Dual-bladder or single-bladder? The whys and wherefores...

[Graeme Fraser]

(Disclaimer: I'm posting in the Advanced forum instead of the Technical forum because the question I'm asking applies to solo divers as well as tec divers. Mods, please feel free to move if necessary.)

Here's the scenario: I dive SM, often solo, and I live just outside Atlanta, where the summers are legendarily hot and humid. Thus, drysuits are not really a tenable option year-round, and in the summertime, I often dive wet, even when the bottom temps are about 50F/10C. For all this SM diving, I commonly use a double-bladder Hollis 100 with the Edd mods.

I'm also taking a Tec40 class and looking to continue down the tec path, meaning (a) I need redundant buoyancy, and (b) I'll also need to carry more tanks with special blends. It's certainly possible to sling multiple tanks SM, but diving a BM twinset in a tec scenario would make efficient use of unused space and have the extra benefit of reducing underarm clutter.

Thus, I'm vaguely considering buying a bp/w setup so I can do BM doubles, but @tbone1004 pointed out in another thread that there's some controversy about whether double-bladder wings are good ideas.

So let's talk about it. What are the up- and downsides of double bladders?

Oh...and before you post, please note that "OMG it's gonna kill you" or any other similarly hyperbolic post will be summarily ignored. Let's keep it calm and logical. (Yeah, I know...this is ScubaBoard...but I'm still asking.)

As you mention that compliance with PADI standards is a consideration for your upcoming Tec40, I would suggest talking to your preferred instructor to make sure you're both on the same page. For info, PADI recently amended their instructor manual with revised guidance on redundant buoyancy (see below).

 

[Diving Dubai]

The problem then is that it potentially takes longer to connect the power inflator to the secondary wing (or to inflate the wing orally) than it would to deploy a lift bag from a pocket or other reasonably accessible location. The usual approach is to inflate orally, but when a good deal of the wing capacity is in fact needed, this takes time and concentration. Once a lift bag starts to fill from a regulator that has the purge button depressed, it fills quickly.

I’m sorry, but not only do I disagree with this, I consider it to be nonsense.

It takes no time at all to connect a second inflator, compared with un clipping a lift bag, then filling etc

I dive a dual bladder SM rig, with one inflator disconnected

Inflator connect/disconnect is an OW skill

 

[Centrals]

I have been diving with twin bladders since 1998/9. The redundant wing had bailed me out quickly on two occasions. Even if I had not used the redundant wing during a normal dive, it still got the same treatment as my primary wing ie. wash, rinse, dried and slightly inflated in storage.
The secondary inflator hose is NOT attached to the power inflator but within easy reach if I require it.

 

[2airishuman]

I’m sorry, but not only do I disagree with this, I consider it to be nonsense.

It takes no time at all to connect a second inflator, compared with un clipping a lift bag, then filling etc

I dive a dual bladder SM rig, with one inflator disconnected

As I recall, you dive where it's always warm.

Connecting an inflator hose is no small thing in thick gloves suitable for cold water.

Inflator connect/disconnect is an OW skill

Disconnecting an inflator, located in the usual position on the left side of the chest, is an OW skill. Most people can do it quickly. Most people are right-handed and can use their dominant hand. Most OWDs can connect an inflator in-water after a certain amount of fumbling around.

Connecting an inflator quickly in a developing emergency, with gloves on, is not an OW skill. With a backup wing or bladder, the inflator is on the right side of the chest. Most people will find it more awkward to do than on the left side.

 

[Diving Dubai]

Connecting an inflator quickly in a developing emergency, with gloves on, is not an OW skill. With a backup wing or bladder, the inflator is on the right side of the chest. Most people will find it more awkward to do than on the left side.

So what are you saying? In the same situation, getting a liftbag out from stowage, clipping it on, inflating it with an octo and maintaining a safe buoyant ascent - is easier and safer?

Excuse my incredulity. When the majority of divers struggle with DSMB deployment, shallow without any other task loading

Whatever redundant buoyancy method is chosen, it is up to the individual to become proficient. If a diver can't manage a simple task like connecting an inflator that's on the RH side, then really they shouldn't be getting into Tech.

Heaven help them if they need to clip and unclip cylinders etc

Wearing of thick gloves shouldn't make any of these tasks more cumbersome then the basic skills that need similar dexterity and motor skills

 

[Centrals]

Orally inflate the secondary wing is much quicker.

 

[TrimixToo]

If you dont ever use the second bladder it may become unusable on its own from the pressure of the other bladder. Especially true if once used and than not for a long time the bladder inside sticks to itself making it unusable. Using 2 needs 2 hoses and is another FAILURE POINT as many look at it. I recently had someone ask the same thing thinking if he had a dual 40# bladder he could if needed get 80 lift from it. nO NO NO . His next thought was to alternate usage of them. did n ot appear to be a good stratagy either. then it was he could getting a small dual bladder and use the second only when on the surface to reduce the moving bubble. He finally gave up on the idea, especially when he was thinking about having second airs on both. As redicuous as it sounds I kinds wish that we had the old horse collars as a backup

Putting it on more or less at random (which side is "front" on a dual bladder wing, anyway?) solves the first problem neatly. It moves my signalling whistle from one side to the other but that's about it.

I have never attached hoses to both sides of a dual bladder wing at the same time. It's easy enough to move the LP hose or inflate orally (the way I learned to dive, way back when), and if I have a runaway inflator I don't want to have to guess which side is running away and possibly spend time detaching the wrong side first.

 

[NAM001]

Putting it on more or less at random (which side is "front" on a dual bladder wing, anyway?) solves the first problem neatly. It moves my signalling whistle from one side to the other but that's about it.

I have never attached hoses to both sides of a dual bladder wing at the same time. It's easy enough to move the LP hose or inflate orally (the way I learned to dive, way back when), and if I have a runaway inflator I don't want to have to guess which side is running away and possibly spend time detaching the wrong side first.

there are certainly pros and cons to them. my only experience is one of observatoin. a dual bladder came into a shop both bladders had been used. one of them suposedly only once. the other was the primary bladder. It is guessed that from no use the unused bladder with moisture in it and being compressed by the primary bladder when stored caused the insides to bond, and when inflated tore. No one knows for sure what happened however that situation is one thing and those thinking if they have a dual 40# bladder ,, they have 2 40# lifts available giving them 80#. I had not long ago someone asking me about htis saying theit thoughts were that if smaller is better to prevent a bubble form running top to bottom then they should have a dual and use one when submerged and then both when on the surface.

 

[broncobowsher]

A few years ago I got a sidemount setup with a dual bladder. I didn't pick it as one, it was a good offer from the shop owner's personal collection at a very good price.

I have never needed it, but I did play with it a few times. As supplied the inflator hose was way too short. Fixed that. It works. And now I just tuck the inflator out of the way. It is just a redundant option, like having 2 knives or 2 computers. I can deploy it faster than trying to use a SMB. No need to worry about connecting an inflator. Diving sidemount it is no big deal to do an oral inflate.

I have seen an inflator elbow come off in the water. A dual bladder would have made it from a treading water and about to dump weight into an add air and calmly abort. An "Oh Sh!t" moment into a "hold on a second" moment. But you can't just put it on and go. There is some practice and tuning needed, for me it was unusable as delivered.

Are there ways to not need it, yes. But there are times where it does make sense. If there is a floor that I can safely drop to, doesn't matter much. Drop, hit bottom, recover. But there are a few places where I have dove wet and didn't have a safe floor under me. That is about the only place it makes a lot of sense to me.

 

[broncobowsher]

there are certainly pros and cons to them. my only experience is one of observatoin. a dual bladder came into a shop both bladders had been used. one of them suposedly only once. the other was the primary bladder. It is guessed that from no use the unused bladder with moisture in it and being compressed by the primary bladder when stored caused the insides to bond, and when inflated tore. No one knows for sure what happened however that situation is one thing and those thinking if they have a dual 40# bladder ,, they have 2 40# lifts available giving them 80#. I had not long ago someone asking me about htis saying theit thoughts were that if smaller is better to prevent a bubble form running top to bottom then they should have a dual and use one when submerged and then both when on the surface.

Incorrect. The outer covering is the limiting factor. There is only space for 40# of lift. If one wing is full there isn't room for the other to inflate. Use one or the other. You do not get double the lift with a dual bladder. You get redundant inflation of the same space. Trying to use both at once and you are now managing an extra air space making life more difficult for no good reason.