Question about “balanced rigs” and having all ballast unditchable

[CT-Rich]

No need to suck down to zero. If you have a burst tank o ring and the tank fills with water as you swim to the surface, you can fill your SMB to establish positive buoyancy, but if that fails then dump the rig.

When has a burst o-ring ever resulted in a tank filling with water? What are you making them with? Detonator cord?

 

[Eric Sedletzky]

If you are in this situation, purge the air from 200 bar to 10 bar. An aluminum cylinder can be made to be positively buoyant. But if you are still too negative because of non-ditchable weights, inflate your SMB. If need be, dump the rig.

Why not just have a little ditchable weight that you can drop? End of problem.

 

[CT-Rich]

Why not just have a little ditchable weight that you can drop? End of problem.

That is such an AOW solution... soooo last century.

 

[lowviz]

No need to suck down to zero. If you have a burst tank o ring and the tank fills with water ...//...

Here is the difference between theory and practice.

I'm a born and bred solo diver and don't believe in much of anything other than physics and fatality reports. You make a small but deadly assumption. there is always air, not water, in your tank. Thus it has intrinsic buoyancy. Can you count on that to be forever true?

Water weighs a pint a pound. Your reg will most likely allow for backflow. Do the math, how much more do you 'weigh' if your tank becomes full of water. Or is that an impossible scenario that you don't need to consider?

 

[ScottFL78]

My answer is that it is a Doing it Right (DIR) term. "Balanced Rig" is a term that was probably coined by George Irvine. It has been continued by GUE as the President Jarrod Jablonski was also on the WKPP exploration with George. Equipment Configuration | Global Underwater Explorers

If you watch the video below it is still pretty relevent today (unless you despise DIR). In the video keep in mind that dive computers were closer to their infancy and weren't yet trusted but the rest is still relevant in my opinion.

 

[CWK]

When has a burst o-ring ever resulted in a tank filling with water? What are you making them with? Detonator cord?

Look at the video of a first stage o ring failure. The diver shut down the tank when switching to his pony at 1:51. I believe the reason for shutting down is to prevent water displacing air in the tank thereby making the tank quite negatively bouyant. You are at liberty to believe that a tank will not fill with water if the tank O ring, tank overpressure disc, or regulator first stage o ring fail.

 

[Eric Sedletzky]

Somehow I knew tech would leak into this thread. Aha! I knew it! You rascals, this isn’t a cave or a wreck and we don’t have deco obligations. Ditchable weight is NOT a “failure point”.
Even though, like boulderjohn said, this is the basic forum and regular single tank recreational diving was the original topic.

All right, this is the basic scuba forum, so let's try to deal with single tank, NDL diving for a little while. When PADI revised its standards a few years ago, part of the impetus was a study of dive fatalities. One of the things they found was that some single tank divers had successfully reached the surface in an OOA situation, been unable to fill their BCDs because of the OOA situation, been unable to stay on the surface, sank, and drowned. As a result, they put a greater emphasis on manual inflation of the BCD, and they added dropping weights on the surface.

But let's look at the situation a little further.

A weight check is typically done by dumping all air from the BCD while holding a normal breath. If you are properly weighted, you should float at eye level when you are not kicking. This is usually done with a full tank. Some people say to add enough weight to compensate for the loss of the weight of the air during the dive, but others say it is not necessary because of trapped air at the beginning of the dive. At any rate, the key idea is this: a properly weighted diver with an empty tank should float at least at eye level while making no effort whatsoever to stay afloat. A properly weighted diver with an empty tank should have a very hard time submerging. That diver should have no trouble staying afloat with an empty BCD and minimal kicking. A single tank diver who cannot stay at the surface with an empty tank is significantly overweighted.

Perfect!
How much more basic and simple can it get?
Newbies please read and make note of in case some genius is telling you that ditchable weight has gone the way of the dodo bird...not!

 

[CWK]

You make a small but deadly assumption. there is always air, not water, in your tank. Thus it has intrinsic buoyancy. Can you count on that to be forever true?

Water weighs a pint a pound. Your reg will most likely allow for backflow. Do the math, how much more do you 'weigh' if your tank becomes full of water. Or is that an impossible scenario that you don't need to consider?

I actually don't make the assumption that there will always be air in my tank. That is why I practice valve shut down when I practice switching to my pony.

Perhaps can convince @CT-Rich that a tank can fill with water.

 

[CWK]

Somehow I knew tech would leak into this thread. Aha! I knew it! You rascals, this isn’t a cave or a wreck and we don’t have deco obligations. Ditchable weight is NOT a “failure point”.
Even though, like boulderjohn said, this is the basic forum and regular single tank recreational diving was the original topic.

Perfect!
How much more basic and simple can it get?
Newbies please read and make note of in case some genius is telling you that ditchable weight has gone the way of the dodo bird...not!

I actually started diving without ditchable weights before I became a tech diver. There are recreational BCDs with trim weight pockets that can be used to replace weight belts. The Scubapro Hydros is such a BCD. In terms of recreational diving, better trim leads me away from weight belts.

 

[lowviz]

Jesus, Eric. See above. Give up.