double tank equipment

[DaleC]

What's so hard to understand.

Some people have the balanced opinion that, while formal training can make things go quicker, many parts of scuba are easily attainable by a capable learner via alternative means.

One of the first stupidish questions I asked in the DIR forum was whether it was possible to dive solo DIR style. It actually was a pretty good discussion considering. Since then I have dived solo a lot and learned quite a bit about DIR (even taken GUE Fundies). We shouldn't assume too much by the first question a person asks about a subject.

Here's that thread: http://www.scubaboard.com/forums/dir/268825-dir-process-system.html

 

[Storker]

Where in the process of learning to dive proficiently to 130 ft (~39m) in a single tank does a diver learn what they need to know to do the same dive in big double steel tanks?

But now you're either moving the goalposts or assuming without evidence.

The discussion was about doubles, not big doubles. And I was specifically addressing smaller doubles.


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---------- Post added June 18th, 2015 at 07:00 AM ----------

Is it good practice, or irresponsible to assume the OP is surrounded by qualified mentors when there is zero evidence to suggest that is the case?

Is pointing out that as long as one stays within rec limits, there is no deep fundamental difference between a small doubles set and a big single "encouraging irresponsible behavior"?


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[Adobo]

But now you're either moving the goalposts or assuming without evidence.

The discussion was about doubles, not big doubles. And I was specifically addressing smaller doubles.

Actually, you are the one moving the goal posts. You are looking at corner cases in order to support your position rather than looking at the question as it relates to the OP and as it relates to the bigger community of people who might read this thread for reference.

The OP is does not give details as to the size of doubles. Yet you present a use case where smaller doubles can be, in relative terms, just as benign to a recreational dive as a large single tank. While true, I offered the counter point of large doubles are not benign for wet suit divers when diving to depths as shallow as even 30meters.

Are there really any inexperienced divers putting together doubles using tanks with smaller than 80 cu ft (11 liter) tanks? I don't see any here in Northern California (either at the dive shop that does all the nitrox and trimix fills), at the dive sites in Monterey or Carmel, CA. I did not see anything smaller than double 100s in the top tech dive shop in Vancouver, BC. In fact, they usually recommend double 130s to their divers. Double al80s is what I've seen in Mexico. In Florida, I've seen double HP130s, LP104s and LP95s. I've read about some divers in Florida using double LP85s in caves and double al80s in the ocean. The only exception I have seen is a set of LP72s that a friend of mine owns. And those tanks only come out diving once in a blue never.

So based on what I have seen, the safe bet is that the doubles either the OP or any subsequent reader of this thread will be doubles that are at least 80cu ft tanks or bigger.

 

[cool_hardware52]

Is pointing out that as long as one stays within rec limits, there is no deep fundamental difference between a small doubles set and a big single "encouraging irresponsible behavior"?

Can you direct me to a single example of a diver asking how many SPG's they need for a "big single"?

After that we can discuss how there is no difference between small doubles and a big single.

Tobin

 

[Adobo]

Very. Clever. Editing. I think the reality is that you are out of facts, very short on practical information with only moderate experience and bereft of any logical consistency. A formalistic zombie with the zeal of a convert.

Writing that everything is incorrect without any specificity suggests a limited knowledge base and a tiny mind. What's your position on triple and quadruple tank set ups?

Perhaps you know more about reef tanks. I have a couple now, the oldest set up since the 1980s. Lee Chin Eng was one of my early mentors when I was seriously into them. These days simplicity and natural processes prevail.

Here is what I know about the reef tank hobby - it is the only recreational activity that I know of that has just as much people posing as "experts" as scuba. And just like scuba, they drop names and drop their years of experience as if that gives credibility to their arguments. And just like scuba, they resort to logical fallacies to support their arguments.

Despite your ad hominem attacks, I am not particularly motivated to illustrate for you what you clearly refuse to see. But to humor you, I will give you just one example. You state:

Weighting properly for doubles is largely a matter of achieving proper buoyancy with tank(s) filled, and anticipating the difference when tank(s) are down to whatever minimum is applicable. Again, this is absolutely basic stuff, and no one should be certified without that skill and knowledge.

If that diver puts together a set of double 130s, fills it with 32% and wants to dive this rig to 100ft (30 meters) in the ocean while wearing his 7mm farmer john. Is this a good idea or a bad idea? What are the gotchas for this dive? It's not a hypothetical. I've watched someone do this.

P.S. My only experience with triple, quadruple and quintuple (is that how you say five?) tanks is using stages and deco bottles with backmount doubles. These configurations are not that uncommon in tech and cave diving. I have no experience in sidemount, independent doubles or the convoluted set ups that world record depth divers use.

Anyway, my position on it is this, someone who doesn't have knowledge and is wanting to do dives that require 3, 4 or 5 tanks, it is absolutely imperative that the diver get proper training.

 

[Storker]

Actually, you are the one moving the goal posts.

No, my goalposts have been fixed all the time. Again, it's not the number of tanks that counts, it's the amount of gas. Now, if the reaction to the OP had been "what kind of doubles?", and "why do you want to dive doubles?" the case had been different.

There may be several possible reasons for asking about doubles:

• The OP might just have been curious. At which point a simple answer to their question wold have been appropriate.
• The OP might have a high SAC rate and wanted to carry more gas within rec limits. In which case a doubles set may or may not be appropriate, but work on better trim, buoyancy and behavior might well be a cheaper way to extend the bottom time.
• The OP might have heard the fact that doubles give you a COG closer to your back, with less tendency for the diver to turn turtle, compared to a large-ish steel single. In which case a doubles set may very well be appropriate.
• The OP might want to carry tons and ton of gas which could last them well into deco county. That, then, would be a case for concern, because deco diving is tec, and requires proper training, ability to close a post and the manifold, to be able to sort out problems without bolting for the surface, and all the other stuff I don't know since I dive rec only.

Instead, the reaction was closer to "Doubles!!!!!1111!!! OMG, you're going to die!!!1111!!!", and my pointing out that doubles don't necessarily mean full tec was "encouraging irresponsible behavior". Oh well.

You are looking at corner cases in order to support your position rather than looking at the question as it relates to the OP and as it relates to the bigger community of people who might read this thread for reference.

No, I'm looking at the world as it looks from our side of the pond. Doubles are very common both in Scandinavia and in the UK, also for rec diving, and that fact should well be known to "the bigger community" AKA you guys on the west side of the pond, who seem h€ll-bent on insisting that doubles=tec.

Can you direct me to a single example of a diver asking how many SPG's they need for a "big single"?

What are you shooting for here? Why is that relevant to my point?

After that we can discuss how there is no difference between small doubles and a big single

There is a difference. But the difference isn't big enough to justify the claim that a simple statement that doubles may be quite appropriate for rec diving (depending on the type of doubles) and that doubles don't necessarily require formal training to use safely (depending on how the gear is used) is "encouraging irresponsible behavior".

But since it looks as if I'm flogging a dead horse here, I'll leave you guys to your opinion that a double set is something fundamentally different from a single tank rig.

---------- Post added June 18th, 2015 at 08:26 AM ----------

my position on it is this, someone who doesn't have knowledge and is wanting to do dives that require 3, 4 or 5 tanks, it is absolutely imperative that the diver get proper training.

Which is a position that also I wholeheartedly agree with.

 

[Adobo]

No, my goalposts have been fixed all the time. Again, it's not the number of tanks that counts, it's the amount of gas.

In my opinion, that is still wrong. But we will just have to agree to disagree.

There may be several possible reasons for asking about doubles:

• The OP might just have been curious. At which point a simple answer to their question wold have been appropriate.
• The OP might have a high SAC rate and wanted to carry more gas within rec limits. In which case a doubles set may or may not be appropriate, but work on better trim, buoyancy and behavior might well be a cheaper way to extend the bottom time.
• The OP might have heard the fact that doubles give you a COG closer to your back, with less tendency for the diver to turn turtle, compared to a large-ish steel single. In which case a doubles set may very well be appropriate.
• The OP might want to carry tons and ton of gas which could last them well into deco county. That, then, would be a case for concern, because deco diving is tec, and requires proper training, ability to close a post and the manifold, to be able to sort out problems without bolting for the surface, and all the other stuff I don't know since I dive rec only.

Instead, the reaction was closer to "Doubles!!!!!1111!!! OMG, you're going to die!!!1111!!!", and my pointing out that doubles don't necessarily mean full tec was "encouraging irresponsible behavior". Oh well.

Yeah, its terrible that people overreact and are so eager to tell others that they are going to die. Could you point me to where anyone did that on this thread?

---------- Post added June 17th, 2015 at 11:53 PM ----------

No, I'm looking at the world as it looks from our side of the pond. Doubles are very common both in Scandinavia and in the UK, also for rec diving, and that fact should well be known to "the bigger community" AKA you guys on the west side of the pond, who seem h€ll-bent on insisting that doubles=tec.

Uh... take one minute and read the first 10 posts in this thread. Not only did Tobin give the direct answer to the OP's question on the second post, Tobin is also explicit about some of the things that recreational divers need to consider when diving doubles in post #9. He is also very clear in that post that he is not referring to trimix training (or in your words, tec).

You're bent out of shape because you think people are equating doubles to tec diving. You are the only one who keeps bringing that up over and over again. Read the first 10 posts again. That's not what he said said.

And just so you don't think that I am some kind of Tobin sycophant, I'm not. In fact, I am kind of bitter towards the guy. He always leaves me feeling stupid when I ask him about cheaper lithium scooter batteries.

 

[DaleC]

If that diver puts together a set of double 130s, fills it with 32% and wants to dive this rig to 100ft (30 meters) in the ocean while wearing his 7mm farmer john. Is this a good idea or a bad idea? What are the gotchas for this dive? It's not a hypothetical. I've watched someone do this.

But according to what Agilis said, there is no difference. If a thick wetsuit diver used a single 130cuft tank to dive to 100 feet they would encounter the same issues of compression and lost buoyancy, only to a lesser degree. They still have to consider their weight vs available lift.

 

[cool_hardware52]

There may be several possible reasons for asking about doubles:

• The OP might just have been curious. At which point a simple answer to their question wold have been appropriate.
• The OP might have a high SAC rate and wanted to carry more gas within rec limits. In which case a doubles set may or may not be appropriate, but work on better trim, buoyancy and behavior might well be a cheaper way to extend the bottom time.
• The OP might have heard the fact that doubles give you a COG closer to your back, with less tendency for the diver to turn turtle, compared to a large-ish steel single. In which case a doubles set may very well be appropriate.
• The OP might want to carry tons and ton of gas which could last them well into deco county. That, then, would be a case for concern, because deco diving is tec, and requires proper training, ability to close a post and the manifold, to be able to sort out problems without bolting for the surface, and all the other stuff I don't know since I dive rec only.

Based on the Original Post we have *zero* evidence to assume *anything* about his motives or intentions, zero.

It's quite possible the OP could be considering something risky *without* being aware of the risks. No way to certain of this, but it is among the possibilities.

Where is the risk in recommending competent training? I'd suggest such advice reduces the chances the OP gets hurt.

Now lets compare that to your philosophy that doubles are no different from a big single.

Which has the greater chance of leading to grief? Please be specific.

Tobin

 

[victorzamora]

Again, it's not the number of tanks that counts, it's the amount of gas.

It's absolutely the number of tanks that matters. I can go dive a single 40 or a giant LP120 pumped to 163ft of gas. One holds four times more air than the other. The difference? I need fills less often on the big one. As long as you watch your computer (or tables), nothing changes. When you dive two tanks, your configuration changes. There are questions that, without an unreasonable amount of work or shared experience, simply can't be answered alone. I'm not saying you have to pay money for a dedicated "doubles course." I'm saying that you need guidance beyond "just one SPG" if you have to ask how many SPGs go on doubles.

No, I'm looking at the world as it looks from our side of the pond. Doubles are very common both in Scandinavia and in the UK, also for rec diving, and that fact should well be known to "the bigger community" AKA you guys on the west side of the pond, who seem h€ll-bent on insisting that doubles=tec.

Storker, doubles aren't tec.....that's fine. I don't know what it is with you, but when someone thinks of the word doubles you immediately jump to yelling about that not meaning "tech." I agree with you. However, that's not the issue being raised here. OP asked about how many SPGs for doubles. Clearly, the OP is in need of more guidance than "typically just the one."

There is a difference. But the difference isn't big enough to justify the claim that a simple statement that doubles may be quite appropriate for rec diving (depending on the type of doubles) and that doubles don't necessarily require formal training to use safely (depending on how the gear is used) is "encouraging irresponsible behavior".

Tobin and I have said repeatedly that FORMAL TRAINING isn't what he was suggesting as required. It was simply further help. A good dive buddy, a mentor, a very competent and helpful dive shop, a friendly diver at the pool....whatever. You can't just bungee doubles to a stab jacket and hand them to every OW diver and expect them to do well. To me, it's the same as a sidemount system.