Assyrian soldier diving with an inflatable goatskin bag (ca. 865

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

#81

Post by mcswell » Tue, Sep 21, 2021, 2:14 AM UTC

trutannus wrote: post #76

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…

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.

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).

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

#82

Post by mcswell » Tue, Sep 21, 2021, 2:18 AM UTC

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…

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".)

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

#83

Post by mcswell » Tue, Sep 21, 2021, 2:21 AM UTC

nradov wrote: post #15

Retric wrote: post #13

Earlier quoted context omitted.

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 volu…

None of that is even close to correct. Are you a scuba diver?

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.

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

#84

Post by mcswell » Tue, Sep 21, 2021, 2:25 AM UTC

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-...

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.

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

#85

Post by mcswell » Tue, Sep 21, 2021, 2:32 AM UTC

djrogers wrote: post #51

simonh wrote: post #49

Earlier quoted context omitted.

As soon as you breathed in the air from the skin, you would lose the buoyancy form it and sink to the bottom.

Umm, what do you think happens to the air in that skin when you breathe it? It goes into your body, and continues to provide buoyancy.

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.)

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

#86

Post by mcswell » Tue, Sep 21, 2021, 2:34 AM UTC

tragomaskhalos wrote: post #25

abeppu wrote: post #18

I think it's interesting that he's shown swimming mostly nude but wearing a protruding hat which seems pretty impractical. Is the hat symbolic?

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.

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

#87

Post by mcswell » Tue, Sep 21, 2021, 2:41 AM UTC

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!

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

#88

Post by pbhjpbhj » Tue, Sep 21, 2021, 7:36 AM UTC

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.

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.

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

#89

Post by pbhjpbhj » Tue, Sep 21, 2021, 7:46 AM UTC

freeflight wrote: post #70

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…

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.)

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

#90

Post by tragomaskhalos » Tue, Sep 21, 2021, 11:01 AM UTC

mcswell wrote: post #86

tragomaskhalos wrote: post #25

Earlier quoted context omitted.

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.