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Assyrian soldier diving with an inflatable goatskin bag (ca. 865–860 BC)

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Re: Assyrian soldier diving with an inflatable goatskin bag (ca. 865–860 BC)

#61

Post by sbacic »

caymanjim wrote: post #47
sbacic wrote: post #5

Earlier quoted context omitted.

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 :)

Re: Assyrian soldier diving with an inflatable goatskin bag (ca. 865–860 BC)

#62

Post by eric_h »

nradov wrote: post #27
Retric wrote: post #17

Earlier quoted context omitted.

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 b…

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. https://www.navsea.navy.mil/Home/SUPSALV/00C3-Diving/Diving-...

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.

Re: Assyrian soldier diving with an inflatable goatskin bag (ca. 865–860 BC)

#63

Post by nradov »

eric_h wrote: post #62
nradov wrote: post #27

Earlier quoted context omitted.

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. https://www.navsea.navy.mil/Home/SUPSALV/00C3-Diving/Diving-...

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.

Re: Assyrian soldier diving with an inflatable goatskin bag (ca. 865–860 BC)

#64

Post by mod »

caymanjim wrote: post #45
killjoywashere wrote: post #36

Earlier quoted context omitted.

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.

Re: Assyrian soldier diving with an inflatable goatskin bag (ca. 865–860 BC)

#65

Post by MisterTea »

LeifCarrotson wrote: post #6
nradov wrote: post #2

He's swimming on the surface. That bag would be too buoyant for diving.

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 abo…

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.

Re: Assyrian soldier diving with an inflatable goatskin bag (ca. 865–860 BC)

#67

Post by trhway »

killjoywashere wrote: post #36
pbhjpbhj wrote: post #16

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), o…

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.

>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.

Re: Assyrian soldier diving with an inflatable goatskin bag (ca. 865–860 BC)

#68

Post by Retric »

jessaustin wrote: post #60
Retric wrote: post #29

Earlier quoted context omitted.

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 le…

Ok in anatomy the torso is shoulders to anus. Various other places use shoulders to top of hip bones. https://en.wikipedia.org/wiki/Torso vs https://www.wikihow.com/Measure-Torso-Length

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...

Re: Assyrian soldier diving with an inflatable goatskin bag (ca. 865–860 BC)

#69

Post by Retric »

nradov wrote: post #63
eric_h wrote: post #62

Earlier quoted context omitted.

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…

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.

Re: Assyrian soldier diving with an inflatable goatskin bag (ca. 865–860 BC)

#70

Post by freeflight »

pbhjpbhj wrote: post #16

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), o…

> One could interpret this as showing underwater swimming to avoid archers.

Could also be the scene of a siege, the swimmers trying to traverse a river with heavy currents, indicated by the swirls in the water.

In that scenario the archers would give them covering fire from the defending soldiers in the castle structure.

This could also explain the archers wearing different helmets: They belong to different sides in the conflict.

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