Re: [PSUBS-MAILIST] hull and glass

Mike,

There is no "good" thickness. You need to design in the REQUIRED thickness according to your calculations.

Not all parts of a sub are the same thickness. I'm building a K-350 and it has a .250 inch thick hull with .375 thick end caps. The conning tower is also .250 inch thick, but the transition collar that joins the conning tower to the hull is .750 thick. It's an area of high stress. K-350 is tested at 500 feet and is man rated to 350 feet. I must add, the hull has internal framing also. That's an important part of the structure. If your thinking of 1000 feet, all of this changes drastically.

As far as what type of steel, A-516 grade 70 is recommended because of it's ease of welding and it's pressure vessel quality. I believe it also has some properties that make it better for cold water situations, but don't quote me there.

Plexiglas thickness also depends on the application. It depends on the viewport diameter and the subs depth requirements. My 16 inch viewport is 2 inches thick. The overall diameter is the lens is sixteen inch but the actual view port diameter is about 12 inches because of the large backup lip required to support the Plexiglas lens. All of this, and far more, is covered in a publication called PVHO, Pressure Vessel for Human Occupation. I suggest you get a copy if your designing from scratch.

There is another way of building a sub if your not really set on YOUR OWN design. Purchase a set of K-250 or K-350 plans and alter what you feel comfortable with from there. Believe me, you'll have plenty of chances to design in your own options but you also have the peace of mind that what your building has been tested and proven many times.

Don't get in over your head designing something you won't feel safe in. You will have a bunch of money invested in a sub by the time your finished. It makes no sense to build something that you can't use, or can't sell to anyone late on. Even worst, it may get you killed. Do your homework.

Again, good luck, Dan H.

----- Original Message -----

From: Michael Fodor

To: personal_submersibles@psubs.org

Sent: Monday, March 17, 2003 4:09 PM

Subject: Re: [PSUBS-MAILIST] hull and glass

Thanks Dan I appreciate the help I will have to check the archives for further info, is there a good thickness for the steel ? the plexi-glass ?

Thanks
"Dan H." <JMachine@adelphia.net> wrote:

Mike,

A thousand feet is deep for many PSUBS. My material of choice is "tried and true" Steel. Pressure vestal quality steel. It's easy to find and not to bad to work with. There's a lot of information available on it too. The extra weight in a sub isn't usually a really big deal since your building it to sink anyway. If it doesn't weigh it's weight in water displaced, you built a surface boat.

To build a steel sub to go a thousand feet of depth though you may be reaching the upper end of weight to PSUB size ratio though. It depends on the overall displacement of the sub your building. With steel, you MUST know how to weld. Even if you farm out most of it, there will still be many small welding jobs that you have to do along the way.

Plexiglas G is the material of choice for viewports. It too is easy to come by and work with. Do some research in how to machine and anneal it though. There is good data available on it also.

You may consider designing 2.5 safety factor for a collapse depth. You should do an unmanned test to 1.5-2.0, just to prove the hull.

I don't know about fabric over any kind of frame. It's not my area.

You will probably have to have frames in your hull to keep roundness no matter the material. Your hull must be concentric. You can't have any flat spots or even out of roundness. You can't be out of round anymore then half the hull material thickness.

Good luck,

Dan H.

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