[PSUBS-MAILIST] Fwd: K-250 side viewport and dome hatch.

Tue Sep 29 07:03:42 EDT 2020

-----Original Message-----
From: vbra676539 at aol.com
To: personal_submersibles at psubs.org <personal_submersibles at psubs.org>
Sent: Mon, Sep 28, 2020 4:07 pm
Subject: Re: [PSUBS-MAILIST] K-250 side viewport and dome hatch.

The Nekton viewports were extensively tested in-house and cleared by ABS for service in the last 3 subs, Beta, Gamma, and Delta. The design came about as it was something they could build in a small shop, meaning the reinforcement rings (1" X 1" in cross section) could be welded in place, then machined flat with a purpose built (and portable) milling machine that fit right to each frame.
Drilling acrylic is problematic. The drill bits have to be modified with extra relief, and the temperatures are critical. And, of course, Marfab built all this themselves, and annealed the ports in-house. And for practical info, neoprene or rubber will not work as a gasket. Instead, a cork/neoprene blend is glued directly to the viewport frame (but not to the window). People poo-poo them these days, but added together the 4 Nekton boats made over 12,000 dives, over half of them done by Delta. Hard to argue with the kind of success rate.
As to the port broken in Beta, the problem was not the port itself, but its side exposure which left the acrylic unprotected from a side impact. As a comparison, Ashera broke a port in Greece and those were truncated cones as per modern spec. Happily in that accident, the two chunks of acrylic stayed together in the frame, and actually sort of self sealed. Leaky is better than busted, for sure. So just keep in mind the lessons learned: No heavy lifting overhead, dumbass (for Beta), and watch where you're going, stupid (for Ashera).
Vance

-----Original Message-----
From: Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Mon, Sep 28, 2020 12:26 pm
Subject: Re: [PSUBS-MAILIST] K-250 side viewport and dome hatch.

 Attachment holes through viewports are not currently accepted as safe practice even though there are some early model submarines that did utilize that configuration.  Sean could likely give a better description but in laymen terms those holes introduce stress and fatigue that could lead to development of cracks within the acrylic material and seriously weaken it.  I think the Nekton series used such a configuration but those submarines were certified and therefore went through intense engineering study and testing.  Any comment Vance?
Peter Madsen drilled holes in his view ports to attach them to his submarine UC3, but Peter was also a risk-taker generally and I don't believe he ever dove UC3 to any serious depth.  There's a video somewhere of him swapping out a view port underwater.

    On Monday, September 28, 2020, 10:57:13 AM EDT, Philippe Robert via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Upgrade on adding view port too. But now I will follow Jon advice,  better to do what I see on the plan.
Le lun. 28 sept. 2020 10 h 47 a.m., Philippe Robert <phelop at gmail.com> a écrit :

Ok.
Le lun. 28 sept. 2020 10 h 38 a.m., Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> a écrit :

"Upgrade" is a problematic term. When I design seals, I typically do an exhaustive evaluation to determine whether standard O-rings will work, and if not, then I start looking at other options. For this application, O-rings work well, and I am hard pressed to come up with any possible justification to use something different.

Sean

-------- Original Message --------
On Sep. 28, 2020, 08:17, Philippe Robert via Personal_Submersibles < personal_submersibles at psubs.org> wrote:

Thanks for the advice, my goal is to build my submarine safeste as possible, but if I can upgrade sealing and design it will be great.
Le dim. 27 sept. 2020 10 h 46 p.m., Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> a écrit :

In fact, there's nothing inherently wrong with rectangular cross section seals, provided they are implemented in the same manner as O-ring seals with a captive groove, managed extrusion gap, designed gap fill and designed maximum squeeze of the seal. Absent those controls, a simple flat gasket presents not only a severe risk of extrusion, but can be subject to damage and consequent failure if maximum squeeze is not constrained. When properly designed, however, rectangular cross section seals can perform essentially as an O-ring seal with integral backup rings in terms of extrusion resistance.

Standard O-ring seals have the advantage of having a massive body of performance data available, and a freely available comprehensive design resource in the Parker O-ring Guide (ORD5700). Seals with custom geometries will generally require independent design verification in the form of FE models and destructive testing.

Sean

-------- Original Message --------
On Sep. 27, 2020, 18:10, hank pronk via Personal_Submersibles < personal_submersibles at psubs.org> wrote:
Hi Philipe,
You have to machine the dome seat flat anyways, so adding an o-ring groove is a small extra step.
Hank 

On Sunday, September 27, 2020, 4:36:22 PM MDT, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote: 

Hi Philipe,
I don't know of any submersibles that don't use o-rings as the hatch sealing method.
I believe there is a danger of a flat rubber seal extruding inward under pressure.
Alan 

On 28/09/2020, at 10:32 AM, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Follow the plans.  The sections you reference are all related to the pressure hull and should not be modified.

Jon

On Sunday, September 27, 2020, 04:47:54 PM EDT, Philippe Robert via Personal_Submersibles <personal_submersibles at psubs.org> wrote: 

Hi all,

I currently make the conning tower. I see on the internet some k-250 with front and side viewport in addition of the acrylics dome. Some of the viewport is close to the gusset and I assume that is not possible to do a 100% weld. Is it acceptable ? Is it ok to drill hole in the viewport to put retaining bolts ?  Second question, on the blueprint, the sealing option for the hatch on the conning tower is o'ring groove. Is it possible to make better sealing like flat rubber strip or something like that ?

Best regards,

Philippe
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