RE: [PSUBS-MAILIST] Wet Exit Removable Front Dome CAD Models

[<jonw@psubs.org>]

Ian,

Thank you for taking the time to provide that detailed explanation.  This is a good illustration of why we simply can't dream things up and believe they will work just because they look clever.  Your last point is spot-on and similar to ones I have made in the past.

Brent,
Like most of us, you have a limited budget to work with.  Trust me, you're in good company.  Putting your money toward the K250 hull first, seems like the path I would have taken as well.  However, your attempt at designing thru-hulls and sealing gaskets is premature given that you do not have expertise in this area.  I suspect Ian spent alot of time reviewing your drawing and then going through Stachiw's book to illustrate relevant points against your design.  I also suspect that most of us simply don't have the time to do that kind of research for everyone that thinks they have a good viewport design, which is why you typically see the "buy-the-book" short answer.  It's not that people are being intentionally difficult to work with, it's because the time involved to get it right is not trivial.  So you have your K-250 and can't afford Stachiw's book yet.  No problem there, I'm sure there are lots of things that you have to work on with the rebuild before even getting to the issue of viewports.  When you do have $200 and can purchase Stachiw's book and read it, then you will have a better understanding of current technology, why stachiw suggests designing things a certain way, and can proceed to ask questions that most of us can address since you'll be able to provide reference to the book section you are inquiring about.  Viewports and attaching them to a hull is not a subject to be taken lightly.  Stachiw spent his life working in this area and that work was so good that it became the standard for ABS and ASME.  Mind you, it's not "a" standard, it is "the" standard.

As you read the book, you'll become aware that Stachiw himself never suggested that something better could not come along, or that existing technology could not be redesigned, or that other designs could not be effective.  However, he did say that any such new or redesign must be thoroughly thoroughly, and in many different configurations and settings before it could be assumed to be safe.  That takes time, money, and other resources that are clearly beyond those of us who cannot afford a $200 book.  On page 1035 of Stachiw's book, he makes an excellent argument for home-builders not to "reinvent the wheel" when it comes to viewports and thru-hull design.

"It is worth remembering, that since its inception in 1977,
the Standard has maintained a perfect safety record over
-14.5 to 20,000psi...pressure range in hundreds of different
manned and unmanned applications.  It would, therefore, be
foolhardy to ignore the guidelines for acrylic window
installations in pressure vessels for human occupancy
presented by the standard." 

Two people in Michigan did not heed this advice and went on their own.  They were engineering college graduates after all.  Read http://www.psubs.org/accidents/seaker100.html to see what their experience was.

Jon






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