Is this homemade diving bell story credible?

June 26, 2006 10:06 PM

A friend thrice removed claims that as a kid, he used to shut out the world by inverting a trash can, tying a few cinder blocks to it, and submerging himself in his parents' swimming pool. I dig this story...

...but upon further reflection I think it's crap. The number of cinder blocks would be prohibitive, execution tricky, buoyancy overwhelming.

The first degree friend who told me this story disagrees. She shares my skepticism, but, as friends do, she directs it at my reasoning. Boyle, Archimedes, arithmetic, stories about tech diving lift bags, conservative assumptions--all left her unmoved. She believes; I am an infidel.

In the spirit of this post, I appeal to mefites. She and I share a need to be pompously, geekily correct on technical issues. Help us settle the argument and in a way we'll both be winners. Although in another, more accurate way, one of us will be the winner.

Some constraints:

--The story as told said "a few" cinder blocks. The 2nd degree friend says four.

--Let's say it's a 32 (U.S.) gallon plastic backyard garbage can.

--The storyteller implied that he stayed down long enough to have some thoughts and sulk.

--Let's say the kid was 80lbs-95lbs and 10yrs old.

--No more information is available, but we have agreed on other assumptions if people need them.

p.s. there's no reason for this to get back to the storyteller. This is between my friend and me. And some 30,000 askmefites.

posted by Phred182 to Science & Nature (34 answers total)

You could totally do this. The only real problem would be balancing the "diving bell" so it submerged straight. Tie three cinderblocks to the trash can rim, spaced evenly apart, make sure the lines didn't get tangled, and the can would go down just fine.

Besides -- define "submerged." The entire trash can? Or just the rim under water, allowing the kid to swim under and in? That's even easier.

At age 10, I turned an Estes model rocket kit in a shoulder-fired, rocket-propelled grenade that was frightenly accurate. Don't ever underestimate the engineering skills of a determined kid with plenty of time on his hands. ;-)
posted by frogan at 10:18 PM on June 26, 2006 [3 favorites]

Response by poster: We're gonna define submerged as fully under water. Otherwise it kind of defeats the run away, hide and sulk thing.

I picture that scene from the Graduate.

Your last sentence may become my motto.
posted by Phred182 at 10:24 PM on June 26, 2006

I love this question.

I did it with a big 10-gallon bucket (using my hands to pull it down, no weights) as a kid. Wait, 10-gallon? That kind of big white bucket that restaurant pickles come in and your dad used to wash the car. I remember that it was actually remarkably stable underwater, almost like magic.

Or maybe I just remember it that way. I remember how loud my breath was, just like Darth Vader, the way it echoed in that little air chamber. I suppose it was dangerous.
posted by _sirmissalot_ at 10:27 PM on June 26, 2006 [1 favorite]

You know, it might not have been remarkably stable. I think my memory is totally faulty here and that there is a chance, significant if not overwhelming, that I'm sentimentalizing the whole episode. Your friend may be suffering from the same weakness. It is a good story nonetheless.
posted by _sirmissalot_ at 10:32 PM on June 26, 2006 [2 favorites]

32 gallons of water = ~121kg

human density very close to that of water

buoyancy = ~121kg - ~36kg (80lbs, best case) = ~85kg

typical cinder block = ~12-15kg (let's assume 15, best case)

concrete only ~2.4x as dense as water, so you're only getting ~58% of the weight when it's under water

15*.58= ~8.7kg downforce per cinder block

85/8.7=~9.8

So you'd need, at the very least, 10 cinder blocks. But yeah, you could do it, and I bet the oxygen wouldn't be too much of a problem.
posted by trevyn at 10:39 PM on June 26, 2006

Bear in mind that the container can be only half full of air, enough for your head and shoulders to be in air but the rest of you wet.

If it's not a full sized can, and it's not totally filled with air, it could be done.

As a kid I used to do a similar thing with an oversized bucket.

I enjoyed it immensely, the confinment and filtering of the light were relaxing, but my sister - a claustraphobe - would freak out and `rescue' me.
posted by tomble at 10:45 PM on June 26, 2006

I don't see why you couldn't do this. Presumably you could add just the right number of blocks to make the weight very slightly stronger than the buoyancy. Then it would stay underwater, but also be really easy to maneuver. (And you wouldn't get trapped under it.)

But:
1. How many blocks would you need? (on preview: wow, quite a lot)
2. When do you attach the blocks? If you do it on land, then you need to somehow carry the whole assembly over to the pool. If you do it in the water, then you have to hold the block up as you tie it. (although the pool stairs might help here)
3. How long would it take to do all this? Seems like a lot of effort just to be sulky.

But hey, maybe. Doesn't sound unreasonable to me.
posted by equalpants at 10:58 PM on June 26, 2006

32 gallons is about 120 liters. Archimedes' principle, states that a body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid.

So in this case the upwards force would be 120 Newtons.
For the trashcan to actually sink all the way, you'd have to be putting more than 120 newtons of force downwards. One kilo of weight pulling down equals one newton,(on preview: oops, not in water) so that would be a lot of cinderblocks. I don't know exactly how much a cinderblock weights, but there's no way that "a few" weigh 120 kilos.

Now of course I haven't taken into the account the displacement of the diver's head, but even with that it would be more than four blocks. Are you sure that it was a 32 gallon can? It's more likely that it was a much smaller container.

On preview: ok, let's say 15kg per block, and a container only half full of air, that's only 5 blocks. Totally possible, I doubt that the cinderblocks he used were as heavy as that, but if the container was smaller then a full sized trash can you could do it easily. A vertical shape like that would be fairly stable and you wouldn't have to be all that precise with how the ballast was arranged.
posted by atrazine at 10:58 PM on June 26, 2006

Are we assuming that he just dumped the trash can, rope and cinder blocks into the pool and hoped for the best?

If it was me I'd start with the blocks on the bottom of the pool, slack in the ropes so that the bin wasn't fully submerged, and then tighten the ropes bit by bit somehow.
posted by AmbroseChapel at 11:02 PM on June 26, 2006

Upon further thought, maybe it could be a bit of an exaggeration? Maybe he used to do the same thing tomble did, but when telling the story, he found that "I used to tie cinder blocks to a trash can and sit at the bottom of the pool" was more effective than "I used to submerge myself in the pool using a bucket, and one time I tried to use a trash can but it didn't really work, and then later I had the idea of tying a cinder block to the trash can, but I couldn't really get that to work either."
posted by equalpants at 11:04 PM on June 26, 2006 [1 favorite]

Eck, got that backwards...best case would be 95 lbs, not 80. So 9 blocks minimum. ;)
posted by trevyn at 11:07 PM on June 26, 2006

the only flaw i'm seeing in this is the amount of oxygen he would have ... how long would this really last him?
posted by pyramid termite at 11:13 PM on June 26, 2006

In terms of actually getting into the pool with all this "tied on," if it were me I'd lay the garbage can on its side, crouch down and get my arms into it / crawl into it a little, then tip it onto me and lift it up over/onto my head. You could easily walk carrying the weight of a few cinder blocks straight down into the water. Don't bang your knees on the blocks.... but it'd work.

Sensory deprivation in the ol' parents' swimming pool is safer & longer with SCUBA gear and the right weight belt. While the trash can thing is plausible, it wouldn't be any fun/relaxation whatsoever. Unless you like darkness, a feeling of being trapped, and the stench of your own compartmentalized breath.
posted by scarabic at 11:17 PM on June 26, 2006

Yeah i have difficulty figuring out how exactly you would attach the cinderblocks to the trash can. If you tie it all together at the begginning you have a massively heavy, unweildy contraption that would be nearly impossible for a kid to get into a pool. If you do it after you would have to do it one by one, unbalancing the trash can by attaching each block. Also, what were these cinderblocks attached to? I think those handles might actually break under such a force. Or did he drill holes into the metal trash can? This story is looking more and more improbable.

On preview: You could easily walk carrying the weight of a few cinder blocks.

You could carry 10 cinderblocks and a trash can at the same time when you were a kid?
posted by sophist at 11:21 PM on June 26, 2006

Not only did I do this, but I added an air compressor attached to rubber tubing pumping air down to the bottom of the deep end.
posted by planetkyoto at 11:34 PM on June 26, 2006

You have to add the weight of the kid to the downforce too, assuming he is holding onto the can. That has to be good for a few cinderblocks.
posted by Lame_username at 2:04 AM on June 27, 2006

If I were to do this, I would use two trash cans fastened together at their bases, so that when the first is inverted, the second is sitting right side up on top of it. You would need to drill holes and use bolts and rubber gaskets to make a watertight sea.

Loosely attach a 6-7 foot rubber hose so it is running up the side of the "rightside up" trash can, with the topmost foot or two attached so it is directed inside that trash can. The hose should be attached down the bottom of the assembly all the way to the rim of the upside down trash can.

Begin filling the upper trashcan with water by sucking on the tube and getting a siphon going. As that trashcan fills with water the whole assembly sinks. Operator must stand there to ensure nothing tips over, but as the can fills up that should be less of a problem. At the opportune time the operator ducks underwater and pops up inside the trashcan. Sulk as required.
posted by stupidsexyFlanders at 2:06 AM on June 27, 2006

If you accomplish this task don't stay under very long. When the oxygen runs out you won't be gasping for air, you will just get light headed and then . . . . A plastic bag and a rubber bag is considered one of the least painful ways to go, and this could easily become the same thing if you are not careful. Also, does that pool have a vinyl liner? Even many in-ground pools have them these days and I don't think you want to be lobbing cinder blocks onto one of these.
posted by caddis at 4:27 AM on June 27, 2006

The storyteller implied that he stayed down long enough to have some thoughts and sulk

I don't have too much to add to what has already been said, except to point out that time passes very, very slowly when you are ten years old. I would guess that he would have needed about 1/10th as long as an adult to do this.

I vote for "more or less true, but possibly elaborated/misremembered a little bit".
posted by teleskiving at 4:30 AM on June 27, 2006

Sounds like a diving bell to me. Make rope "handles" on each handle of the trashcan, and then tie another fairly long rope through the two handles and a bunch of cinderblocks. Put trashcan in the water while leaving the cinderblocks on the deck. Now chuck the cinderblocks over one by one. At a certain point the whole thing will get pulled over the side and into the water so getting the timing right here might be tricky, but the weight of the cinder blocks would pull the already-correctly-positioned trashcan right under water.*

* Note to any kids thinking of doing this: It would also royally screw up the deck and pool liner, so move on to something else. Try a game of Chess instead.
posted by jwells at 5:16 AM on June 27, 2006

Oh, and it depends on if they were using a cinder block or concrete block. Concrete blocks can weight up to 18kg (if you believe wikipedia). Assuming that and a water weight of 3.785kg/gallon, the trashcan could be up to 19 gallons before he needed more than 4 blocks, 23 gallons for 5 blocks, 28 for 6, and 33 for 7 blocks. How a 43kg child could move 7 18kg blocks is beyond me, even one at a time. It'd be better if there were an anchor at the bottom he could thread a rope through and then pull on the rope and draw the trashcan down. With a pulley (tree branch, etc.) he might be able to do that.
posted by jwells at 6:00 AM on June 27, 2006

I'd love to see a question like this on the MCAT...
posted by greatgefilte at 6:36 AM on June 27, 2006

I hope that garbage can was clean. I think it would be hard to find solace inside most garbage cans I have smelled.

I too suspect that the physical challenge of maneuvering the cinder blocks and garbage can would be difficult for a 10 year old boy. One block at a time I guess, all neatly lined up at the edge of the pool. Of course the easy way to accomplish this is to submerged the can largely flooded, add more cinder blocks beneath the surface and then pump air in. It would be interesting to see how quickly he responds with a method for such a small person to handle such large weights, although if this is a big fib he may have already worked out that part of the story as well.
posted by caddis at 7:53 AM on June 27, 2006

I think a lot depends on how far the trashcan was submerged and how the cinderblocks were tied.

A lot of folks here (me included, at first) seem to be assuming that the trash can had to sink all, or at least most, of the way to the bottom.

I don't think that's the case. A 10 year old kid is likely to be very happy inside a 'diving bell' bobbing around on top of the water. I know I had a lot of fun with tipped-over canoes and stuff like that... surfacing with my head above water, but inside the canoe, was pretty fun.

The simplest solution I can see that a 10 year old could do... start with two cinderblocks and a trashcan in the shallow end. Tie one cinderblock to each handle. Put the trashcan over your body so that you're standing inside it. Lift the ropes and wade into the deep end... underwater cinderblocks won't be that heavy for a 10 year old, especially when your own body weighs so little. As you walk toward the deep end, the cinderblocks will keep your feet on the bottom until the buoyancy of the air trapped in the trash can exceeds the weight of the cinderblocks. At that point, you should be able to release them, and the can should stay nicely upright, floating on the water with the cinderblocks dangling below.

If you want the can to sink deeper, use more cinderblocks, or trap less air.
posted by Malor at 7:58 AM on June 27, 2006

Best answer: * Note to any kids thinking of doing this: It would also royally screw up the deck and pool liner, so move on to something else.

If any kids are reading this, realize that we are just speculating and that actually trying any of this would be A VERY BAD IDEA! You could run out of oxygen very quickly and not notice it. Even upthread when I talked about trying something like this, it was only for a few seconds, I didn't actually go under water, and even then it was a dumb thing to do.

If you want to try breathing under water, see if you can get your parents to sign you up for SCUBA lessons. In a lot of places, your local YMCA will offer this, and it's really amazing.
posted by _sirmissalot_ at 9:06 AM on June 27, 2006 [1 favorite]

I'm pretty sure that you would notice increased concentrations of CO₂ well before you ran out of oxygen. Like breathing into a paper bag.
posted by breath at 9:12 AM on June 27, 2006

By the time you noticed it, it could be too late if you were under water and getting dizzy. Very scary idea actually.
posted by _sirmissalot_ at 9:29 AM on June 27, 2006

What if you exhaled outside of the garbage can, and only inhaled inside the garbage can? I imagine you could stay underwater for a long time without polluting your air source with carbon dioxide.
posted by blahtsk at 10:35 AM on June 27, 2006

What if you exhaled outside of the garbage can, and only inhaled inside the garbage can?

Each time you would do this, though, you would be emptying the air bubble inside the submerged can. Depending on the starting size, you would empty the can and it would sink and tip over.

Make rope "handles" on each handle of the trashcan, and then tie another fairly long rope through the two handles and a bunch of cinderblocks...

My thoughts exactly.
posted by frogan at 11:04 AM on June 27, 2006

Needed:

• 1 Plastic garbage can with hole in bottom
• 1 object that can plug the hole in the plastic garbage can
• A bunch of cinder blocks, lobbed into the pool one at a time
• 2 Ropes
• 1 heavy-duty plastic bag

1. Throw garbage can and cinder blocks into pool, Hole in Garbage can is unplugged.
2. Submerge can, tie it to cinder blocks with 1 rope.
3. Plug hole
4. Get 1/2 garbage bag worth of air, using second rope through cinder block(s) as a make-shift pully AND your own body weight, pull garbage bag of air down to the bottom of the pool. Empty into upside-down garbage can.
5. Repeat for 30 minutes.
6. Sulk for 10 minutes.

Yeah, I could TOTALLY see myself doing this as a kid (if we had a pool, that is).
posted by hatsix at 11:04 AM on June 27, 2006

No, you definitely don't want to do that. You'd run out of oxygen without knowing about it. The carbon dioxide response occurs much more quickly than oxygen depletion in a confined space, so when it happens you have enough oxygen for evasive maneuvers. If you subvert this by putting all your carbon dioxide outside the can, you will certainly run out of oxygen and not notice it, like these kids.

Of course, carbon dioxide poisoning is not to be laughed at either. There's always the chance that you will pass out from it and drown.
posted by breath at 11:12 AM on June 27, 2006

Didn't preview, my response is to blahtsk. Good point, Frogan.
posted by breath at 11:13 AM on June 27, 2006

What if you exhaled outside of the garbage can, and only inhaled inside the garbage can?

Then with each exhalation, you would be emptying the garbage can of air, and filling it with water.

According to wikipedia, the average adult breath is "500 ml to 700 ml of air" and vigorous breathing is "rates exceeding 35 breaths per minute". So picking the easy numbers of 500ml and 30bpm, that's 15l/minute. A half full 32 gallon garbage can would be 16 gallons of air, or approximately 60 liters, so in 4 minutes the garbage can will be full of water.
posted by fings at 11:13 AM on June 27, 2006

Response by poster: I love metafilter--thank you for such great, thoughtful responses. Marking warning as best answer because I neglected to put one in.

My friend wanted to send her ten-year old to do field tests--guess that's out. I suddenly remember doing this with a canoe and it seems we had enough air for a few gasps.

I came up with 9-10 cinderblocks and that the story was an exaggeration at best. She wants to do field tests.
posted by Phred182 at 7:16 AM on June 28, 2006