Why do the big OMS wings have 2 inflators?

[cool_hardware52]

Hi Tobin,
They are overweighted because in addition to back gas and deco bottles, they generally carry an assortment of tools to pry, chisle, saw, and/or cut away "treasure"

That's not what Lucy's Diver claimed here

And guess what - at 300 PSI in 15 FSW I can barely hold depth with this configuration, so I am not over weighted.

Tobin

 

[cool_hardware52]

I'll restate my position.

If a diver using a Drysuit + conventional wing is weighted so they are negative by the weight of their backgas + 2 lbs their drysuit can provide redundant buoyancy.

Will this work if the diver is grossly over weighted?

No, but there are better means to manage "other" negative items.

Tortured constructs that involve 3 or 4 or more failures or bad practices serve only to highlight the merits of simplicity.

Tobin

 

[Lucy's Diver]

And my position is that a second bladder adds redundancy with so little additional gear or training its akin to an airbag in a car. Airbags in cars would deploy a lot less often if nobody engaged in bad driving practices and suffered no instances of multiple equipment, road, and other driver failures. These tortured constructs serve only to highlight the advantages of simplicity in driving and the need to avoid bad driving practices. Yet this also ignores reality.

When you're in the water floating can become really important really fast. Even pretending that a drysuit offers true redundant bouyancy, I can live with a triply redundant system with no real negative.

I just yet have to hear the down side to a redundant bladder other than the fact that is violative of a certain minimalist philosophy. I just don't buy that philosophy; to a certain extent I can't since I have to dive mutiple systems with multiple configurations for different jobs. I simply cannot dive the same stuff all the time, but that aside I just cannot understand why this is such a debate. Floatation is an issue that needs redundancy, and to me a double bladder is the only system for true redundancy in a heavy doubles configuration, and it provides this redundancy without sufficient disadvatages to make one consider not using it.

 

[cool_hardware52]

When you're in the water floating can become really important really fast. Even pretending that a drysuit offers true redundant bouyancy, I can live with a triply redundant system with no real negative.

I just yet have to hear the down side to a redundant bladder other than the fact that is violative of a certain minimalist philosophy. I just don't buy that philosophy; to a certain extent I can't since I have to dive mutiple systems with multiple configurations for different jobs. I simply cannot dive the same stuff all the time, but that aside I just cannot understand why this is such a debate. Floatation is an issue that needs redundancy, and to me a double bladder is the only system for true redundancy in a heavy doubles configuration, and it provides this redundancy without sufficient disadvatages to make one consider not using it.

The logic behind the Drysuit as redundant buoyancy:

Most "bigger" dives demand a drysuit as the thermal protect provided by a compressed wetsuit is insufficient.

This drysuit can, with no other added complexity, provide redundant buoyancy as long as the diver is not over weighted.

Drysuits present their own risks and benefits, but the risks can be balanced against the benefits of both improved thermal protection and redundant buoyancy.

You can dismiss the risks associated with a redundant bladder wing, but they are "non zero" and can only be measured against the single benefit of redundant buoyancy.

Tobin

 

[Standingbear56]

That's not what Lucy's Diver claimed here



Tobin

Hello Again,
Lucy's Diver isn't the only wreck diver in the North East, and I sincerely doubt he would claim that his training and experiences speak for all the NE wreck divers. The fact is simply this: Neither you (Tobin), nor DIR advocate a secondary bladder, and there are valid reasons for this point of view. However, that does not mean that secondary bladders aren't used or shouldn't be used. The fact that they outsell single bladder wings 2:1 (at least in our experience) is something that isn't going to go away. Also take into account that the majority of the world's divers are not DIR (not a put down to DIR, just a fact) and you have an interesting coincidence - Yes? While checking on the main CMAS website CMAS - ConfñÅñÓation Mondiale des ActivitñÔ Subaquatiques - PORTAIL, under "Technical Committee", it appears that they also advocate a double bladder BCD when not using a drysuit for their technical courses. So now we have not one, but two major training agencies who are saying that there is a need for a dual bladder under certain conditions. I also found this article by Karl Shreeves (PADI):

"A fully equipped, properly weighted tec diver may be as much as 20 to 50 pounds negatively buoyant at the start of a dive. Why? Because that's the weight of just the gas in the full cylinders.

Therefore, a tec diver needs at least two ways of controlling buoyancy a primary and a backup. Since you can add air to a drysuit, some individuals suggest that a double-bladder BCD essentially two BCDs in one is unnecessary if you tec dive in a drysuit.

While this may work in some situations, it doesn't stands up as a universal practice. Most drysuit manufacturers will tell you that their suits weren't designed for the stress of being filled enough to offset 20 or more pounds negative buoyancy. Even diving dry, then, you often need a double-bladder BCD. Unfortunately, some divers believe otherwise and they're often wrong.

If you think you only need a single-bladder BCD, find out. Do this: Kit up in all your tec gear with full cylinders and properly weighted (i.e., able to maintain a 15-foot decompression stop wearing near-empty cylinders). Go into a shallow, benign environment. Deflate your BCD and then attempt to ascend and maintain a deco stop at 15 feet by hovering for 15 minutes using only your drysuit to control buoyancy. Do some gas switches. Share gas with a partner. Go through all the primary and emergency procedures that apply to tec diving using only your drysuit to control buoyancy. Assume a head-up position to be sure most of the air doesn't simply escape around your neck (which would mean you can't be vertical in a backup buoyancy emergency).

Now ask yourself whether you could reasonably expect to handle a failed BCD using only your drysuit while task-loaded with decompression and the stress of failed equipment. Even if you could, what would be the more reasonable way to manage the emergency?

When you're done, you'll know whether you need a double-bladder BCD for open water, heavy-weight diving. Chances are, you will".

Tobin, I know that with your knowledge of BP/Ws, you can match anyone, and I have no doubt that a discussion of this issue between you and Karl would be one for the books. I know that I for one would certainly sit back and take alot of notes. However, Karl is a major player of the world's largest training agency, so regardless of how many disagree, there is a ton of clout here. This is not including CMAS.
I have personally taught students with dual bladder BCDs, and have dove with many divers who use them as a standard part of their kit. Never in my own personal experience, nor in that of many divers I have dove with, who utilize one correctly have they caused a problem. However, there were a few times where there was a primary BCD failure, and the backup bladder carried the diver safely through.
My personal position is this: If someone has a dual bladder BCD, I'll teach them the proper way to utilize it. If someone has a single bladder one, the same thing goes. One should be familiar with the other and if at all possible be able to try the other style out so that they are at least familiar with it. Then let them make their own decision.
Take care,
George

 

[cool_hardware52]

Hello Again,
Lucy's Diver isn't the only wreck diver in the North East, and I sincerely doubt he would claim that his training and experiences speak for all the NE wreck divers. The fact is simply this: Neither you (Tobin), nor DIR advocate a secondary bladder, and there are valid reasons for this point of view. However, that does not mean that secondary bladders aren't used or shouldn't be used. The fact that they outsell single bladder wings 2:1 (at least in our experience) is something that isn't going to go away.

Popularity and sales numbers do not confirm the fitness of any product, they are primarily a measure of marketing prowess.

For example Subprime / Alt A real estate loans have been very popular in the recent past, and have proven to be unwise.

Various agencies teach all manner of things I do not agree with.

Diving grossly over weighted is near the top of the list.

Tobin

 

[Standingbear56]

If this same diver actually keeps diving doubles, and actually reaches the point where they are doing longer exposures they will quickly find they do actually need a drysuit. Now they are in the "hole" by $300-400 more than they would have been if they had avoided the redundant bladder wing and purchased a good quality conventional wing and drysuit.

Tobin[/QUOTE]

Hi Tobin,
I agree with you totally that an overweighted diver is indeed an accident waiting to happen. As I stated previously, I tried it myself just to see, and had very negative (pun intended) results.
With the understanding that you do not endorse dual bladder and have valid reason for that point of view, I have highlighted some of the issues you have presented and will attempt to answer how the dual bladder divers here deal with the issues.
What ever "failed" the first bladder probably also failed the second.
Seldom true - the most common problem is the damage to the elbow attaching the corrigated hose to the bladder. Failure in one does not mean there will be a failure in the back up bladder.
Added complexity. With a conventional wing + drysuit you have redundancy and the added benefit of a better exposure system.

Added complexity is a relative thing. With the amount of gear and redundancy that the average technical diver carries, an uninflated bladder, hose and LPI that are tucked away is really no problem. It accounts for very little drag increase, and as to it's complexity - if a diver cannot handle a back up bladder, how do they handle their primary one, since with the possible position of the hose are exactly the same. The hose position is delt with by training and practice. If your drysuit is comprimised, you still have redundant buoyancy. The exposure systems of these divers is generally top of the line and no one has comprimised any other system of their kit for the sake of a dual bladder.

Big (High lift) wings imply long exposures. One only needs huge tanks and thick buoyant exposure suits if they are going deep, or long or both.

Long exposures, or shorter exposures in cold water combined with long hang times equal large gas supplies along with deco bottles. This is big part of technical wreck diving.
Long Exposures simply are not the well served by a wetsuit. Wetsuits compress and loose thermal protection, not what you need for a long exposure that very likely involves deco.
Total agreement here. However I've seen divers in tropical waters do just that.
IMO redundant bladder wings are a great way to make your drysuit more expensive.
Please show me who bases the price of a drysuit dependent on what style of wings a person is going to use? I do understand the point you are trying to make, but it really isn't an issue.
The "new to doubles" diver who can't afford or can't yet justify ~$3K for a drysuit decides to keep their wetsuit and buy a $600-700 redundant bladder wing.
Only a "new to doubles" diver in need of a new instructor and/or LDS.
"With my magic double bladder 100 lbs lift wing I don't need to stinking drysuit!"
I repeat - Only a "new to doubles" diver in need of a new instructor and/or LDS.
If this same diver actually keeps diving doubles, and actually reaches the point where they are doing longer exposures they will quickly find they do actually need a drysuit. Now they are in the "hole" by $300-400 more than they would have been if they had avoided the redundant bladder wing and purchased a good quality conventional wing and drysuit.

If they are trained and outfitted properly, they would have the drysuit from the start. Again this isn't an issue here at all.
I guess we both can agree to disagree and there shouldn't be a problem with that. I certainly do not expect you to convert to a dual bladder junkie any more than you can expect me to not say dual bladders do have a place in diving, especially with the fact that both agencies I teach for do indeed utilize dual bladder BCDs. In the end, it's simply a matter of choice, with both sides having valid points. On one point we definitely agree on is the size of the wing. Most technical divers can make do with 50 - 60 lbs maximum lift. Even those numbers are questionable. I have yet to see someone truly need a 94 lb lift. I will however ask my agencies for their experiences and reasonings, and see if I can find the why's behind the decisions.
Happy & Safe diving,
George

 

[GrandpaScuba]

I do not use a double bladder.
That said.... I think you miss the point.
with double bladder, you only use one inflator (one bladder), if you get auto inflation or the hose opens up etc. then you use the other one. Its there only as backup, sort of like that backup reg on your doubles.

I dive only one bladder also. The only time it failed was when a sharp object pierced through one side of the bladder and out the other side. With a redundant bladder, both would have been toast.

 

[Lucy's Diver]

Popularity and sales numbers do not confirm the fitness of any product, they are primarily a measure of marketing prowess.

For example Subprime / Alt A real estate loans have been very popular in the recent past, and have proven to be unwise.

Various agencies teach all manner of things I do not agree with.

Diving grossly over weighted is near the top of the list.

Tobin

That's two overbroad statements in one. Its not the sub prime loans that were the problem, its the securitization pipeline ending at the Dutch auction.

There are plenty of dives where there's just no way to jump in without being grossly over weighted. Tech people need the air they need, period. Big tanks weigh what they weigh. I non neoprene drysuit on a non fat guy ain't gonna float twin 120s and a set of slung 40s.

 

[cool_hardware52]

That's two overbroad statements in one. Its not the sub prime loans that were the problem, its the securitization pipeline ending at the Dutch auction.

The point stands, demand alone does not validate any product or process. There's fair demand for illegal drugs too.

There are plenty of dives where there's just no way to jump in without being grossly over weighted. Tech people need the air they need, period. Big tanks weigh what they weigh. I non neoprene drysuit on a non fat guy ain't gonna float twin 120s and a set of slung 40s.

Many would disagree. Advocating diving grossly over weighted, when it is easily avoidable is, in my opinion, irresponsible.

Tobin