[PSUBS-MAILIST] Titan submersible missing at Titanic site

Mon Jun 19 21:05:26 EDT 2023

Composite pressure hulls are not unprecedented. I can think of the ISE Wrangler as an example, which was a GRP hull. The failure mode can be predicted with reasonable accuracy. Less so the failure stress. Composite hulls are considered in the rules (ABS), but require destructive testing of a series of identical hulls in order to characterize the failure pressure with acceptable statistical probability for acceptance by the classification society. As you mentioned, the failure modes are typically brittle, not ductile. True isotropic behaviour is also difficult to obtain in composites, and they are not particularly tolerant of damage.

Among the PSub community, I am not aware of anyone employing a composite pressure hull, though many use composites in non-pressure-boundary components, like fairings, and of course syntactic buoyancy foams. Use of fiber reinforced composites I wouldn't advise unless one was a professional engineer with the requisite specialist experience.

Sean

-------- Original Message --------
On Jun. 19, 2023, 18:08, Ian Juby via Personal_Submersibles wrote:

> So do any of you guys have a pressure hull of fiberglass or carbon fiber? I've been pondering this over in my head. The Titan's carbon fiber hull is, I believe, unique to deep submersibles. It also had this very sophisticated sensor system all over the hull, monitoring its health. The thing is, carbon fiber has no give - it simply catastrophically fails. This is the issue with using it on aircraft - it doesn't bend like metal does, it breaks. So what exactly does this hull sensor system look for or listen for? And if it detected problems? I don't think it would make any difference at all by that point - the hull would have failed long before the pilot had a chance to ascend to relieve pressure. I would think the time between the sensors detecting a problem and the hull catastrophically collapsing would be, at most, 10ths of a second. But I could be wrong - I just base that on my experience with the stuff.
> They were 1:45 into a 2-1/2 hour descent when contact was lost - so they hadn't even made it to the bottom yet - but still hitting over 9,000 feet. That's some pretty serious depth already. It's unlikely they made it to the Titanic and got entangled or trapped in the wreck somehow because it gets its navigation from the surface ship. So if communication is lost, they are also lost in terms of navigation. This is precisely what happened last year when that CBS reporter was aboard. The pilot on yesterday's dive would have scrubbed the dive if they had lost comms and thus navigation.
> Also let's bear in mind the loss of the Thresher - there was some kind of thermal plane at about 100 foot depth that kept both the Thresher and the Seawolf (the submarine trying to find the Thresher) from communicating with surface ships. Is it possible the Titan encountered some kind of thermal plane similar to that which disrupted their communications? But the fact that they still haven't had contact in a day and a half is telling me this is a recovery operation, not rescue. :(
>
> Just spitballing here - am I off the mark? Have any of you guys had a composite pressure hull?
> Ian
>
> On Mon, Jun 19, 2023 at 6:25 PM Douglas Suhr via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>> Thank you everyone for the info on this sub and her current situation. The fact that they are bolted into the pressure hull from the outside is a bit eerie, but it sounds like there's a lot of redundancy when it comes to surfacing. Hopefully the next 12 hours will bring good news. ~ Doug S.
>>
>> On Mon, Jun 19, 2023 at 6:12 PM irox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>
>>> I believe the hull is made of carbon fiber and the submersible wasn't certified any regulatory body (ABS/Lloyds/etc).
>>>
>>> This video gives some idea of the operation:
>>>
>>> https://www.youtube.com/watch?v=29co_Hksk6o
>>>
>>> They read the waiver terms and conditions at 2:40 mark. At the 7:27 mark they show a previous expedition where they lose communication with the sub and it gets "lost" (since it depends on topside of navigation data) for a couple of hours.
>>>
>>> Hoping for the best.
>>>
>>> Ian.
>>>
>>> -----Original Message-----
>>> From: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
>>> Sent: Jun 19, 2023 2:17 PM
>>> To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
>>> Subject: Re: [PSUBS-MAILIST] Titan submersible missing at Titanic site
>>>
>>> I'm sorry to hear this news. Hoping and praying the sub is found quickly with no loss of life! What do we know about the Oceangate Titan submersible? Hopefully at least 72-hrs of life support for its five occupants? ~ Doug S.
>>>
>>> On Mon, Jun 19, 2023 at 3:58 PM Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>
>>>> I agree.
>>>>
>>>> Jon
>>>>
>>>> On Monday, June 19, 2023 at 03:18:23 PM EDT, via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>>
>>>> https://www.bbc.com/news/world-us-canada-65953872
>>>>
>>>> Looks not good..
>>>>
>>>> Emile D.L. van Essen
>>>>
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