Hi Frank and Hugh,
I know that feeling of looking at some thing and seeing the weak points. Even if you don't know the engineering specs, if you've seen enough broken buildings or machines you start to see a pattern of failure modes. Your design might not be as balanced (meaning every thing would fail about the same time) as one designed by a qualified engineer. But it will give you more piece of mind.
Also I like to see designs with some tough collision protect added in. Since Frank is adding support ribs he should have a fair bit of collision protection.
Frank made a good point about saving money by buying more steal instead of lead, and adding strength to the hull as well. One thing I would like to add into that is, that having heavier drop weight(s) is a very useful feature if your sub is flooding. So you will have to balance out what you think will work well. But it looks like Frank would of still needed a lot of lead in his drop weights, even if he had used a 1/2" hull. So all I have to say to that is, more batteries, more power Frank. Also you could be the first PSUBer to have electro plated chromed Optima batteries.
TP has perforations? Now I know why I read this forum, I learn some thing every day. ;)'
"The only time my education was interrupted, was when I was in school."
~ George Bernard Shaw
Cheers,
Brent Hartwig
From: hc.fulton@gmail.com
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Newbie
Date: Tue, 27 May 2008 08:23:08 +1200
Frank,
I have to agree with you. If you have the space, use it. Only a fool takes no notice of experience. I was accused of making a structure that had a safety factor of 400:1 but it looked right. As it was one leg of 4 for carrying 6 tons on top and located at a gas station if a car demolished one of the legs it wouldn’t have collapsed. Reminds me of a machine that was made in Germany that kept breaking a component which was a flat bar. The Engineers tried everything. After the last failure they were in a group standing around looking at the machine discussing how it could be fixed when a fellow who was passing poked his nose in and told them to drill a line of holes along where it was breaking. They thought it was a stupid idea but then they had tried everything else so they gave the suggestion a try as they had nothing to lose. Well it never broke after that. They looked for the guy who made the suggestion and found that he was the janitor. They asked him if he had any formal training in Engineering. He replied, “ no but I’ve been cleaning around Toilets for many years and not once have I seen toilet paper break along the perforations!”
I think my biggest concern is distortion of the window seats. I am going to get a guy to do FEA on them. What was the radius on your hatch cover? Regards, Hugh
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of ShellyDalg@aol.com
Sent: 27 May 2008 05:45
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Newbie
Hi Hugh. Although the conventional wisdom says no ribs are needed, I'm not so sure. First off, I cut a big hole in the top for the hatch. To replace the metal, I made the hatch flange 1-1/2 inches thick and put it directly in line with the hull, plus the 3/8 inch thick hatch ring at 6 inches long. I have no "tower" really. The hatch ring sticks up only 1-1/2 inches above the hull, and protrudes 4 inches into the sub. I just had the feeling that with that big hole in there, and the elastic nature of metal, it was a weak spot.
I'm no engineer, but I've got 40 years of welding and general metal working experience and it just seems like it's a good idea. Think of this....the hatch at 24 inch O.D. has 452 square inches. If the pressure is say 18 atmospheres at 600 feet, how many pounds is actually pushing on that hatch?
Next, the actual shape of those steel tubs isn't hemispherical. It's kinda flattened on top. So the pressure pushing down isn't completely compensated by the pressure pushing in from the sides. Also, I've got some big holes where the windows are cut in. Again, I've replaced the metal removed with the window frames and flanges, plus the location is on a more curved part of the hull, but it still creates a weak spot.
I take that whole "hull calculator" with a little skepticism. I know it's based in sound engineering principles, but I'm not sure It takes all the complexities of windows, hatches, metal irregularities and induced stresses into account. I've built a lot of stuff over the years, and I've got a pretty well developed "gut feeling" for what works. Besides, I need more weight anyway, why not use the additional weight to add strength. I've got to add almost a ton of lead to this thing. Steel is cheaper than lead.
|