In the Dr Seuss book Oh The Thinks You Can Think! there’s a page that reads:
You can think about
Kitty O’Sullivan Krauss
in her big balloon swimming pool
over her house.
It’s accompanied by a picture of an inflatable swimming pool floating in midair, tethered to the ground with a rope.
Which got me thinking: could you actually build a swimming pool that floated in the air like a balloon? I know that the lifting power of hydrogen/helium/whatever is limited and that water is really very heavy. I also know that finding lightweight materials durable enough to hold enough water to swim in would be pretty hard. But can it be done? I don’t have the technical knowledge to work this out.
For the sake of argument let’s ignore issues like stability in crosswinds and suchlike. Also, we’re not talking an Olympic-size pool here; just something deep enough to swim in - say at least three feet deep, three feet wide and 12 feet long - so, what, 108 cubic feet of water minimum.
One litre of helium has a buoyancy of about 1.1 grams. (Hydrogen is a little more buoyant, but rather flammable.)
Let’s convert your 108 cubic feet to 3 cubic metres, for ease of calculation. That weighs 3 tons.
Allow half a ton for the pool structure itself (I think that would be feasible with some fancy lightweight carbon materials), you need a lifting power of 3500kg.
So you need 3500/0.0011 = 3,180,000 litres of helium, or 3,180 cubic metres.
That’s a cube with each side just under 15 metres long, which would allow plenty of space for a small pool on the top face, plus a nice sunbathing area all round. Keeping it stable might be a problem though.
I’ll leave it to someone else to work out how thin the walls would have to be to make a 15-metre cubic structure weigh half a ton or less…
Actually I’ll have a stab at it. The 15-metre cube would have a surface area of 1350 square metres.
To weigh 500kg it needs to have a mass of 0.37kg per square metre.
Aerogels can have a density of just 3kg per cubic metre, so you could have 10cm thick aerogel walls for your cube. Unfortunately, I doubt aerogel is very helium-proof, so you’d need some kind of thin impermeable coating to stop the helium leaking out. Then of course you’ve got to build a container for your water on top.
In summary, it’s going to be tricky. How about a floating hot tub?
I am reminded of a story by the people who made Up - they looked into how many balloons it would really take to lift a house like that, discovered it was something like 27.5 million, and decided to forsake authenticity and just draw “a lot of balloons”.
I just wanted to thank you for this thread. Without it, I never would have realized that the version of “Oh the Thinks You Can Think” that I’ve been reading my son is actually abridged - it never even mentions Kitty O’Sullivan. I’ll have to go out and get the full version.
True, but the figures are pretty rough and ready, so what’s an extra 80kg or so?
(You would have to take into account the weight of the person, of course - displacement doesn’t make the person weightless. Unless of course you meant that you could put less water in the pool, to allow for the volume taken up by the person?)
I mean that if I slide into a pool that is barely containing the water, I’m going to displace some of it over the side. If I’m not displacing anything, you’ve spent too much weight on walls that aren’t holding any water in.
Yebbut… unless you drop into the pool from above without touching the floating structure, your weight is going to be acting on it causing sinkage first.
