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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 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 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. Frank D.
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