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Okay, I'm only newly DIR, but I think I can answer your question.

...Or rather, elaborate on the other's correct answer of "DIR teaches a balanced rig."

The original question posed by faye was, "What's the DIR stance on redundant bladders?" (Forgive me for paraphrasing.)

The stance is, "No redundant bladders."

However, the question was later elaborated on, and again I'll paraphrase and say that the question was, "Well, how do they recommend I handle this situation?"

The situation, as best as I can tell from reading this thread, was this:

Salt water, open ocean dive
AL80 doubles rig
Backplate and harness
3 mm wetsuit
Properly weighted and trimmed for the dive

Here's how the situation would unfold, if the diver was diving the above rig:

The short version is that the diver would be properly balanced throughout the dive and buoyancy would never be an issue, even with a complete bladder failure.

The long version works like this (and you don't have to be a chemical engineer to understand this):

Let's assign some numbers to your rig so as to illustrate the way this would happen. These are common numbers that I personally have experienced:

Me: Relatively neutral in salt water
3 mil wetsuit: 8 pounds buoyant in salt water at the surface, 70% of that lost at 100'
Backplate: 6 pounds negative
Tanks: 2.2 pounds negative (each) at the beginning of the dive, 4 pounds positive completely empty
Weight belt: 10 pounds on the belt

Okay, let's say that at the beginning of the dive, I jump in the water and immediately sink to the bottom, uncontrolled. I have a complete and catastrophic bladder failure (unlikely, since it was tested on the boat.) If the problem is that my valves are turned off, then I simply reach back and turn them on. (Taught in DIR-F.) Likely, I can do this before I hit 20 feet. Of course, this would never happen, since I've responsibly tested my gear before getting in the water. However, assuming that it did happen, then let's see how the weight would work out:

Me: Relatively neutral
3 mil wetsuit: At 100', my wetsuit is (30% of 8 pounds) 2.4 pounds positive
Backplate: 6 pounds negative
Tanks: Combined, 4.4 pounds negative
Weight belt: 10 pounds negative

That puts me at 18 pounds negative. I can actually swim this up, buy why? I'd drop my belt and surface 8 pounds negative, at 30 fpm. Interestingly, much of this would be offset with my lungs (never holding breath, but filling them with each breath). Deco would be a nonissue, since I would not need a deco stop. I'd have only been in the water a matter of seconds. We're also assuming that the bladder failure is COMPLETE, and that there is no assistance from the bladder whatsoever. This is highly unlikely. The errant sharp object or swordfish would make it leak a good bit, but it would still hold some air. Even the elbow suddenly coming off would not produce a catastrophic failure... You could simply hold some buoyancy with it by placing your body horizontally, which you should be anyway.

At the surface, in that instance, here's how that would turn out:

Me: Relatively neutral
3 mil wetsuit: 8 pounds positive
Backplate: 6 pounds negative
Tanks: Combined, 4.4 pounds negative
Weight belt: Gone

That puts me at just 2.4 pounds negative, easily swimmable. The difference would be the buoyancy change in the wetsuit. Of course, don't forget that I'd be just 2.4 pounds negative with two full tanks of air on my back. I'm in no danger of drowning. And again, we're assuming that you don't have even one pound of help from the wing.

Of course, this scenario would never happen anyway, since:

1. I tested my gear before I got in the water.
2. I entered the water with a full air cell.
3. If the problem was valve-related, then I'd simply reach back and turn them on.
4. I also have the option of dumping air out of my tanks before surfacing... There is no emergency if I'm on the bottom with two full tanks. I could technically do this as a last resort instead of ditching my weights. (There's as much as 12 pounds ditchable there.)

However, the scenario that I think you're more apprehensive about is the scenario where there is a deco obligation. Here's how that would pan out at 100':

Me: Relatively neutral
3 mil wetsuit: 2.4 pounds positive
Backplate: 6 pounds negative
Tanks: Combined, around 5 pounds positive (remember, they're not totally empty yet)
Weight belt: 10 pounds negative

That places me at 8.6 pounds negative, and I'd swim that up. At 20 feet I plan to do a stop... But now I have this situation:

Me: Relatively neutral
3 mil wetsuit: 4.8 pounds positive
Backplate: 6 pounds negative
Tanks: Combined, around 6 pounds positive (they're getting empty)
Weight belt: 10 pounds negative

That places me at a little over 5 pounds negative, which is very managable, either with just lung power (the average lungs from full to empty can produce as much as 9 pounds of bouyancy) or with simple kicks (not as pretty, but just as effective). I have not bothered to ditch weights. And still, we're assuming NO help from any air cell at all, which again, is unlikely.

At the surface, here's how it would pan out:

Me: Relatively neutral
3 mil wetsuit: 8 pounds positive
Backplate: 6 pounds negative
Tanks: Combined, approaching 8.8 pounds positive
Weight belt: 10 pounds negative

That leaves me almost perfectly neutral... At least within a pound.

Thus, a redundant bladder is not necessary... And since a redundant bladder increases task loading with no benefit, DIR preaches that single bladders are a better choice. Additionally, a redundant bladder may actually give you a false sense of security, since as someone else mentioned, if you have a tear in one, you're likely to have torn the other as well. Two bladders does not mean that one will always work. In fact, in the specific examples that you stated, such as dangerous marine life or an errant sharp object, a redundant bladder would have failed just as easily as a single bladder.

Things get even simpler when using single tanks, since there is about a 6 pound swing instead of a 12 pound swing from full to empty tanks, and so the diver will be diving with even less weight.

The same math above can be applied no matter what your circumstance.

My recommendation, if you want the real answers to your question, is to pose them at your DIR-F class. They do this stuff for a living, and are much better at it than me, and can help you to understand even more.
 
SeaJay once bubbled...
Okay, I'm only newly DIR, but I think I can answer your question.
DIR preaches that single bladders are a better choice.

Sorry guys, I couldn't resist the pulpit approach that seajay took in his write-up.
 
nradov once bubbled...

It would be greatly appreciated if those who do not understand DIR would please refrain from making false statements about it.

I understand DIR completely. I own all the literature and have read it from cover to back. Many of my methods follow the basic concepts of DIR, do I call them that, of course not. I also keep in touch with people who have been diving the so called DIR method before GUE was created and before any book was writen on the subject and before someone put a silly name to it. As far as a balanced rig goes this rule has been around since the first tank was strapped on a humans back, this is nothing new, and the method of being able to swim to the surface or to what ever depth is also nothing new.



These arguments are great for controlled situations but I think the scenario’s are a little off. There are still allot of places in the world were helium is not available and your selection of tanks is not up too you. Some may say well, I just won’t go there and I applaud you for thinking that way. To say that a dual bladder is inapporpate in every situation is closing your mind. Once it's closed and you stop questioning you become a drone.
 
cnidae once bubbled...

To say that a dual bladder is inapporpate in every situation is closing your mind. Once it's closed and you stop questioning you become a drone.

GUE encourages questioning. You should try taking the class. You'd be amazed. When it comes to their methods of teaching, that's exactly what they ENCOURAGE... Questioning.

It's statements like this that show that you have no clue what you're talking about.

In and of itself, that's no problem... DIR doesn't care if you are clueless or not... It doesn't care what your personal, uneducated opinion is. If you want to dive with Hefty bags and cinder blocks, go ahead... DIR doesn't care.

The problem comes in when someone like you who proclaims to "understand DIR completely" goes and spouts this sort of pointless drivel. Then the incorrect message (that DIR is closed minded) gets spread, and suddenly there's a whole movement that's anti-DIR for no reason other than because some uneducated fool spread some wrong information based on some silly notion that they "understood DIR completely."

Let me tell you, bud... I also read the DIR stuff, and I've taken the classes... And I've practiced hundreds of times. *I* don't "understand DIR completely." How could you?

...And to me, your statement rings of the most closed-mindedness that I've seen in a long time. For you to call DIR "closed minded" is nothing but a farce.
 
SeaJay, Did I say GUE is closed minded? NO! Did I say all divers using the DIR method are closed minded? NO! I dive with GUE instructors often enough to know that they are very open minded at least the one's I know. It's a shame that some bad apples like Irvine has given the DIR thing such a bad rap and all the others that promote a negative attitude. What my comments were refering to is the people that close there mind, get a clue buddy and go read my post again I did'nt bash DIR or GUE.
 
I don't think this is nessesarily a dir question. I asked the DIR guys what thier stance was on redundent bladders because they have the most experience in that sort of thing, from my guesstamation. Just because you are not DIR dosn't mean you are this great open minded diver willing to try all kinds of new things. The majority of divers I know are NON-DIR and are the most pig headed divers you could ever meet. I think DIR gets picked on because it is a large group speaking as one voice. I've dove with only a couple GUE divers and they don't have small upper lip mustaches or have an out stretched are.

Let me tell you, bud... I also read the DIR stuff, and I've taken the classes... And I've practiced hundreds of times. *I* don't "understand DIR completely." How could you?

I would hope you would try to understand diving not DIR.
DIR is an opinion. If DIR helps you understand diving then bully for you, but DIR isn't diving, it is and approach to diving. Can easily be mixed up.
 
Sorry netdoc
didn't mean to get so DIR vs the worldish
Now back to the whole balanced rig conversation.


functions near their expansion point.

This is key to understand befor one understands boyancy:D

functions near there whata????:wink:
 
faye once bubbled...

I would hope you would try to understand diving not DIR.
DIR is an opinion. If DIR helps you understand diving then bully for you, but DIR isn't diving, it is and approach to diving. Can easily be mixed up.

Fair enough.

I didn't mix anything up, though... I was simply commenting on the fact that you said that you "understood DIR completely."

BTW, Irvine is not affiliated with GUE.

What GUE instructors did you dive with?
 
SeaJay once bubbled...



The problem comes in when someone like you who proclaims to "understand DIR completely" goes and spouts this sort of pointless drivel. Then the incorrect message (that DIR is closed minded) gets spread, and suddenly there's a whole movement that's anti-DIR for no reason other than because some uneducated fool spread some wrong information based on some silly notion that they "understood DIR completely."

Another problem is when divers with little actual experience preach what they have heard but not done.
Let me tell you, bud... I also read the DIR stuff, and I've taken the classes... And I've practiced hundreds of times. *I* don't "understand DIR completely." How could you?

How many classes? You've gotten in alot of practice in the last few weeks huh?

This is the tech section right? Have you ever attempted to manage a set of 104's and dry suit without your wing? Comming out of a cave? While doing some deco?

BTW in regard to your al tank buoyancy calculations...my al tanks are closer to 4 pounds neg when full and 2 pound pos empty. you also left out regs, manifold, bands, can light and all the other gear often used on a technical dive. And no we don't ditch the can light in a cave.

Putting together a balanced recreational rig is trivial. Tech rigs usually end up very heavy with full tanks.

Don't think of swimming up think of swimming out or holding position for decompression.

I've done it for practice and my wife has done it for real. I'm not using a second wing but...

Try it. Strap on a set of doubles, let all the air out of your wing and then go practice your DIR skills with nearly full tanks. Let us know how it works.
 
https://www.shearwater.com/products/teric/
http://cavediveflorida.com/Rum_House.htm

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