Originally Posted by Brent Swain
How do they design pressure cans to take the pressure? Not Mikes drum skin, flat ,supported by the edges, shape. Check the bottom of pop cans, beer cans, aerosol spray cans, and some propane bottles. They are concave , taking the pressure in compression, on an arc , the same way origami hulls take the pressure. You don't see flat, drum skin type bottoms on such pressure containers, for good reason. Nor do you see framing..
....................... the same way origami hulls get their strength from shape.
They have absolutely nothing similar to a boat hull. Not the shape nor the loads. Forget drink cans and gas bottles we are talking boats here.
Brent you have been told before why pressure vessels are invalid comparisons to boat hulls. Engineering isn't a belief system if you come up with an idea you have to show it's valid. Just saying something repeatedly doesn't make it a fact.
Pressure vessels are a completely different scenario in scale, shape, relative plate thickness and in the level of restraint of the ends. They are also carefully designed for their purpose that includes the end cap shapes. End cap shapes resist buckling but they bear no resemblance to the shallow curves of a boats lines.
In a metal boat hull a huge amount of reserve strength is thrown away if the plate cannot ultimately form a membrane under large strain. If you have tension of one side and compression on the other there is a large amount of material contributing very little to resist collapse. But pre-compressed tension members make this even worse and that's why your designs are so weak for the material they use and why a small amount of additional material added sensibly to your design adds a large amount of strength.
This is a long way from the marketing hype claiming extra strength with less material. Just a classic case of the emperor’s clothes.
Here's Bernard Moitessier's steel sailboat "Joshua". But Joshua was extensively transverse framed so Brent was misinformed again.
The damage at the turn of the bilge is from the plate stretching between the close transverse frames as the hull impacted on a rocky shore. You can see that where blows hit the transverses no damage occurred, where the blows struck the plate ( repeatedly) the plate has stretched between the transverses absorbing the impact energy, the transverses also limit the extent of the damage.
Stretching is significant because to stretch the plate past yield it must be in tension. You cannot develop tension without being able to develop a membrane stress by restraining the plate with supporting structure. Buckling collapse uses significantly less impact energy.
You can see how close the transverse frames are. Gringo mentioned before was also extensively transverse framed with a similar transverse frame spacing as Joshua.
Steel is immensely tough but you have to design with it properly to get it's full strength. If you want to get full tensile strength of the plate in can only develop that in TENSION !