4 ms·

This is really neat. I probably drew 100 diagrams of submarine designs as a kid. Kudos to him for actually building one (or four for that matter). I'm curious

This is really neat. I probably drew 100 diagrams of submarine designs as a kid. Kudos to him for actually building one (or four for that matter). I'm curious if the 30ft depth limit is simply a practical safety limit (if you remember back to High School Physics, 33ft of fresh water = 1 atmosphere of pressure) or if he actually worked out the limits of the drainage tubing/joints/skylight/other components. It would be cool if he did a technical writeup.

Lost_BiomedE 13y ago
30ft may be a good safety limit, but the total pressure is the atmosphere plus 1 atmosphere, due to the water, equaling 2atm.
- wicknicks 13y ago
  But the additional pressure the sub has to counter is 1atm.
  - mischanix 13y ago
    I'm curious, is that force (2atm:1atm) linear (= 1atm:0atm) or exponential (< 1atm:0atm)?
    - m4rkuskk 13y ago
      It's linear. The surrounding pressure increases by the following: P=γ*h P=pressure (lb/ft^2) h=height (ft) γ=density (lb/ft^3) water = 62.4lb/ft^3 So if he goes down 33ft, the pressure @33ft will be: Total pressure: 62.4x33 = 2059psf (1atm ≈ 2116.21psf)
    - deleted 13y ago
      [deleted]
    - uvdiv 13y ago
      What physically matters is the pressure difference. 2atm:1atm and 1atm:0atm are the same -- they both exert 1.03 kg-force per square centimeter of wall. If you're asking how does pressure change with depth, it's linear for water. The pressure is just the sum weight of the column of fluid above you. Since water is (basically) incompressible, the density is the same at any depth, so, the fluid weight is proportional to the column height. At ~10 meters, it's 1.03 kgf per cm^2 or 1 atmosphere (on top of one atmosphere of air above, for 2 atmospheres total). It's the opposite for air. That's a compressible gas, so density increases with pressure, which makes pressure an exponential function of altitude. A packet of air is compressed by the air above it, which makes it denser (more mass/volume), so that the pressure below increases at a steeper rate.
      - mischanix 13y ago
        Thanks for the explanation. I wasn't intuiting the difference between air and water.
  - Lost_BiomedE 13y ago
    So is it implied that he tests on the surface by creating a vacuum inside the sub?
    - isaacb 13y ago
      Or even easier, just submerge it without a person inside and see how deep it can go.
salimmadjd 13y ago
I also designed a bunch of submarines and wanted to build one for the masses. Until my friends told me I was crazy and I would kill myself. My final design was using scuba tanks to equalize the internal pressure of the sub with ambient pressure at specific depth. This was a clever design but limited it's usefulness to 30f as well. It simplified the construction of the sub but limited its use as it required depressurization following the same rules applied to SCUBA divers. So at 30ft you could be submerged for a while, but any deeper it limited the time you could remained submerged unless you depressurized before surfacing.
- mtdewcmu 13y ago
  The odds of killing yourself with this type of project must be pretty high.

Lost_BiomedE 13y ago

30ft may be a good safety limit, but the total pressure is the atmosphere plus 1 atmosphere, due to the water, equaling 2atm.

wicknicks 13y ago
But the additional pressure the sub has to counter is 1atm.
- mischanix 13y ago
  I'm curious, is that force (2atm:1atm) linear (= 1atm:0atm) or exponential (< 1atm:0atm)?
  - m4rkuskk 13y ago
    It's linear. The surrounding pressure increases by the following: P=γ*h P=pressure (lb/ft^2) h=height (ft) γ=density (lb/ft^3) water = 62.4lb/ft^3 So if he goes down 33ft, the pressure @33ft will be: Total pressure: 62.4x33 = 2059psf (1atm ≈ 2116.21psf)
  - deleted 13y ago
    [deleted]
  - uvdiv 13y ago
    What physically matters is the pressure difference. 2atm:1atm and 1atm:0atm are the same -- they both exert 1.03 kg-force per square centimeter of wall. If you're asking how does pressure change with depth, it's linear for water. The pressure is just the sum weight of the column of fluid above you. Since water is (basically) incompressible, the density is the same at any depth, so, the fluid weight is proportional to the column height. At ~10 meters, it's 1.03 kgf per cm^2 or 1 atmosphere (on top of one atmosphere of air above, for 2 atmospheres total). It's the opposite for air. That's a compressible gas, so density increases with pressure, which makes pressure an exponential function of altitude. A packet of air is compressed by the air above it, which makes it denser (more mass/volume), so that the pressure below increases at a steeper rate.
    - mischanix 13y ago
      Thanks for the explanation. I wasn't intuiting the difference between air and water.
- Lost_BiomedE 13y ago
  So is it implied that he tests on the surface by creating a vacuum inside the sub?
  - isaacb 13y ago
    Or even easier, just submerge it without a person inside and see how deep it can go.

salimmadjd 13y ago

I also designed a bunch of submarines and wanted to build one for the masses. Until my friends told me I was crazy and I would kill myself. My final design was using scuba tanks to equalize the internal pressure of the sub with ambient pressure at specific depth. This was a clever design but limited it's usefulness to 30f as well. It simplified the construction of the sub but limited its use as it required depressurization following the same rules applied to SCUBA divers. So at 30ft you could be submerged for a while, but any deeper it limited the time you could remained submerged unless you depressurized before surfacing.

mtdewcmu 13y ago
The odds of killing yourself with this type of project must be pretty high.