[David]

I already know how this is going to end but I ask anyway.

if a 3 liter bottle with open end has x lift at ten meters how much lift does it have at 70 meters. yes I know it will take more gas because of the presure but the volume 3 liters will remain the same. As the bottle rises to the surface the gas will expand and escape from open end but will it still have same lift at depth.

David

 

[Ivon]

It will have a lift of X.

Hope that helps.

 

[David]

It will have a lift of X.

Hope that helps.

I agree with you but spent a good half hour trying to prove the point but kept getting told I was wrong.

er Garf? Glock? want to add your views

David

 

[nigelH]

if a 3 liter bottle with open end has x lift at ten meters how much lift does it have at 70 meters. yes I know it will take more gas because of the presure but the volume 3 liters will remain the same. As the bottle rises to the surface the gas will expand and escape from open end but will it still have same lift at depth.

Well at 10m it will have 6L (surface) of air in it (weight 7.8gms) and at 50m 24L (weight 31.2gms) so there is a loss in lift of 23.4 gms.

But that's less than 1%, about the same as three £1 coins.

 

[Garf]

david . use all the physics you want but I'm telling you if you take a massive lungful of air at 3 metres you are on the surface. do the same thing at 50m and you hardly move. surely its as simple as the weight of water above you

 

[Mal Bridgeman]

If the problem is as Garf has described, then the issue is not about the air in your lungs on its own. If you breathe in at 3m then of course there will be a slight buoyancy shift but it will also trigger expansion of gas in the suit and wing which will trigger even more expansion and then you are on the surface.

At depth a slight rise in depth caused by breathing in will have virtually no effect on the other gas.

Pedant Nigel, does you calculation allow for any compression of the sea water at depth and does that makes any difference to the buoyancy as being the weight of fluid displaced?


Mal

 

[Kalahari Diver]

Or you just move a small amount which near the surface with large relative pressure changes pops you up?

David.

 

[David]

david . use all the physics you want but I'm telling you if you take a massive lungful of air at 3 metres you are on the surface. do the same thing at 50m and you hardly move. surely its as simple as the weight of water above you

As I said mate your wrong

David

 

[David]

If the problem is as Garf has described, then the issue is not about the air in your lungs on its own. If you breathe in at 3m then of course there will be a slight buoyancy shift but it will also trigger expansion of gas in the suit and wing which will trigger even more expansion and then you are on the surface.

At depth a slight rise in depth caused by breathing in will have virtually no effect on the other gas.



Mal

Thanks Mal that clears it up nicely for me. as you say its not the gas in your lungs its the other air spaces not expanding at depth.

I just wish Garf was a better diver sometimes

David

 

[David]

Well at 10m it will have 6L (surface) of air in it (weight 7.8gms) and at 50m 24L (weight 31.2gms) so there is a loss in lift of 23.4 gms.

But that's less than 1%, about the same as three £1 coins.

I wish I could work that out. Thanks Nigel

edit you did do that based on H at depth and 100% on surface dint you

David

 

[BJ]

Shouldn't you people be out diving?

 

[Nick Kay]

Depends on whethe you're using a YBOD???

It will have a lift of X.

Hope that helps.

If you're wearing a YBOD then:
1. It'll have more lift cos YBOD users says they're always better
2. In which case X > X
3. Esp. if you're a Hull based YBOD user :teeth:

Hows things Ivon - let me know what you've got planned for this year

 

[Ivon]

If you're wearing a YBOD then:
1. It'll have more lift cos YBOD users says they're always better
2. In which case X > X
3. Esp. if you're a Hull based YBOD user :teeth:

Hows things Ivon - let me know what you've got planned for this year

Mal, you can't compress water, so it doesn't matter how much water is on top of the water around you.

Nick, were off up to Redcar this weekend. Still trying to sort an engine for the boat so are restricted to using others at the moment.

As soon as it's fixed and it's tested I'll give you a shout, as long as your Sub doesn't make our YBOD's go a funny colour

We have some excellent marks for this year.

 

[nigelH]

david . use all the physics you want but I'm telling you if you take a massive lungful of air at 3 metres you are on the surface. do the same thing at 50m and you hardly move. surely its as simple as the weight of water above you

That is complete garbage and contradicts both physics and the experience of every diver here.

I don't find any difference between the way I breathe to bounce over something in the water in the pool or at 50m. The only difference is how much it changes as I rise as there is a significant expansion going from 3 to 2 meters but none from 50 to 49.

Mal: I ignored water as the effect is less than the errors on my air numbers. I think you have to go over 2 kilometres deep to compress water 1%.

 

[Nick Kay]

Nick, were off up to Redcar this weekend. Still trying to sort an engine for the boat so are restricted to using others at the moment.

Scunthorpe club has just bought a 2nd RHIB - not seen it yet (I think we're going to base it at Whitby or similar), but it should be available & I've just bought a small 4x4 with a tow-bar :thumbsup:

As soon as it's fixed and it's tested I'll give you a shout, as long as your Sub doesn't make our YBOD's go a funny colour

You mean Green?

We have some excellent marks for this year.

Keep me informed - off to the Red Sea with SWMBO on Sunday, then teaching a few Nitrox courses & then should be in the salty stuff (though haven't got my CCR/Tx ticket yet :frown: )

 

[Ivon]

Scunthorpe club has just bought a 2nd RHIB - not seen it yet (I think we're going to base it at Whitby or similar), but it should be available & I've just bought a small 4x4 with a tow-bar :thumbsup:


You mean Green?



Keep me informed - off to the Red Sea with SWMBO on Sunday, then teaching a few Nitrox courses & then should be in the salty stuff (though haven't got my CCR/Tx ticket yet :frown: )

We have plenty of stuff in the 40m range and off shore so no need for mix, what are you qualified to on the unit? Give us a shout if you have any spaces out of Whitby, we will be taking ours up there and leaving it there for a few weekends at a time this season, if all goes well we will be leaving it up there next season.

 

[Nick Kay]

Ccr

We have plenty of stuff in the 40m range and off shore so no need for mix, what are you qualified to on the unit? Give us a shout if you have any spaces out of Whitby, we will be taking ours up there and leaving it there for a few weekends at a time this season, if all goes well we will be leaving it up there next season.

Cert'd to 45m on air dil. I'll need some shakedown dives in the sea in the 30-35m range before I go 35+ on the unit

 

[zepp]

I already know how this is going to end but I ask anyway.

if a 3 liter bottle with open end has x lift at ten meters how much lift does it have at 70 meters. yes I know it will take more gas because of the presure but the volume 3 liters will remain the same. As the bottle rises to the surface the gas will expand and escape from open end but will it still have same lift at depth.

David

yep..same amount of lift (1 ltr air volume, 1kg lift in fresh water) but like Nigel said there is a very slight loss due to the actual weight of the gas but its fairly neglegiable.

 

[Zarn Smith]

But if the cap is off the bottle, how can the gas be included in the weight calculations?

 

[zepp]

But if the cap is off the bottle, how can the gas be included in the weight calculations?

Each litre of gas has a weight at atmospheric pressure so at 50 mtrs you have 6 times the gas molecules within the same volume therfore 6 times the weight.