed propellor design. They used proven technology (bicycle chains) to transmit power from the engine to the propellors. They collaborated with other aircraft pioneers like Chanute.

By contrast, OceanGate didn't test the strength of their carbon fibre (arguably the most important aspect of the whole thing) "because it wasn't possible to test it". I imagine the Wrights, if they were building a deep sea submersible out of carbon fibre, would have built a suitable carbon fibre testing rig of some kind. If there was a potential fatigue problem from multiple dives, perhaps they would have build smaller mockups and dived them for 20 dives before the real one did its first. Then every actual dive, take a few mockups with you, and, if necessary destructively, test one of the mockups so that you're always seeing at least 20 dives ahead of the actual sub. This is engineering instead of wishful thinking.

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Canuckabroad

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#3094317 24-Jun-2023 11:35

I hear most of the discussion here being about the carbon fibre. If we're trying to armchair detective this, wasn't there a statement that their porthole for visibility wasn't certified for the depth used here? When you're trying to evaluate the strength of a system, I wouldn't initially assume part of the cylindrical body made of the same material was the weak point, but rather where that body transitioned to a different material which needed to be bolted in place from the outside.

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#3094335 24-Jun-2023 12:02

eracode:

Rikkitic:

Doesn't invalidate my point. The sub could have been structurally weakened over time from bopping into other objects. 400 times more pressure just means the weak point would not have to be all that much weaker for collapse to occur.

I believe Titan has done something like 29 previous dives. Given its primarily carbon fibre construction, which is very inflexible and prone to shattering when it fails (as seen in the pressure video above), it’s easy to think that 29 cycles from surface pressure to ultra pressure and back, might generate undetected hairline faults that could grow each time - until ……

It’s probably been mentioned earlier in this thread but newspapers report that at Titanic depth the pressure is about 2,500 kg per sq inch.

A US expert commentator I heard on the radio also said that, given the hull tube was carbon fibre and two end pressure caps/domes were titanium, there could have a a failure due to differing flex characteristics of the two materials at their junctions when under ultra pressure.

So, any bopping into other objects would have to have been above 2500kg/sq in to break the hull itself. For comparison, a hammer blow is about 67kg/sq in (600N over a 1 sq inch hammer head). If you were to hammer a nail with a 1 sq mm point on the hull, you're about 50,000 kg/sq in, so somewhere in between those would be required. But the hull was designed for uniform pressure from the outside... pressure on one side (e.g. a collision with the side of the ship) could have caused damage.

When a structure deforms, the load moves to the part that doesn't deform. In particular, any sharp corners concentrate the force (as they discovered with the de Havilland Comet aircraft). So, if (say) the titanium started deforming at 2,000 kg/sq in, the load on the titanium would start shifting to the carbon fibre... the carbon fibre would be holding the titanium in place. The part of the carbon fibre supporting the titanium might then be taking 3,000 kg/sq in. This kind of thing can be modelled using finite element modeling in CAD software. But of course it would be based on assumptions about how strong the carbon fibre was, which no-one really knew.

The Comet was also the foundation of much of our knowledge about fatigue, in this case the effect of pressurisation/depressurisation cycles of the aircraft on the aluminium skin. As you say, minute hairline cracks form at high stress points, which then moves the stress to the end of the crack (being a really sharp corner). So the next cycle the crack extends a little more, until eventually the structure fails. Interestingly, the way they replicated this was pressurising the Comet in water.

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#3094338 24-Jun-2023 12:07

Canuckabroad:

If we're trying to armchair detective this, wasn't there a statement that their porthole for visibility wasn't certified for the depth used here?

The viewport was only certified to 1300m. However, that doesn't mean it wasn't tested by OceanGate. I guess you would normally allow a safety margin of 50%, so you'd expect it was tested to 4,500m

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#3094340 24-Jun-2023 12:14

frankv:

So, any bopping into other objects would have to have been above 2500kg/sq in to break the hull itself. For comparison, a hammer blow is about 67kg/sq in (600N over a 1 sq inch hammer head). If you were to hammer a nail with a 1 sq mm point on the hull, you're about 50,000 kg/sq in, so somewhere in between those would be required. But the hull was designed for uniform pressure from the outside... pressure on one side (e.g. a collision with the side of the ship) could have caused damage.

IANA engineer, but I would have thought that an impact or collision (say with the side of the ship) at surface pressure could easily be inconsequential - but an impact when at ultra pressure, when the hull is already under max stress, would be something very different.

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#3094342 24-Jun-2023 12:16

frankv: Conventional wisdom "rules" (like a deep sea submersible must be a titanium sphere) are broken by entrepreneurs who believe that they know better. Sometimes they're right (as in the Wright brothers, where conventional wisdom was that powered heavier than air aircraft weren't possible) and sometimes they're wrong. If the Wright 1903 Flyer had unexplainably disintegrated and killed Orville, there would have been plenty of I-told-you-so critics.

Perhaps the difference between the Wrights and OceanGate was that the Wrights had proven every aspect of their aircraft before it flew... they flew similar gliders, under control. They created the world's first wind tunnel to measure airfoils. They calculated the required horsepower to fly, and got an engine built that met their requirements. The analysed propellor design. They used proven technology (bicycle chains) to transmit power from the engine to the propellors. They collaborated with other aircraft pioneers like Chanute.

By contrast, OceanGate didn't test the strength of their carbon fibre (arguably the most important aspect of the whole thing) "because it wasn't possible to test it". I imagine the Wrights, if they were building a deep sea submersible out of carbon fibre, would have built a suitable carbon fibre testing rig of some kind. If there was a potential fatigue problem from multiple dives, perhaps they would have build smaller mockups and dived them for 20 dives before the real one did its first. Then every actual dive, take a few mockups with you, and, if necessary destructively, test one of the mockups so that you're always seeing at least 20 dives ahead of the actual sub. This is engineering instead of wishful thinking.

at what point is it ok to carry paying passengers who knowingly sign their life away in experimental designs

i guess there are ethical, commercial and soon to be discovered legal aspect of this

Canuckabroad

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#3094343 24-Jun-2023 12:19

I watched a Youtube video last night which suggested that a 0.5% out of round condition decreases the structural strength by up to 35% because all the stresses aren't being equally shared any longer. If true then it wouldn't take a massive hit to have a big impact at depth.

Rikkitic

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#3094353 24-Jun-2023 13:05

I am also not an engineer, not even a little bit, but logic and the Mythbusters example I cited suggest to me that any deformation of the shell, even a microscopic one, might be enough to start a chain reaction that over time would eventually lead to hull failure as tiny additional deformations gradually accumulate. It's a bit like the Big Bang. There would be no galaxies or stars if the Creation snot had been perfectly symmetrical. It was the slight imbalances that enabled matter to ultimately coalesce (I think).

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eracode

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#3094377 24-Jun-2023 14:34

Batman:

eracode:

I believe Titan has done something like 29 previous dives. Given its primarily carbon fibre construction, which is very inflexible and prone to shattering when it fails (as seen in the pressure video above), it’s easy to think that 29 cycles from surface pressure to ultra pressure and back, might generate undetected hairline faults that could grow each time - until ……

When I talked earlier about pressurisation cycles and progressive deterioration, I hadn’t seen the James Cameron video that you posted. Interesting that he talks in exactly the same terms. Great clip.

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