Hi Jay,
That makes sense to me. I would expect some stresses to be applied to the acrylic holes as the bolts try to keep the acylic back as they have pressure applied to them. I'm not a fan of any holes in acrylic like Greg Cotrell, if one can help it. He makes boat wind screen replacements constantly, and most of them have the cracks in the original starting from a drilled hole. He said if one must dril a hole, that he would drill the hole over sized and install a rubber bushing in the hole, plus rubber washers on both sides to allow the acylic to be able to expand and contract as well as better deal with vibrasion.
Just from by personal experience of drilling acrylic in the past, I find it very easy to have small cracks appear when drilling. So if you have a lot of holes to drill, what are the chances you will not have any tiny cracks. I've never drilled cell cast acrylic so perhaps it's far better to drill.
Your resident pipe dreamer ;)'
Regards,
Szybowski
From: bottomgun@mindspring.com
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Delta Sub Front MBT Windows
Date: Wed, 3 Sep 2008 22:55:01 -0400
Brent,
You made me think of an old engineering practice to see where stresses were in a structure such as an arch. They would cut a model silhouette of the arch out of thin acrylic and then apply stresses to it that would model the anticipated loads. When the plastic arch was viewed with Polaroid lens, the stress patterns would be revealed in the plastic. From various samples we fooled with and associated images, I would expect that you would see residual stresses in Karl’s failed ports and there would be quite a few around the bolt holes.
R/Jay
Respectfully,
Jay K. Jeffries
Andros Is., Bahamas
Talk sense to a fool and he calls you foolish.
- Euripides (484 BC - 406 BC)
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brent Hartwig
Sent: Wednesday, September 03, 2008 1:08 PM
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Delta Sub Front MBT Windows
Hello Jay,
I was talking to Greg Cottrell about this same matter several weeks ago, and he was kind enough to give me some of his take on it. He also thought/knew that the Delta's main pressure hull viewports having holes drilled thru the acrylic to attach them was pre-spec as you said and have them grandfathered in. He also said that they wouldn't be allowed to change them now if they wanted to keep ABS certification. Unless they had loads of money to get the whole sub re certified. That didn't make total since to me. I would think they could just deal with the viewport assemblies and how they are installed, as well as do some new calcs for that. But not have to redo all the calcs and what not for the whole boat.
The main pressure hull view ports and the front main ballast tank acrylic windows all have the attachment holes drilled in the acrylic from what I've seen. The windows in the front most part of the sub are part of the free flooding front MBT, much like the much thinner acrylic dome over Idabel's large front dome, that acts as the front MBT. Where do you think Karl got part of that idea from. ;)'
We can also see in a couple of the pics below that the Delta has five small viewports mounted in it's front main pressure hull head.
I was talking with Karl about the two viewports he had fail, one on Idabel and one on C-BUG, that had holes drilled in the acrylic to attach them, that I had read about, and had wondered if the holes were the cause of the failures. He said no, they failed for other reasons that had to do with the metal structures that were around them not supporting them evenly. He has since changed the design of the lower front flat viewport. This doesn't mean that drilling holes in acrylic is a good idea, in my opinion. It's just a interesting piece of data to add to are data.
http://www.frappr.com/?a=viewphoto&id=2384531&pid=10409653
http://www.frappr.com/?a=viewphoto&id=2384531&pid=10409648
Your resident hippy dreamer ;)'
Regards,
Szybowski
|