Twinsets, redundancy, and what problem are we solving...

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

Don't care what you do, doubles, separate tank or tanks,,, it really comes down to the operator,
It's a poor diver that blames his tanks and equipment...
The diver is responsible to know the advantages and limitations to the gear,


One sidemount question I do have....
Has anybody ever experienced less air in one of the tanks that you are not using...
Like an low pressure air leak or current pushing the reg diaphragm and you not noticing?
That is something that I could see happening kinda accidentally....
 
1) First, you have twice as much equipment to monitor ... three is very little possibility that the cylinder will loose pressure during the dive.

2) Second, there is an issue with streamlining. I dive a high current river, and any extra equipment adds drag. In pristine environements without current, this probably is not much of a problem, but in a river, it can make quite a difference.

3a) Not if your are properly trained. 100 feet is 4 atmospheres absolute, meaning that the air density at 100 feet is 4 times denser than at the surface. That also means that upon a CESA, the air in one’s lungs expands to four times its original volume.

3b) I did this as an experiment in my local pool

3c) So not only is a CESA possible from 100 feet, Jacques Cousteau described it as an “enjoyable experience” for highly trained divers.

4) What we have now is divers who are not highly trained, have minimal water skills, and are not relaxed in the water. Agencies responded with equipment “redundancy” rather than training. Carry this tank and simply switch, rather than not carrying a spare tank and relying upon water skills. The equipment manufacturers and dive shops jumped on this, as they could sell more equipment, and make more money.

SeaRat
1) At this time, I put SPGs on every cylinder/reg, even if they have AI. Sometimes that's a button SPG. Maybe you don't technically need it, but it can be helpful for knowing you need to cut your safety-stop a little short.

2) I'm always a fan of streamlining.

3a) That makes sense. However, like you mentioned, as a lightly-experienced (about 200 dives?) scuba-diver, CESA at 100ft isn't something I would know how to practice safely, nor would be highly confident in my ability to perform. I would simply head for the surface, breathe out slowly, and hope I make it. There are some obvious safety limitations with actually doing a 100ft CESA, just for practice.

3b) Interesting exercise.

3c) Perhaps if I could safely practice it.

4) I definitely understand the general critique of the dive industry. I'd even say classes are setup in such a way as to instill learned dependency. I fully understand there can be unanticipated and unintuitive hazards of types of diving beyond one's training level, however one doesn't need a "wetsuit flattuance" certification to fart in a wetsuit. (I'm still skeptical about the whole solo-certification. Cary a pony bottle, be extra careful, and consider other forms of redundancy.... got it)

The difficulty of "get good" type advice, is we're still back to step-1, in terms of where or how does a diver learn these skills you talk about? We have the dive-agency-training issues mention, and others not mentioned, but that's ultimately where most people have to go for training these days. So, as a diver, I dump $250 to $1000 on some class, where only a little makes it into the dive-instructor's pocket. Meanwhile, (I've heard) some agencies apparently don't allow instructors to train anyone outside a formal class, and the formal classes of course follow a specific curriculum.

For the moment, I'm okay with being a "scrub" with a pony-bottle. It's rigged up nicely, hoses bungeed, etc. I feel safer with that, than the idea of air-sharing with a buddy-hazard. Though if I can practice a 60-100ft CESA safely, I won't complain about having a 3rd form of redundancy.
 
One sidemount question I do have....
Has anybody ever experienced less air in one of the tanks that you are not using...
Like an low pressure air leak or current pushing the reg diaphragm and you not noticing?
That is something that I could see happening kinda accidentally....
That seems unlikely, but not impossible. Before side-mount, I had a regulator come unscrewed. I noticed the problem and proceeded to surface immediately.


You can always pressurize a regulator, but then shut off the tank. This would prevent the regulator from flooding, while also prevent a free-flowing reg dumping your tank. The only downside, is you have to turn on your tank before you can use it. (You may get a breath, depending on depth) Turning on/off tanks is a skill practiced in some tech-classes, and is something you should be able to just practice even without a class.
 
helpful for knowing you need to cut your safety-stop a little short.
As this is an Advanced section and we are talking about Solo diving, when did any safety stop become mandatory? I can ALWAYS cut a safety stop short.
 
Unfortunately today's diver can't swim, they don't have the agility to move around underwater like the Causteau team. They can't swim to the bottom or more importantly swim to the surface. So there always looking for a gear solution which further limits the agility to move in the water. The surface was always the natural bailout when available but not anymore. There carrying so much gear they can't swim to the surface.
A perfect example of
“Less is more”.
The less you have on the more agile you are and the more ability you have to self rescue.
When I was diving a drysuit, long hose, a slung pony or small doubles (twin 72’s) I felt very constricted and choked. Not enjoyable at all. As soon as I ditched all that crap and went back to a basic wetsuit and a single tank with just basic gear doing fun basic dives I felt liberated. At one point I got into no BC diving and that was about as liberating as it gets. This is all in cold rough ocean water with surf and swells, currents, kelp, etc. where most people wouldn’t dare dive, at least most people around here.
 
Your planning is to have enough gas to safely finish the dive should Kaboom! happen.

Things to consider
  • an elevated breathing rate — it’s stressful!
  • any decompression obligation
  • depth - affects gas consumption rates
  • where is your first stop; is that a decompression gas or is it the surface
  • any additional time required for the peril; overhead, return to shot line
  • Contingency reserve
This gives you an idea of the additional time required, thus the additional gas required to get you out of there.

You then need that amount of gas in both cylinders such that if either Kaboom! fails, you’ve enough in the other side.

This could be two thirds, it may be more or less.
Does kaboom happen often?
Have you ever had kaboom happen to you? I never have.
Do you know anybody that kaboom happened to?
What causes kaboom?
What is kaboom anyway?
 
That seems unlikely, but not impossible. Before side-mount, I had a regulator come unscrewed. I noticed the problem and proceeded to surface immediately.


You can always pressurize a regulator, but then shut off the tank. This would prevent the regulator from flooding, while also prevent a free-flowing reg dumping your tank. The only downside, is you have to turn on your tank before you can use it. (You may get a breath, depending on depth) Turning on/off tanks is a skill practiced in some tech-classes, and is something you should be able to just practice even without a class.
Or, you could use a regulator that has a spring-loaded “dive/pre-dive” switch that you put into the pre-dive mode so it won’t free flow, ever. Scubapro made their Pilot/A.I.R. I regulator in this manner, and I have both. Some of their subsequent regulators also had this mode. Dacor made the PACER regulator, which had a built-in automatic design which would stop free-flow in about 4 seconds. It was a patented entryway for water to get into the second stage. Either of these two designs precluded free-flows as a hazard.
fullsizeoutput_1fc2 by John Ratliff, on Flickr
This is the Scubapro Pilot regulator, with the black slide a switch for the “Dive/Pre-dive” positions.


AIR I Performance001 by John Ratliff, on Flickr
Here is the instructions for the A.I.R. I regulator by Scubapro.

IMG_0081 by John Ratliff, on Flickr
This shows the insides of the second stage of the Dacor PACER regulator, which has a special vertical metal plate which allows water into the second stage so as to stop free-flows in about 4 seconds. It works! This plate is at the bottom, fitted into the mouthpiece tube on the far left. In addition, you’ll notice a vane on the demand lever. This vane, when pulled down into the Venturi stream, deflects the demand lever upward if an extreme Venturi occurs, pushing that lever out of the air stream and adding to the anti-free-flow action of this regulator.

SeaRat
 
As this is an Advanced section and we are talking about Solo diving, when did any safety stop become mandatory? I can ALWAYS cut a safety stop short.
We're in agreement, that a safety-stop is not mandatory. You seem to be "reading between the lines" and interpreting something I didn't intent to write.

My point was about the ability to know how much air remains in your redundant-air tank as you surface, so you can plan and respond appropriately. It's very common for people to burn through air at a SIGNIFICANTLY higher rate in emergencies, along with being unable to focus, gauge time, etc.

For example, not knowing how much air you have, trying to surface from 130ft, might cause one to surface faster than necessary and risk DCS to avoid drowning. Alternatively, if you run out of air prematurely on your spare, thinking you have 1000psi left, you might risk drowning as well.

Having a button-gauge or SPG on a short-hose seems like an easy solution.
 
Does kaboom happen often?
Have you ever had kaboom happen to you? I never have.
Do you know anybody that kaboom happened to?
What causes kaboom?
What is kaboom anyway?
Never happened to me either. Have had some hoses and connectors that leaked, but no "kaboom" hose or regulator failures.

But I'm glad to say that the coroner won't need to put "didn't have sufficient resilience nor skills whilst diving solo" on my death certificate.

However, I did do a full and complete bailout a few weeks ago. My rebreather completely failed (caustic cocktail) and I needed to do a decompression ascent on open circuit. Fortunately the practice skills all came in to play and I had more than enough gas for the short 35 minute decompression schedule.
 
I have had only one kaboom happen in over 60 years of diving due to a regulator, and that was about two years ago when I put a Sportsways Hydro-Twin with a Sportsways Sea-Vue SPG onto a 3000 psi twin 45 set. The SPG was not made for 3000 psi, and it exploded immediately upon pressurization. The SPG was also about 60 years old at the time.

I’ve had maybe one or two times where an O-ring on the tank/first stage blew, and again that was on pressurization.

These kind of “kaboom” moments have never happened to me underwater.

SeaRat
 

Back
Top Bottom