Ok, a serious question about balanced rigs

[Reg Braithwaite]

With havy doubles you end up not controlling nouyancy with the drysuit. YOu'd hve to add too much air. You end up managing bouyancy with both wing and suit, essentially putting enough ait in the suit to just avoid the squeeze.

Which raises the issues of the utility of this concept when diving dry. There are plenty of rigs out there you can't make bouyant with a drysuit. Twin steel 120s with two slung steel 40s (with all the stuff that goes with that) is not going to be swum up no matter you what do with the drysuit.

Ok, let me try to explain my understanding and please tell me if I am completely confused. It could be that my 30/30 Bolivian/Haitian mix hasn't kicked in yet this morning (That's coffee, folks, hold the jokes).

At the end of my dive, doing a 10' stop, I should be neutral with nearly empty tanks and no air in my wing or suit. Therefore, when I first enter the water and do a bubble check at 10', , I need enough air in my wing/suit to compensate for the weight of the air in all my (full) tanks. If my rig is balanced, that's all the lift I need.

So given a balanced rig, the question is whether a dry suit has enough lift to compensate for the weight of all that air. I would expect that much air to weigh 25 pounds, which is a lot of lift to expect from a dry suit.

If that was all that mattered, we would dive 30 pound wings. Which leads me to infer that a set of twin 120s and two slung 40s is not balanced, meaning that with all tanks empty you cannot hover at 10' with an empty wing and suit, but you must have some air in the wing at all times during the dive.

I started this thing wondering about fixed floatation. The question of stages/deco bottles complicates things, because it seems dangerous to me to assume you will not drop a bottle. So I think that the best you could do with fixed floatation doo-hickies would be to balance the back gas cylinders. I conjecture, you could arrange things such that the twin 120s are balanced, and if you hover at 10' with empty cylinders the only air needed would be to compensate for the weight of the slung 40s less their buoyancy.

 

[JeffG]

With havy doubles you end up not controlling nouyancy with the drysuit. YOu'd hve to add too much air. You end up managing bouyancy with both wing and suit, essentially putting enough ait in the suit to just avoid the squeeze.

Which raises the issues of the utility of this concept when diving dry. There are plenty of rigs out there you can't make bouyant with a drysuit. Twin steel 120s with two slung steel 40s (with all the stuff that goes with that) is not going to be swum up no matter you what do with the drysuit.

If you are diving air in those twin 120's with your dual steel 40 deco bottles, I would recommend a double bladder wing.

 

[spectrum]

All that being said, air is still compressible, so we still need to compensate for depth, no? Just a lot less than neoprene, correct?

Everything is variable and it's all relative. How's that for useful information?

Wetsuits will vary with thickness, quality and condition.

Drysuits will vary with material (neoprene/laminates) and garments. Some garments are fairly compression resistant on their own and will have more buoyancy without air injection than others. A wetsuit equilibrates to the pressure of depth essentially instantly. A drysuit will vary with valve performance, valve setting and the divers skill at presenting trapped air to the valve.

Some divers make up for a marginal garment with more air to force the loft. Other divers invest in garments that are less dependent on injected air.

It all comes down to being familiar with your gear and knowing how to fly it.

As to your original question about negating overly negative doubles with fixed displacement buoyancy the answer is sure but it will again be a holistic answer in the end.

First I would not rely on any sort of foam or soft structured material.Most foams would crush with pressure, loose buoyancy and not recover fully, in effect just moving or compounding the problem. Sealed metal cylinders or even PVC pipe would work for the pressures involved. A manually operated ballast valve could even be included for fine tuning by admitting water to reduce lift.

Hard cavity BCs have been attempted commercially in the past but so far have all been kludges. The trick is getting the ballast (water) out to increase buoyancy. If you dig around in the vintage forum or someplace like vintagedoublehose.com you can find examples. Do not confuse them with things like the Cousteau hydrodynamic shells which were cylinder fairings.

The idea of a rigid chamber BC device is intriguing. In the world of cold water diving in any sort of dive suit a fair amount of BC air is needed at times to manage the variables of cylinder contents and suit behavior at depth. These are inescapable. The third thing thanks to Boyle s law is that very air we add to the BC to manage buoyancy is also morphing in size as we change depth and pulling our buoyancy away from center. If BC lift was not depth dependent then the cold water diving experience would take on more of the 3 dimensional freedom enjoyed when diving in limited neoprene in warm water.

Pete

 

[Slonda828]

If you are diving air in those twin 120's with your dual steel 40 deco bottles, I would recommend a double bladder wing.

+1 for JeffG's comment. I personally feel that I should be able to swim any rig up from any depth I dive to without a BC for help. I realize that sometimes that is simply not achievable, especially with exceptionally heavy tanks or drysuits. In that case you really have two options if you have a serious failure. You can either wear an individual weighting system (as in non-weight integrated) and ditch gear to get yourself buoyant enough to swim up, which may include ditching your doubles and breathing off of a stage or pony if depth/mix/etc permits (which is complicated) or you can use a double bladder wing. Looking at these two options when placing ones self in the hypothetical situation of being task-loaded, I would definitely go with Jeff's option.

S

 

[JeffG]

+1 for JeffG's comment. I personally feel that I should be able to swim any rig up from any depth I dive to without a BC for help. I realize that sometimes that is simply not achievable, especially with exceptionally heavy tanks or drysuits. In that case you really have two options if you have a serious failure. You can either wear an individual weighting system (as in non-weight integrated) and ditch gear to get yourself buoyant enough to swim up, which may include ditching your doubles and breathing off of a stage or pony if depth/mix/etc permits (which is complicated) or you can use a double bladder wing. Looking at these two options when placing ones self in the hypothetical situation of being task-loaded, I would definitely go with Jeff's option.

S

Personally...I would ditch the air, steel deco bottles and the dual wing and just dive a balanced rig in the first place.

 

[Reg Braithwaite]

+1 for JeffG's comment.

It set my sarcasm detector off. But I don't know his internet persona very well, I may have mis-calibrated.

you really have two options if you have a serious failure. You can either wear an individual weighting system (as in non-weight integrated) and ditch gear to get yourself buoyant enough to swim up, which may include ditching your doubles and breathing off of a stage or pony if depth/mix/etc permits (which is complicated) or you can use a double bladder wing.

As others have noted, some choose to avoid some of these problems by using lighter stage/deco bottles and lighter gas mixes. But given a dive like this on air, do you not have the third option of using an appropriately configured and sized lift bag as a redundant source of buoyancy?

 

[Slonda828]

But given a dive like this on air, do you not have the third option of using an appropriately configured and sized lift bag as a redundant source of buoyancy?

Of course JeffG is sarcastic...he's JeffG. You gotta love him. First, let me caveat this by saying that in diving, you CAN do whatever you feel is right. I dive vintage gear with no octo, no BC, and a huge dive knife. I don't implode when I dive my old gear so I would first say do whatever you think is right. As far as what is right for me personally, I will not dive a rig I can't swim up. I never have, and I never will. If I have to use a lift bag (whose primary purpose in my mind is light salvage having been a military guy) to get up, then my stuff is too heavy. I am just of the opinion that you should be able to swim, and not depend on equipment to make you safe. Please understand that whatever works for you....works for you. Are you having trouble constructing a doubles rig that is balanced?

 

[Slonda828]

Obviously, if diving a heavy wet suit you'd need a ton of ditachable weight to overcome the buoyancy at the surface, I get that and will stick with my dry suit for warmth and redundancy.

Reg,

Another way to do this is to dive slightly light. I'm not talking light enough to pop up like a cork when your cylinder(s) is at 500psi, but slightly light. It's a lot easier to swim up a deflated rig when you are barely on the light side at the surface. I always dive 1-2 pounds light, and once I get down to my target depth my wetsuit crushes and I'm aces. This is just what works for me though, and I usually dive without a BC so we tend to weight ourselves a little differently. In fresh water, for example, I dive a 3mm wetsuit with 3 pounds of lead. Obviously with a heavy wetsuit like you mentioned it would require more lead, but it's not hard to sit at a safety stop if you are only 1-2 lbs light. That's pretty easy to control with your breathing. I understand that gas consumption would in reality make you 4-6 lbs light overall if you started with a full cylinder and hit your safety stop with 500psi or so, but it works for me. I have never once rocketed to the surface, and I don't have to kick to stay down.

 

[Reg Braithwaite]

Of course JeffG is sarcastic...he's JeffG. You gotta love him.

I enjoyed that comment and would have upmodded it if we were on a reddit- or digg- style forum.

Are you having trouble constructing a doubles rig that is balanced?

The original question was purely speculative. I had read some other threads arguing about redundant bladders and what-not, and wondered whether a fixed and fail-safe float could solve some of those issues, in a theoretical, shooting the breeze, day-dreaming kind of way.

 

[JeffG]

The original question was purely speculative. I had read some other threads arguing about redundant bladders and what-not, and wondered whether a fixed and fail-safe float could solve some of those issues, in a theoretical, shooting the breeze, day-dreaming kind of way.

Some sets of doubles lend themselves to being "balanced" easily. Others not so much.

Double Al 80's balance quite nicely. Double 130's in fresh water (with nitrox) are almost impossible.

Addition equipment will either make the system worse or better.

You only have to answer to yourself, so do whatever floats your boat...everything else just provides amusement on the internet.