Fascinating, the second image attached to https://twitter.com/FedeItaliano76/status/143532682797161267... is good too -- I'm not settled in that confirming the second hypothesis (surface use), as the Twitter user says, it seems to me to also give stronger weight to the first (under water use).
In this image the 'goatskin' users appear fully clothed in dresses (could they be scale armour or other weighted clothing), only one has a beard. A person without a goatskin appears "above" them (could be behind depending on perspective) and IMO appears to be getting shot with arrows. The "divers" aren't wearing onion-shaped helmets. The goatskins appear to be fixed to the belts on their waists.
One could interpret this as showing underwater swimming to avoid archers.
Perhaps it was an idea, rather than a practiced activity? Maybe the goatskin has rocks in it too, to balance buoyancy? Perhaps the carrying a rock bit was not shown for fear of letting enemies in on the idea!?!
[But yes, more probably a floatation device; fun to speculate though. Would particularly be interested to look at perspective in Assyrian bas reliefs]
Really interesting, would love to hear some Assyrian historians debate this.
The work of submerging air at atmospheric pressure vastly exceeds the potential energy value extractable from the oxygen in terms of ATP. He's using it to float.
I was thinking that as well; it's not going to get you more than a few breaths of air, and it's not going to be easy to submerge with one. Even bogged down with weapons and armor, I suspect it would be impossible to submerge while holding something that large filled with air.
Even if you could submerge it, it would require ridiculous effort to hold it submerged. I doubt one could swim across a body of water with weapons, armor, and a submerged goatskin bag and expect to make it very often.
>The work of submerging air at atmospheric pressure vastly exceeds the potential energy value extractable from the oxygen in terms of ATP. He's using it to float.
he is wearing some armor, definitely head helmet - that allows to balance the floatation, and would be beyond most human capabilities without the goatskin. So he achieves 2 goals simultaneously - extra air for prolonged diving as well as diving while donning some armor. That goatskin is like 20-30 liters - good for several minutes of breathing and those 20-30kg of extra floatation allow for the typical armor/chainmail and weapons.
There is no issues with holding it submerged like other commenters suggest as he keeps it under the body, so the main force of those 20-30kg pushes onto his body up, and if anything it is very easy to belt it to the body so it wouldn't need any hands involvement to be maintained under the body.
There is also no issues with drawing breath as suggested by others as the goatskin is under the same water pressure as his lungs.
If you think there are no issues then try it yourself with an inflatable beach ball and some weights in the shallow end of your local swimming pool. Be sure to record a video: it's going to be hilarious watching you flail around underwater while making no forward progress.
What convinces you it's a working system? Making your enemies, and even your own people, think that you 'can even reach those in fortresses beyond a moat, and even archers on watch won't see you coming' surely has a lot of value.
If you used it as a re-breather then surely the work needed is no greater than the work needed to submerge a lungful of air?
I expect you're right that it's a float (appropriate username is appropriate!) - but the balance point seems likely to me to be a small additional volume of air as well as the lungs full capacity. Otherwise maximum horizontal distance would be attained by exhaling early when swimming underwater - that's contrary to my experience - and large lung capacity would be detrimental to swimming underwater.
I wonder if the scene depicted is much of an action scene then, or if the archer is just there because they're soldiers. I'd imagine swimming with this goat bag is hardly tactically viable in almost any situation.
The divers can not inflate it further once submerged, yet have put their mouths on the container.
Even as a "re-breathing" container, having that reserve of air volume would allow for extended lingering time below the surface, as it would take much longer for the CO2 saturation to become a problem than just a lung full of air.
Thus, this likely served two purposes. 1) buoyancy to counter the weight of armor, and 2) additional time underwater by rebreathing (more) stale air than one can hold in their lungs.
I thought the archers were friendly at first. Then noticed one is pointing their bow down towards the swimmers. The swimmer without a goatskin looked to me to have an arrow (or two?) in them that would have come from that direction. Detail was hard for me to make out though.
(I'm purposefully arguing only pro diving, in case that's not clear.)
Given how it's nearly impossible to breathe under water without the air itself being pressurized, I highly doubt option one. If you ever tried breathing out of a tube underwater as a kid, you'll know exactly what I mean.
I've done this with a tube as a kid and get what your saying. But would a goat skin underwater be the same? The tube example is because of the pressure difference. Having a bladder underwater the air would easily come out to breath. IMO the harder thing would be getting the bladder to stay underwater, especially at the picture size, that would have a heap of buoyancy to offset.
The air in the bladder will be at exactly the same pressure as the water around it. Therefore if the diver were underwater with the bladder (a thing which I doubt, for reasons others have mentioned here), the air in the bladder would be at about the same pressure as the diver's lungs (about 0.2 psi higher, if the diver somehow managed to keep the bladder below him, as in the picture).
Additionally, a bag of air of that volume would not give much time underwater - maybe an extra breath or two. The extra effort and drag of carrying the bag would make it less effective than just 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!
Swimming was quite common in ancient Mediterranean area societies. They even did a lot of breath hold free diving, hunting for sponges and shellfish.
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.
When I was a kid we had an above ground pool that was about 3 feet/~1 m deep. One day in the shed I found a 6 foot/2m length of hose that looked to be about the same diameter as the tube on the my little snorkel. Ah ha! I can attach this to my snorkel, tie the other end to a pool float and breath under water like a diver!
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.
That was dangerous due to the risk of hypercapnia: "increased CO2 levels could lead to unconsciousness which, if happening while in the water, can result in drowning.". Note that our breathing is regulated by the amount of CO2 in our bloodstream, not the amount of oxygen. There is a fantastic explanation of the danger here: https://blog.daneurope.org/en_US/blog/are-full-face-snorkeli... There are safety regulations to limit the volume of air inside a snorkel (the dead space).
"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)
> 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...
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.
IIRC, the average air consumption is about 1 cu. ft./ min. at atmospheric pressure. Assuming the bladder is not pressurized, at a guess it could hold ~2 cu. ft., so maybe a couple minutes worth of air. If you could manage to submerge, that would be substantially longer than the average person can hold their breath, maybe enough to be worth it. (Notice the "if".)
It’s more complicated than that because the bag can be deflated unlike a scuba tank so you’re benefiting from normal atmospheric pressure. Assuming the scuba tank was filled with normal atmosphere and this bag was about the size of someone’s torso, it’s probably much closer than 200x.
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.
I used to be a scuba (SCUBA) diver, and yes, that is not so incorrect as you imply. See my post a little higher suggesting that the bladder could contain a couple cubic feet of air, which would give you a couple-three minutes.
The real problem is diving, rather than floating on top of (or more likely underneath) the bag, as others have pointed out.
Not regularly and only very shallow so my recall of the details isn’t great. But I do recall asking about even slower breathing and the response was it extracted more oxygen but wasn’t recommended due to the risks of disorientation. I think the 2x was in relation to failing to do slow deep breathing though.
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.
You're just so far off that I don't even know where to begin. Either the person you asked was completely confused, or you didn't understand what they told you. As a starting point I would recommend reading the US Navy diving manual.
Can confirm - I went on a bunch of dives with a former Navy Seal and he used less than half the air on any given dive than the rest of us (who were all only regular or advanced certified) did. His explanation was that he'd just mastered the meditative mindset/breathing technique to use as little air and energy underwater as possible.
Mindset and breathing technique is certainly important in minimizing open circuit gas consumption, but it's not the only factor. Some people just have a naturally higher tolerance for CO2 loading (the instinct to breathe is driven more by increase in CO2 levels rather than lack of O2). Perfect buoyancy control helps a lot since you're not wasting energy on depth keeping. Equipment configuration should be streamlined to minimize drag. A high level of physical fitness also allows you to keep your breathing under control during periods of exertion, like finning against a current.
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.
That’s true, but irrelevant in this case as in the short term people are O2 limited not CO2 limited which is why the world record for holding ones breath goes up by breathing pure oxygen.
It’s also one of the reasons I was asking for examples as I assumed you where making assumptions that didn’t apply.
For the vast majority of people that's just wrong. The urge to breathe is driven primarily by increasing blood CO2 levels (hypercapnia). You can learn to tolerate higher levels but to reach the point where pre-breathing pure O2 makes a difference takes extensive dedicated apnea training.
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.
> For the vast majority of people that’s just wrong.
>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.
Perhaps you could begin by explaining what's wrong, rather than citing a book (or actually not even a book, rather a page linking ten or so publications), with no indication of what part to read. I am of the opinion that you are the one who doesn't know what he's talking about.
> The volume would decrease rapidly with depth but the available oxygen per breath would increase to compensate.
> 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[*].
> 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[*].
-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...)
I am not saying it’s practical or their going to spend time at significant depth. The utility might have been a simple game of who could stay under water longer. That said, spending noticeably longer at 5-10m with an air filled bag weighted down by stones is a very long way from oxygen toxicity or the bends.
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.
Unless your short your estimate seems odd. The torso is about 1/2 the volume of the average adult and people are close to the density of water of 1kg/l or 2.2lb/l. So 30l would be the expected torso volume of someone weighing ~60kg or ~130 lb.
Edit: “47% trunk and neck” so 40% torso would be 75kg and 165lb seems reasonable as a smaller person would also need less air.
30L is 8 gallons. The average torso is somewhat longer than a five gallon bucket, but of course it's much slimmer than a five gallon bucket. An eight gallon bucket, if it existed, would be larger yet. I would question both the assumption that a torso is half the volume of a human and the further assumption that the density of humans is uniform. Obviously the thorax, which contains the lungs, is less dense than the legs, which just have muscles and massive bones with a thin layer of fat.
Sorry it took a while to respond; I got rate-limited this morning.
Agreed, also I think he's breathing into the bag not out of it. If you have a flotation device that's not fully sealed then you need to periodically re-inflate it a bit. It's the equivalent of keeping a leaky boat afloat by bailing water.
Yep. One of the first issues you'll encounter when learning to dive is getting your body to sink (that's what all those lead weights are for). I also don't think an inflatable goatskin has enough air capacity to be relevant.
One cubic foot of air displaces one cubic foot of water (compression notwithstanding). A cubic foot of water weighs 62lbs. I think you're vastly underestimating the bouyancy of an inflated bag. Try to pull a standard birthday party balloon underwater. It's nearly impossible to do. You would need a tremendous amount of extra weight to submerge a goatskin full of air.
I was referring to the bladder's capacity to store breathable air. I'm well aware how buoyant an inflated bag (or a wetsuit, for that matter) can be :)
Did you see the second image -- how about if it was deflated and used as a re-breather and was principally to stop exhaled bubbles from giving your position away to archers as you crossed a river/moat?
> 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.
Why have an inflatable goatskin that you're inhaling from for swimming on the surface? Considering the fish next to him it seems more likely the artist left out the boring aspects of holding rocks or whatever to reduce buoyancy.
Artists don't always use realistic perspectives, especially not that long ago. The swimmer isn't inhaling, he's blowing into the goatskin to keep it inflated. It's just like a modern inflatable life vest which has a manual inflation tube to use if the automatic inflator fails. There are no rocks (although ancient free divers sometimes did hold rocks to dive down faster).
No one has suggested one possibility: that this was the art work for an idea some Assyrian Beltway Bandit was trying to sell. 1000 units of Self-Contained Underwater Breathing Apparatus for the armies of Tiglath Pileser for the low price of 100 talents of silver. As seen on Rockovision!
I think you are right and the depicted soldiers are not diving but floating. Maybe they carried their weapon in the bag, they all seem unarmed. Also I was wondering why they would continuously have to blow air in the sack. Probably they weren’t airtight.
Not that heavy. Air displaces about 62 lbs of water per cubic foot, so a goatskin the size of your torso would require more weight than a soldier could carry to offset it.
Then you would just become buoyant and not even sink. Try to bring a basket ball to the bottom of a pool. Grab some bricks and a basket ball then see what happens.
No, it goes into your lungs and provides buoyancy for as long as you hold that breath. Some of the oxygen gets taken into your bloodstream, where it no longer provides buoyancy, but that's compensated by an (approximately) equal amount of CO2 that you exhale. But unless you blow it back in the bag, it ceases to provide you any buoyancy because it goes back into the atmosphere. (And if you do blow it back into the bag, your next breath will contain rather a lot of CO2...and the next one after that, even more.)
One thing I haven't seen mentioned which jumped out to me about the first theory is how would they have inflated the bag with breathable air in the first place? Were air pumps around back then?
I imagine you could have two bags, one big one, connected to a smaller one and squeeze air from the bigger into the smaller (many ways)... but sheepskin isn't going to hold a lot of pressure and would just bust (not sure but not as good as a soccer ball) and given it's "hotdog" shaped and not spherical, it's probably not more than 2 - 4 psi.
A related oddity - according to "Navies of the Napoleonic Era", Turkish ships had higher decks than was normal for other navies allegedly to allow for elaborate headgear, even though this actually compromised the stability of the ships.
If you're shooting, or dumping burning oil on your enemy, or even throwing rocks at them, being a bit higher than they are is a significant advantage, if for no other reason than the fact that you can see them better than they can see you. It's like the high ground in land battles.
This is in Napoleonic times, where naval warfare relied on broadsides of cannons. Stability is a far more important factor here. Also note that 4-decker ships, with a nominal advantage in firepower, were employed by the Spanish but eschewed by the Royal Navy for the same reason.
Is that a hold-over from Byzantium/Eastern-Roman-Empire, kept after the Turkish conquest? They were all about elaborate hierarchies of ranks and titles, often expressed through big hats or helmets.
Neat idea, but I'd bet it was a completely native decision, maybe forced on some poor naval architect by a grandee who didn't understand the implications of the order. Then again, there's no proof one way or another.
If it isn't symbolic, I'd guess the swimmer had just decided to abandon all but the most important piece of his kit. The helmet would also afford him a bit of safety if he stuck his head above water to see what's going on and where he is. Could also be a cuir-bouilli helmet/hat which I assume wouldn't restrict his swimming to the extent of bronze or iron.
Yeah, in general that wouldn't be surprising. The OP describes this guy as a "soldier", but I wonder if there's enough info to know whether he's just a soldier perhaps someone more important.
In this image the 'goatskin' users appear fully clothed in dresses (could they be scale armour or other weighted clothing), only one has a beard. A person without a goatskin appears "above" them (could be behind depending on perspective) and IMO appears to be getting shot with arrows. The "divers" aren't wearing onion-shaped helmets. The goatskins appear to be fixed to the belts on their waists.
One could interpret this as showing underwater swimming to avoid archers.
Perhaps it was an idea, rather than a practiced activity? Maybe the goatskin has rocks in it too, to balance buoyancy? Perhaps the carrying a rock bit was not shown for fear of letting enemies in on the idea!?!
[But yes, more probably a floatation device; fun to speculate though. Would particularly be interested to look at perspective in Assyrian bas reliefs]
Really interesting, would love to hear some Assyrian historians debate this.