Comment by ceejayoz | Hacker News Reader

Comment by ceejayoz | Hacker News Reader

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I don't think you're missing anything. Others, including those in-the-know, were left scratching their heads too.

https://www.nytimes.com/2023/06/20/us/oceangate-titanic-miss...

> Years before OceanGate’s submersible craft went missing in the Atlantic Ocean with five people onboard, the company faced several warnings as it prepared for its hallmark mission of taking wealthy passengers to tour the Titanic’s wreckage.

> OceanGate’s director of marine operations, David Lochridge, started working on a report around that time, according to court documents, ultimately producing a scathing document in which he said the craft needed more testing and stressed “the potential dangers to passengers of the Titan as the submersible reached extreme depths.”

> Two months later, OceanGate faced similarly dire calls from more than three dozen people — industry leaders, deep-sea explorers and oceanographers — who warned in a letter to its chief executive, Stockton Rush, that the company’s “experimental” approach and its decision to forgo a traditional assessment could lead to potentially “catastrophic” problems with the Titanic mission.

My question is just... why?

It's not like carbon fiber was any cheaper than just making the thing out of steel or titanium like literally every other submersible. It just doesn't make any sense. You have none of the weight penalties that exist in aviation, so the heavier and the thicker the better.

As I understood it, you do have a weight penalty for a sub. You need to get back up by powered movement, or down by it. You are limiting your dive time either way.

They can’t use foam for flotation at that depth. There is a concrete like “synthetic foam” if you want unpowered rise to surface but it’s expensive. I read early on they wanted carbon to be light enough to get back up by releasing weights on powerloss.

From what I have seen of the hull, it was a tube. I can’t remeber seeing a view with a complex or even drafted shape to it.

I suspect that spinning carbon by fiber would take far too long, and think they probably used narrow weave to do it. It would have been cheaper than the required thickness of titanium, which is the same strength as steel, but 40% the weight and still a little heavier than aluminum.

Who knows!? Nothing they did showed that they ever chose the more expensive option. Carbon was likely just the cheapest thing they could use for their goals.

Especially if you buy your material because it is past shelf lofe, don't use an autoclav and forgoe curing.

Fun experiment: Take a roll from some toilet paper, squeeze it somewhat evenly at the ends. It is kond of stable. Then peel the layers apart, ans squeeze again. The same would happen if the composite tube delaminated at one of the end cap rings. This whole thing is beyond infuriating.

> don't use an autoclav and forgoe curing.

I haven’t read that. But, that’s not an option. Carbon won’t just cure on its own, ever. It will be a shitty sticky mess forever. It had to be cured somehow.

As to the carbon expiration. I don’t know what that was. I suspect it could be epoxy like in prepreg, but I doubt prepreg here. And it could be shelf life of the carbon itself as it can be hydrophilic in some cases.

From what I fpund, which admittedly wasn' a lot, the used pre-preg for the spining of the hull. Judgeing from the video, the environment wasn't too clean neither. Then they put all 480 layers for some hours into an oven at 160 (?) degree celsius. Thats it... Not testing afterwards, no aditional curing, no temp control during winding of the pre-preg (that is tricky enough already under ideal circumstances, 480 layers, the resin will be basically hardened, well dried, before the last layer is applied).

Allegedly, they bought expired (out of freezer time) prepreg from Boeing Surplus. Boeing has released a statement that they have no records of this, so it likely passed through a third party before he acquired it.

> Nothing they did showed that they ever chose the more expensive option.

It's so absurd. Deep sea tourism is going to be something only for the .1% for a while.

They can afford a vessel that's 1000x more expensive. Your market is about 50 people. They've got unlimited money, basically.

Why cheap out and die? I just don't get it.

I suspect their end goal was to sell deep sea subs to the oil and gas industry, and this was a testbed.

Why would you do that manned instead of using remote control?

I'm assuming your engineering requirements for an unmanned sub would be substantially easier for a number of reasons (not needing to worry about killing someone, mainly).

Can't fund it with rich customers who want to see the Titanic with unmanned subs.

> They can’t use foam for flotation at that depth. There is a concrete like “synthetic foam” if you want unpowered rise to surface but it’s expensive. I read early on they wanted carbon to be light enough to get back up by releasing weights on powerloss.

This would make sense. The first bathyscapes (FNRS-2, Trieste) used the same iron ballast method via electromagnets, but bouyancy was provided by an external tank filled with a liquid of lower density than water -- gasoline.

I hadn't heard of the foam before, but I looked to see how modern deep submersibles provided bouyancy. The first one I checked was the one I'm most familiar with from my childhood fascination with the Titanic -- DSV Alvin, commissioned in 1964 and taken by Robert Ballard on the very first expedition to the wreck -- and it uses such a foam developed around the same time. A minor correction, though: the foam is called "syntactic foam"; the term shares its etymology with "syntax": from Greek σύν (sún, “together”) and τάξις (táxis, “arrangement”). These foams are composite materials containing what they call "cenospheres" or "microballoons": tiny, rigid, hollow spheres. Why use a large steel ballast filled with flammable hydrocarbons when you can use thousands of much smaller ones made out of an assortment of materials from ceramic to titanium to polymers?

>>there is a concrete like “synthetic foam”

The word you are looking for is "syntactic foam", which is an epoxy or other material typically with embedded hollow glass microspheres. This material is used for the buoyancy components of undersea vessels. It comes in a broad variety of densities and depth ratings. It is typically machined into shapes on the inside of the part fitting around the metallic components and on the outside the shape of the outer surface of the vessel. It is also somewhat expensive, more for higher depth ratings (on the scale of dozens to low thousands of dollars per cubic foot). Here's a product from one of the suppliers I worked with for more info [0]

Typically, the goal in designing the vessel is to account for the mass and buoyancy of the metal parts and design in the right final volume of syntactic foam so that the vessel is neutrally buoyant at the operating depths, and doesn't have to work to stay up or stay down.

For more moderate depths, there are also various structural foams, which use a variety of chemistries to achieve low densities and high compression strengths. These are also used in sandwich panel construction for composites (instead of honeycomb, and for the same effect), e.g., [1].

Source: I own & run a composites design & manufacturing shop which does work on, among other things aerospace and undersea projects.

[0] https://www.trelleborg.com/en/applied-technologies/products-...

[1] https://www.gurit.com/structural-core-materials/

I knew that, but either bonehead, fatfinger, or was autocorrected. Good links tho.

> It’s not like carbon fiber was any cheaper than just making the thing out of steel or titanium like literally every other submersible.

Well, they were kind of proud [0] of buying carbon fiber from Boeing with a steep discount due to it being too old for aviation use, so maybe it was cheaper than steel or titanium, even if carbon fiber in general would not be.

[0] long before the accident; I doubt anyone at OceanGate would brag about that now.

I was more referring to TFA which seemed to assert that you can test carbon fibre, with some kind of EM radiation.

That it was all a mess at OceanGate, that bit I got :)

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