He's swimming on the surface. That bag would be too buoyant for diving.
A modern steel SCUBA tank is typically pressurized to 200 bar, or about 3000 psi, making it 200x more useful than a bag. An inflatable ball is only inflated to about 0.5 bar/8 psig, human lungs are only capable of about 0.1 bar/2 psi. This would be about as useless underwater as one of those little one-liter bottles with integrated mouthpiece that scams show being inflated with a bicycle pump...
Still cool to see swimming like this depicted in 800BC! Puritan attitudes towards swimwear as well as imperial navies conscription of non-swimming sailors seem to have caused us to imagine swimming as a modern activity that we do better than anyone in history, but I expect that people throughout history did lots of swimming.
I also find it interesting that he's depicted wearing a helmet, I wonder if that's to identify that "this guy's an Assyrian foot soldier" or if they actually swam in their helmets!
Modern swimmers probably are better than anyone in history. An optimal front crawl stroke technique isn't intuitively obvious at all. There have been significant improvements just in the last few decades.
https://en.wikipedia.org/wiki/Front_crawl#History?wprov=sfla...
> The "front crawl" style has been in use since ancient times. There is an Egyptian bas relief piece dating to 2000 BCE showing it in use.
My idea did not work out as planned. At the surface I was able to breath through the hose but once I tried to "dive" down I found that drawing a breath was difficult. At the full depth I could not draw a breath. I told my father later on (who was an engineer) and he explained the physics of water pressure.
"Snorkels constitute respiratory dead space. When the user takes in a fresh breath, some of the previously exhaled air which remains in the snorkel is inhaled again, reducing the amount of fresh air in the inhaled volume, and increasing the risk of a buildup of carbon dioxide in the blood, which can result in hypercapnia. The greater the volume of the tube, or the smaller the tidal volume of breathing, the more this problem is exacerbated." —https://en.wikipedia.org/wiki/Snorkel_(swimming)
For a long snorkel, you would want to exhale through your nose.
These irk me too! The pictures never mention that the hand pump in them, isn't a bike pump at all, it's a high-pressure pump that you will have to pump for nearly an hour. I see these constantly in the "suggested products" when shopping for any diving kit on amazon.
First you don’t normally do ultra slow deep breathing with scuba gear which can increase the amount of oxygen extracted. Next the volume of scuba tanks isn’t that high normally and you lose reserve capacity. My guess is up to 5 minutes of air in a bag is probably possible which could be a quite a bit if their pearl diving or something.
On the other hand it could simple be an inflatable bag useful as a flotation device.
The real problem is diving, rather than floating on top of (or more likely underneath) the bag, as others have pointed out.
As a sanity check 6l of air per minute x 5minutes is 30l which is about the size of your torso. Assuming that bag started that size and got completely emptied it’s about right. The volume would decrease rapidly with depth but the available oxygen per breath would increase to compensate.
Unless you have something specific to correct?
https://www.navsea.navy.mil/Home/SUPSALV/00C3-Diving/Diving-...
But I've also seen former military divers who had relatively high gas consumption. Some units mainly use closed circuit rebreathers or surface-supplied gas where breathing rate doesn't matter.
It’s also one of the reasons I was asking for examples as I assumed you where making assumptions that didn’t apply.
Anyone can extend breath hold times at least a little by hyperventilating first to drive down CO2 levels, thus surpressing the urge to breathe. That can be dangerous underwater as it becomes easier to go hypoxic before the urge to breathe gets overwhelming.
https://pubmed.ncbi.nlm.nih.gov/17274316/
I am pretty well aware of what applies here.
>That can be dangerous underwater as it becomes easier to go hypoxic before the urge to breathe gets overwhelming.
Again true on both counts but irrelevant, there is no reason to suppose people in 800BC where average divers. Pearl diving goes back to ~2000BC so demonstrating a very long tradition of people pushing these limits and it’s exactly the people pushing such limits that might try bringing an air supply underwater.
Sure this depiction is almost guaranteed to be a floatation device, but you build something like that and spend your life around water and people are going to try stuff.
> Unless you have something specific to correct?
Firstly, how would you bring the highly buoyant bubble of air underwater, in a controller manner?
But let's say, for the sake of argument, that you could. Even though the volume of the bubble would indeed decrease with depth (e.g. it would halve at 10m), the volume of each breath would remain roughly unaffected by depth. This is the reason scuba divers deplete their air supply faster the deeper they go.
The amount of available oxygen per breath is irrelevant. Even at sea level the exhaled air is about 16% oxygen (down from 21%). Giving the body access to more oxygen per breath won't make the air supply last longer[*].
[*] Interestingly, there's a point at which oxygen becomes toxic. The circumstances in which this happens is well outside the parameters of this discussion, however. https://en.wikipedia.org/wiki/Oxygen_toxicity#Underwater
-Incidentally, in the survival suits we wear when helicommuting in the North Sea contain a rebreather device - which is simply a small bag in the suit's lining with a mouthpiece and a valve.
The idea is that when getting underwater is imminent, you take a few deep breaths. When you exhale into the bag, you can then draw the spent air back in for another gulp or two of air.
The idea being that in a couple of breaths you'll either be in the clear or dead - so a couple of extra breaths is all you realistically need. (Ever the cynic, I suspect part of the reasoning behind it is to keep you busy and un-panicked in your last few seconds alive, but anyway...)
As to available oxygen, removal of CO2 is major limitation in the long term and that’s limited by partial pressures so having more available oxygen doesn’t help in the long term. However, the world record for holding your breath is 22 minutes on pure oxygen so if we are talking a 7 minute vs 12 minute dive CO2 is going to be irrelevant.
Edit: “47% trunk and neck” so 40% torso would be 75kg and 165lb seems reasonable as a smaller person would also need less air.
Sorry it took a while to respond; I got rate-limited this morning.
I never realized it was ambiguous, but the image shows roughly chin to balls so whatever term you want for the longer one. https://twitter.com/FedeItaliano76/status/143529525743702835...
> Another possible explanation for the above scene is that the soldier is helping himself to float by blowing into the goatskin, which is therefore a sort of floating device.