bc leak

[stuartr]

Originally Posted by GLOC

Nope you correct, you would be more 'overweighted' at depth, one of the reasons for taking redundant bouyancy on deep wetsuit dives.

I wonder how much the increased density of the air in you lungs effects bouyancy too. I reckon if deep enough even a fully functional bc would struggle to lift due to the increased density of the air in it. I don't know at what depth that could start to kick in though..

I never really thought of a DSMB as being a redundant bouyancy device. Which I guess is the point of this thread.
Another good reason for carrying one.
Though I shall be more thorough in checking my bc in future also. A good idea would be to put air in the bc and squeeze it with your arms and check for leaks perhaps...
Stuart

[GLOC]

I think you would have to be f**king deep to get that sort of issue occuring bearing in mind that guys in Wakulla are regularily down in the region of 100m with lots of stages and reels (scooters should be neutral).

Regards

[stuartr]

Originally Posted by GLOC

I think you would have to be f**king deep to get that sort of issue occuring bearing in mind that guys in Wakulla are regularily down in the region of 100m with lots of stages and reels (scooters should be neutral).

Regards

You're probably right, but there again they probably have enormous wings with loads of lift too.
Actually thinking of the Physics.......
The upthrust is equal to the density of the fluid displaced so therefore wouldn't change, but the density of the air would increase say 7 times at 60m which if you had say 20 litres would be equivalent to an extra 0.18 kg (1.29x7x0.02), less actually as the air is not behaving as an ideal gas...
So I guess I'm talking cr@p
I agree if you were deep enough for it to make a major difference you would probably not be in a state for it to matter anymore.

[Smiling Dragon]

Some assumptions:
A BC gives 18kg of lift on average (ref)
1 cubic foot of air displaces 29kg of water
-> Avg BC holds about 0.62 cubic feet of air

Air density doubles approx every 10 meters

A cubic foot of air weighs around 37.65 grams on the surface

-> For a BC to stop working, the air inside it would have to weigh 18kg or more when full
On the surface, that would be around 478 cubic feet of air

-> My maths says that at around 95 meters your 18kg BC would not generate any lift even when full.

Does that sound right?

[GLOC]

However you would have other issues because at 95m you are likely to be carrying far more cylinders than a single BC could cope with on the surface and so you would use something like a 55 or 60lb wing.

[Fiona]

Some people really should have better things to do than post in forums

[recurve]

Originally Posted by Smiling Dragon

Air density doubles approx every 10 meters


Does that sound right?

No it doesn't, the increase in air density is linear not exponential. It only doubles in density over the first 10 meters, thereafter the increases in density become smaller.

[stuartr]

Originally Posted by recurve

No it doesn't, the increase in air density is linear not exponential. It only doubles in density over the first 10 meters, thereafter the increases in density become smaller.

Physics geeks of the world unite.

Agreed.... at 20m it would be at 3 atmospheres and at 1/3rd its volume, at 30m 1/4 this is linear (density proportional to Pressure )up to when it starts to get so compressed it stops behaving like an "ideal gas."

[stuartr]

Originally Posted by Smiling Dragon

Some assumptions:
A BC gives 18kg of lift on average (ref)
1 cubic foot of air displaces 29kg of water
-> Avg BC holds about 0.62 cubic feet of air

Air density doubles approx every 10 meters

A cubic foot of air weighs around 37.65 grams on the surface

-> For a BC to stop working, the air inside it would have to weigh 18kg or more when full
On the surface, that would be around 478 cubic feet of air

-> My maths says that at around 95 meters your 18kg BC would not generate any lift even when full.

Does that sound right?

Eugh! Kg and cubic feet, messy units.
To compress 478 cubic feet into 0.62 cubic feet you would have to be at 771 atmospheres.. about 7.7km deep....Now you are definitely in the sh1t if diving a single 12litre and you should consider a shallower wreck for your second dive.

[stuartr]

Originally Posted by Fiona

Some people really should have better things to do than post in forums

harsh but fair.