Seems like a pretty stupid design if you ask me

It’s pretty bad, but when the door accessible from the inside implodes from the insane pressure of the water around it, that’s even worse.

The door can still be designed to open outward and also able to be unlatched from the inside: those aren’t mutually exclusive properties.

It needs to remain perfectly watertight at over 5000psi or everyone dies. That design constraint probably eliminates most clever latch designs.

I was imagining a round door in the middle of the hull, like a submarine hatch, but it looks like the entire front dome comes off and that’s the “hatch”. If so, can’t they just make the front a giant screw and add handles to both sides?

The dome shape is a structural necessity to withstand the pressure, like in a soda can. Else you would need more material, more material means more weight, more weight means more bouyancy required which again means more weight etc.

It's like designing a spacecraft but with different constraints.

It's pretty much the exact opposite of designing a spacecraft.

Then let me amend what I wrote: It's as difficult as designing a spacecraft, because you reach the limits of what materials that can be used can offer.

Well, once you are in space the forces are pretty tame until you get hit by something. But the ocean never rests from trying to kill you, even the smallest material defect can cause an implosion. Personally I think designing for a delta of 400 atmospheres in compression is much, much harder than for 1 atmosphere in tension.

But it's withstanding pressure(called external pressure, yesterday I learned), so can't they just have a clean, stepped flange to mate and to prevent slipping off, plus a simple lock to prevent unintended disengagement?

This is usually done with a plug hatch and it's not that complex. The Alvin submersible has one and it's from 1964.

Exactly. There are so many lessons learned already when designing a device like this there is no point in re-learning them the hard way, just adopt a tried and true design.

That's what they did? Alvin is an outlier; other bathyscaphes used the (tried-and-true) bolt-in method.

Assuming they're out there near the surface bouncing around in 6' waves and whitecaps, what they need isn't a door they can open and drown themselves with. Seems like what they need is a more effective location broadcast.

We don't actually know that they don't have good ways of being found. If they do, it makes it all the more likely that the sub is on the bottom :-(

I think in that situation there is absolutely no good outcome and you’ll take whatever ends it as quickly and as painlessly as possible.

Doesn’t seem like a good trade off against bobbing around the surface and slowly dying sealed inside a capsule to me.

It's traditional in deep submersibles design, dating back to bathysphere. You probably weren't hanging around when they were designing them

Tradition itself is probably the worst rationale for an engineering solution. Maybe it's the right way for other reasons?

I didn't interpret "traditional" as the rationale, but rather just pointing out that they're always done that way — I assume/hope for good reasons other than tradition.

Traditions emerge from "other reasons". There is probably not enough excess buoyancy to open the hatch without flooding, so without external support you're dead anyway.

I could see that as being the simplest/least failure prone way to design a closing mechanism that doesn’t need to resist the immense pressure to maintain integrity, but rather is held more forcefully to the hull as the pressure increases. Certainly you could design something like that that bolts from the inside instead, but perhaps the problem with that is that they cant exactly carry along with them various tools and equipment they might need in the event that there is difficulty reopening it.

If you pass out, how do they get you out?

Two hatches? One opens from the inside one opens from the outside? I'm sure there are other solutions.

But as somebody else already pointed out: even if you get out in the middle of the ocean you're in real trouble, which makes the hatch issue kind of moot.

And that's twice the sealing surface to potentially fail.

It could be the same hatch. Very common on submarines.

You know what's the worst? Someone barging in into an established engineering domain and making spot judgements. This is simply incredible hubris.

If some brilliant improvement occurred to you in the first 5 seconds of hearing about some technical solution chances are this thought visited others in the past 100 years working on the problem for a living.

It sounds like they could use some improvements, 5 people are probably dead now. Out of how many trips in that submersible? I don’t know, just wondering, but it can’t be that many. Certainly not comparable to commercial airlines. So that’s a pretty high failure rate. Being able to open the vessel from the inside in an emergency probably wouldn’t have saved them, it’s just the first thing that is too much of a red flag for me to personally ever step foot in that thing.

I also don’t even understand why that vessel needs to be manned at all. With today’s high def cameras and displays, including VR, they could outfit an unmanned vessel with high def cameras everywhere, a fiber optic tether to the surface to carry the high def signal (or even wireless to some degree if they could make that work), and the operator could sit in a control station either on the boat at the surface or streamed over the internet from home, controlling the vessel however he wants, with high def screens to simulate the viewing experience of being in the vessel. I’ll bet it would get you 99% of the way there without having to risk your life. It’s not like anyone is getting out of the thing to swim around the titanic in scuba gear anyway.

There is no hint that its probable demise had anything to do with hatch design so far.

This is a recreational dive, there's absolutely no need for it as for most recreational activities.

There are quite a few other manned submersibles designed for extreme depth that do allow for the hatch to be opened from the inside, in fact that's most of them. Alvin's design would be a nice starting point. It can be opened both from the outside and from the inside.

As for what the probable cause is: we don't know, we may never know. But with a device that was apparently designed by another party who declared it unfit for purpose anything goes.

Do passengers also need to undergo decompression before exiting the craft?

No, the crew remains at 1 atm and the hull bears the pressure difference. Ocean pressure at the Titanic’s depth is over 400 atm (6000 psi!) but the oxygen level in normal air becomes toxic under higher pressures. The record is 70 atm for a couple hours by breathing 0.5% oxygen and 99.5% hydrogen (this is so extreme that it can’t even explode).

That's what Gus Grissom said.

Lot of people probably won't get the subtext on this one.

(although he was recently-probably-exonerated in that case).

I think it’s more the Apollo 1 door opening to the inside and secured by nonexplosive bolts, rather than the spuriously blown door on Liberty Bell 7.

FWIW, while NASA may had thrown him under the bus, his comrades in the astronaut corps believed him. Wally Schirra on Sigma 7, refused to blow the door until the capsule was on the Kearsarge. When he climbed out, he showed the bruise on his hand — the same bruise every one got when they pushed the escape button. The same bruise Grissom did not have.

https://www.npr.org/2021/07/22/1019254674/gus-grissom-libert...

That's the most horrifying detail of the whole affair, to me.

Could they just have some drills with diamond-tipped bits stored inside for emergency use? If needed, drill through the whole shell, stick an arm out and unbolt from the outside.

Or maybe a jackhammer to just hammer through whatever glass is there for observation purposes.

I don't think there is any glass. Both of the end caps are supposedly titanium and there are cameras.

At that point just watch a video, or drive an unmanned submersible.

I think the point is to reduce cost and speed up operations by not having a tether. You can't do wireless video under thousands of feet of salt water. The options are AI or humans. There is a podcast and a news video linked here on HN.

That's not true. There is a "large viewport", per their website:

https://oceangate.com/gallery/gallery-titan.html

before the inevitable: https://archive.is/ypr1t

> Or maybe a jackhammer to just hammer through whatever glass is there for observation purposes.

I'm now wondering if a jackhammer applies more force than the ocean at titanic depths. I suppose less uniform force at least.

why would a sub be carrying a jackhammer? that makes no sense

> Could they just have some drills with diamond-tipped bits stored inside for emergency use? If needed, drill through the whole shell, stick an arm out and unbolt from the outside.

A shaped charge might be a more sensible solution, but it's still within incredibly dangerous territory.

it should be findable by simple radio/celular contact?

This is under water. Radio/Cell do not penetrate beyond a few centimeters. Communicating underwater is usually done via acoustics.

but the op said "If the mother ship can not find the sub the occupants could be trapped bobbing just below the surface until their air runs out."

just beneath the surface

In submersible tech, just beneath the surface is 0-30m depth basically (for salt water). Cellphones signals are about 2m max while higher frequencies (eg 2.4GHz) drop off exponentially so are <1m

Antennea can trivially extend over 30m, and can float on the surface. As a wire attached to an inflatable float, for either bidirectional communication or as a GPS beacon, or both, the complete solution could exist for less than $10k and less than 10 kilograms to solve this. Why doesn't this exist for this craft that can only be openned from the outside?? There exists the ability to communicate from directly above, so why can't it also communicate (further) through open air while bobbing near the surface?

You seem to be under the impression that the people paying a quarter million dollars to get bolted shut in an experimental sub to go see the titanic are reasonable and people who would think of that. They aren't.

> usually

I'll just leave that there.

They have some type of radio link that works at depth for simple texts messages, but they have to be right above it.

That doesn't seem right, do you have any source? VLF wouldn't stand a chance of reaching that deep and ELF requires extremely large antenna to work. More likely they were using some form of underwater acoustic communication, sending and receiving data through sound instead of radio waves.

I don't have information about the type of communication link. I shouldn't have called it a radio link. Acoustic probably makes more sense. It was something very slow, so that sounds right.

According to David Pogue (journo who did a dive on this vessel last year), at least as of last year there was no beacon to transmit location. One would hope radio would be working, in that case.

Source: https://twitter.com/Pogue/status/1670826522138091521?s=20

>sealed from the outside >no location beacon

Wtf is anyone thinking getting in this thing?

The set of people that would enter an experimental sub to visit the titanic, and the ones that would do it with a craft that is bolted shut from the outside, is probably close to even.

Add to that the $250000 price tag qualifier

And literally steered with a cheap game controller. There's a YouTube video from CBS of their reporter taking a trip on this thing. It's almost comical how cheap it seems.

What’s wrong with game controllers? They are built to be ergonomic and in use for extended periods of time. Also a lot of people are already familiar with how to use them.

Not saying we should replace every bespoke interface with a game controller, but using a game controller isn’t necessarily bad either.

Good point. Might be nice to have some redundancy if a game controller is used for a mission critical component, but apparently, the US military approves.

https://www.theverge.com/2017/9/19/16333376/us-navy-military...

The key here to me is they use it for periscopes. An important function, to be sure, but no one is dying if the periscope controller fails. That isn't the same for the controller on the submarine where it controls lateral movement, which is critically important when going near a shipwreck or other hazards.

> What’s wrong with game controllers?

They are made for living rooms and not salt water marine environments.

>What’s wrong with game controllers?

I saw a video where he said they used the controllers' built-in bluetooth. Bluetooth is anything but mission-critical. Imagine a disconnect when you're trying to decelerate.

I wonder if it at least had a radar reflector. This area of the Atlantic is notorious for fog, on account of the current which brought the iceberg there mixing with the 'gulf stream' (more formally known as the North Atlantic Drift here.)