I recommend that you do not drill the acrylic at all, but rather have a seat and retaining ring arrangement that keeps the bolts through steel only, and the dome flange sandwiched between the seat and retaining ring. I also recommend against using any 1/4" fasteners at all - despite the fact that these may be strong enough for your application, it is easy to overtorque 1/4" bolts with hand tools, and in extreme cases, to twist the heads off. Using larger diameter fasteners reduces the chance of overtorquing, and gives you better shear strength and corrosion resistance. Certainly, design the retaining arrangement to support the anticipated loading from sitting, leaning on, or inadvertently striking the window, but in the absence of any other requirements, I would suggest a general structural guideline of designing an ambient sub for a 1 ATM pressure differential, external or internal.
-Sean
On Aug 29, 2008, djackson99@aol.com wrote:
Hello Carlos
You want something between 4 - 1/4 inch bolts, and 1 - 1/2" bolt every 2 inches. :)
If your flange were on the outside I'd first consider the load. Visualize your sub with the dome on, then turned upside down and filled with water so that the water occupies the same space that air will occupy. How many gallons of water is that? At 8.2 pounds per gallons, how much weight is that? Then multiply by 2+ and get enough bolts to hold that amount.
Consider that acrylic does not like being drilled and it will crack around the edges and holes. Annealing will help prevent that but it is still a failure point so you will likely want to add a ring to spread the load from the bolts.
Since your flange is on the inside, I'd keep the holes size and spacing to a minimum in order to reduce weakening the acrylic. I'd want to be able to support 250 pounds so someone could sit on it, and if you have a ring on the inside to spread the load then 6 - 1/4 inch bolts with big washers would do. I'd also consider the possibility of your ambient sub becoming a 1ATM sub when it makes a fast decent, and I'd think about what will happen if you were to hit something when surfacing like a Japanese fishing boat. If you're using a dry seal like a neoprene gasket, you'll need to keep it compressed enough to keep it from leaking air. You'll also want to make the hole sufficiently larger than the bolt to account for any expansion diference between your acrylic and hull.
If it were me, I'd use Sikaflex; www.sikaindustry.com and glue it in. You'll have to destroy it if you ever want it out again, but if your takeing it out your likely doing so to replace it anyway. I am picking up my acrylic today, and I plan to use Sikaflex to glue it in. No bolts or holes.
Best of Luck
Doug
www.submarineboat.com
-----Original Message-----
From: Carlos Del Valle <carlosd072657@gmail.com>
To: personal_submersibles@psubs.org
Sent: Fri, 29 Aug 2008 9:48 am
Subject: Re: [PSUBS-MAILIST] depth indicator
Hi Doug, I'm also building an ambient sub, re: dome mounting, I have a
1/4" acrylic
dome 22" dia. with a 2" flange. I'm going to bolt the flange from the
inside. How many bolts should I use and how far apart should they be?
I'll wait to hear from you
before I start drilling holes. Also, can I use individual washers for
each bolt or
should I get a support ring, and if so, how makes them?
Thanks, Carlos
n 8/29/08, djackson99@aol.com <djackson99@aol.com> wrote:
> Hmmmm... Not the weight of the sub. It should indicate the depth of the vent
> where the air is released into the surrounding water and likely a little
> deeper since the constant flow of air may add a few psi to the ambient
> cabin. Air at the top of the cabin is at the same pressure as the air at
> the bottom of the cabin where it is vented to the surrounding water. So it
> does not matter where the gauge is inside the cabin.
>
> That also makes the air at the top of the cabin at a pressure higher than
> the water surrounding the top of the cabin. So a hatch in the top of an
> ambient sub seals naturally if it opens inward. Completely opposite to a
> 1ATM sub.
>
> In my case the dive computer is going to ride along outside the forward view
> port. There is no room for it inside and with it outside it will
> automatically start logging the dive when it submerges.
>
> So what are you thinking of building?
>
> Doug J
> www.submarineboat.com
>
>
> -----Original Message-----
> From: David Bartsch <dbartsch2236@hotmail.com>
> To: personal_submersibles@psubs.org
> Sent: Thu, 28 Aug 2008 11:11 pm
> Subject: [PSUBS-MAILIST] depth indicator
>
> In an ambient submarine, if one uses a dive watch type depth indicators
> to give an indication of how deep He is, does this display the actual depth
> or will it be off a little having the additional weight of the sub working
> on it? One of those HMMMM thoughts...
>
>
> David Bartsch
>
> ________________________________
> Be the filmmaker you always wanted to beearn how to burn a DVD with Windows.
> Make your smash hit=
>
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