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Very well thought out Ian. Thank you very much for your input, you make several very good points. James has been gone for a couple days, and should be back shortly to comment as well. That kind of response is exactly why James and my self wanted peer review. We had though there was perhaps a couple of novel concepts in that model. I've wanted a hatch configuration from the start, with K-250 type latches or the like. This would be for many reasons. Many of which you stated, like the extra thru hull issues. That model and drawings was just part of working thru ideas. The idea for James likely stemmed from the Nemo's front removable 135 degree dome arrangement, and so James was thinking in the beginning he would just copy that. The dome as drawn at that time, didn't have the outer edge squared up. Since I didn't know at that time, that is was going to be machined that way, and that it was a much safer way to go. The outer soft neoprene gasket between the retaining ring and dome is not ment to seal anything. It's just a soft seating surface to keep the metal away from the acrylic to deal with expansion and contraction issues, as well as not scratch the acrylic, much like my front lower flat viewport is retained on my K-250 with a soft pour rubber gasket and Dan H's hatch acrylic viewport. The R300 has a soft neoprene gasket between the domes flange and it's retaining ring as well. I had also the same thoughts as to the retaining ring, as it is in those drawings, as perhaps being hard and expensive to fabricate. Perhaps one like is on the S101's large front dome, which looks like a large rolled piece of flat SS stock, that is also formed to be conical and then a large number of bolt holes would do the trick. I don't know exactly how that one was produced. So I started my design with a lathe turned design. I don't really like the way the K-250 domes are attached to the seating ring visually as well as hydro dynamically. I do how ever like the way the R300 retains the dome with a bolted on flange that holds down the domes bonded on flange. This might be the easiest way to go if James decided to add on a flange like is done on the K-250's and the R300. I didn't know about hard neoprene gaskets being a good option when I was building that model. I would now replace that bottom O-ring with a hard neoprene gasket like is done on the R300's hatch, so one can easily remove and/or replace the dome with out a horrific ordeal. The inner O-ring on the lip was to be more of a none extruding spacer to keep the dome centered and away from the metal lip, as well as to resist the dome from coming inward so it couldn't poop out of the outer retaining ring, if there was a lot of internal pressure built up for what ever reason. One reason would be when the sub was quickly flooded, in preparation for a wet exit. I wouldn't want that dome coming out before I was ready to open or remove it. I made the retaining ring to be curved to the shape of the dome and to be higher then the one James showed us for better resistance to letting the dome poop out of it. I will need to do some FEA work testing both internal pressure being applied to the dome and external hydrostatic pressure to see how every thing holds up when in that configuration. Perhaps the inner lip O-ring should be larger and softer so as to put less concentrated stresses on the dome. That removable dome as configured in the drawings you saw, was not meant to be opened until the sub was already flooded in preparation for a wet exi(t, and the occupant(s) would likely be using SCUBA gear at that point. Your resident pipe dreamer ;)' Regards, Szybowski > Date: Sun, 31 Aug 2008 12:28:03 -0400 > From: irox@ix.netcom.com > To: personal_submersibles@psubs.org > Subject: Re: [PSUBS-MAILIST] Wet Exit Removable Front Dome CAD Models > > Hi Brent, > > a CAD drawing is worth a 100 paragraphs. Thanks for drawing > that up. > > From reading the Stachiw book, here are the problems I spot: > > 1) You have an O-ring grove on the main pressure bearing surface. > This looks to be taking up at least a quarter, if not a third of > the pressure bearing surface. This will lead to the Acrylic > extruding into the O-ring grove when it is under pressure. > This will lead to stress fractures along the trim. While > this probably won't kill you when it starts, it will mean > replacing the view port lenses earlier than expected. > > 2) The edge of the dome. As the pressure on the face of > the dome increases, the base will expand. This may > push the thin point edge of the dome in to the gap > between the view port seat and the retaining ring. All > the localized pressure build up on the edge may cause > stress fractures on the outer lip. Which will result > in replace the dome sooner than expected. > > 3) The inside rim extending up inside the dome. The > dome contract under pressure, shrinking is size in > slightly extruding into the cabin. I would be concerned > that the dome pressing against the inside rim may cause > it to deform and start to suffer from notch cracking. > > 4) The O-ring on the inside rim. This is another area > which notch cracking may occur. > > 5) The lip of the dome. The type of dome you've drawn > is a sectional spherical dome. These can come with two > types of lips (according to Stachiw), conical or squared. > I don't see anything about the style of lip you've drawn > on the dome. > > You have three seals, the outer most isn't effective > since water can leak in view the retaining ring and > the frame. The metal retaining ring looks expensive > to manufacture, and looks like it will eat expensive > view port Acrylic. > > This could be designed to just use one O-ring and be > much simpler. > > On top of this you've got 3 extra hull penetrations which > hold the retaining ring on. I'm assuming this is some > think you are supposed to use to release the view port? > You have to push these three things out of the hull, > against outside pressure, if you are successful the > hull starts floating before you are ready to exit. > > What if one of the pins jams, catching the thread on > the O-ring groove? If you've already successfully > removed a pin, then you have no way to stop the flooding, > no way to finish removing the dome, no way to escape > from a submarine which is flooding. > > If you start preparing for a wet exit by removing a > pin causing the hull to start flooding, then whatever > emergency which prompted the decision for a wet exit > goes away, you can't cancel the wet exit now, you > must follow though and abandon the sub. > > So, in short, this is going to be expensive to make, > it's probably not going to facilitate a wet exit when > the time come, it's probably going to damage the dome > over time causing it to start cracking and need replaced > long before it's scheduled maintenance. This design > could be improved by making it much simpler: > > - view port frame could be made cheaper and better > using less cuts and eliminating all (expensive) curved > cuts on the cross-section. > > - Use one O-ring, instead of two O-rings and one gasket. > > - Don't add the extra three thru-hulls/flood-holes. > Design it like a hatch, fasteners on the inside, not > outside. > > - Use a standard lip for a sectional spherical dome. > > > You really need to read the Stachiw book when designing > anything related to view ports. Compared to the cost of > making a view port frame and acquiring the acrylic dome, > the Stachiw book is very cheap. > > Cheers, > Ian. > > -----Original Message----- > >From: Brent Hartwig <brenthartwig@hotmail.com> > >Sent: Aug 30, 2008 1:49 AM > >To: PSUBSorg <personal_submersibles@psubs.org> > >Subject: [PSUBS-MAILIST] Wet Exit Removable Front Dome CAD Models > > > > > >Greetings Subbers,Jame Frankland and I spent a fair bit of time discussing and working up ideas for his removable front dome this last winter. I've wanted a hatch type configuration from the start. But first we needed to work thru the concept of copying some features on Nemo's front dome first. So we would like your opinions on the last model I worked up of are combined ideas at that time. I've not been available to refine the models until now. > > > >As it is in the below link to the models and drawings, I would like to add more thickness to the seating ring. Also we might need to make some changes to make it easier to fabricate, and size things to easily available materials. > > > >I've been informed that O-rings used to seal acrylic viewports is perhaps not the best idea because of perhaps stress concentrations in the small area the acrylic touches the O-ring. To deal with that issue I've been thinking about doing some FEA work on two new configurations. One being to use one large soft O-ring for the domes bottom surface to seat on. The other to have two smaller soft O-rings under that said surface. Any thoughts. I have one more sealing configuration, but I'll need to work up a model to better define it. > > > >And yes I'm aware that the dome James now possesses, has a vertically machined surface on the outer perimeter. > > > >http://www.frappr.com/?a=viewphoto&id=2384531&pid=10393161 > > > > > >Your resident possibility thinker ;)' > > > >Regards, > > > >Szybowski > > > > > ************************************************************************ > ************************************************************************ > ************************************************************************ > The personal submersibles mailing list complies with the US Federal > CAN-SPAM Act of 2003. 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