Alternative to doubles

[Wookie]

What side mount and Independant doubles and weird configuration folks tend to forget is, when the world turns to crap on you (and someday it will), can you still get to the surface on what you have left? For your type of diving that you have specified, if the regulator on your main cylinder craps the bed, can you still make the surface on your 2 40's? I would say yes, it can work in the conditions you have described. What about when you decide on wreck penetration? Can you make it out of the wreck and to the surface on what you have left?

Most divers use manifolded doubles for a simple reason. They work. You can go on and on about how your back hurts, and your knees are weak and sidemount is easier on you, and at that point I would suggest that it's time to invest in a less physical sport, or get in shape. When a regulator fails on a manifolded double, you still have the use of all your gas. Yes, you can switch regs on Independant cylinders underwater, but it's a compromise. You are welcome to learn on a 120 with 40 stages, but at some point you will have to change configuration as you progress. Maybe to a rebreather.

 

[Queequeg]

My 120's are HP. I have thought of going to an lp tank and over filling it. My LDS will do it for it me, since I DM for them.

Addressing the question of the rule of thirds, how does a doubles setup, (my buddy using double 100's) have any more safety margin than I do? We both have 200 cu ft of air ( hp120 + two 40's) I thought it would be an advantage of mine since I can keep one stage for reserve, and customize my other stage for a deco gas, where my buddy can't. In regards to failures, I have 3 first stages right? And 4 2nd stages. I have two on my primary and one on each pony.

Our plan is not necessarily more bottom time, but more for safety. I suppose I should have stated that, we still plan on the dives being no-deco. I'm not so sure the extra 10minutes of bottom time I may get is worth the 30minutes of deco I'll need to do. However, some of the boat ops we are looking at to hit these wrecks we want to do require DP certification for dives to 150. Actually, just recently we were in Key West and the AN/DP certification was required to dive the Vandenburg without a DM, if you wanted to drop down below the deck. However, they stated they were no deco dives just the same. I suppose thats the same logic we are seeing on some of the wrecks we want to visit in the Atlantic also.

I guess thats where the confusion is setting in with me in regards to doubles. One particular dive we want to do sits at 140'. I have dove regulalry to 130 with al 80's when on live aboards or vacation without any pony. So I cant understand the reasoning for doubles to hit 150'. I dont know...maybe its my shortcomings.

I suspect when we start our Intro to tech class, AN/DP class here soon, I can bring this up to our instructor.

You all raise very interesting questions and points however. It certainly hasnt made it any easier for me, if anything its making my brain work even more, and on superbowl sunday...just isnt right!

 

[gsk3]

At times, I contemplate getting a set of doubles and a "proper" manifold, but I find myself often thinking about the complexity of such a rig.

As with most things in life, it's a matter of familiarity. I did a 20 foot shore dive with a friend yesterday, and darn if we didn't both shudder at the thought of diving singles. All those hoses coming out of one first stage!

That said, I did put the rig on to walk to the water and wonder if I'd forgotten to attach the tank....

 

[Mayor]

When forced to dive singles on vacation for non decompression diving I can be seen slinging an alum 40 as a stage. Anything with mandatory decompression will be in doubles. Like Ari said 20ft dive in doubles sounds perfect to me!

 

[Colliam7]

So therein lies my weighing of cost, function, and frequency. . . . As far as cost, I already have this equipment. I don't have doubles.

Ah, that explains a lot. I better understand your thinking - not so much that there is something 'wrong' with manifolded doubles as much as, 'What can I do with what I have?' Makes sense.

If we were eventually going to seek training and dives beyond 150' , I certainly then would be setting myself up with doubles.

And, who knows, you might get bitten by 'the bug' when you do AN/DP.

The subject of my dilemma really is we are talking 100-150' and not beyond that. It just seems I can use a 120, or larger, and sling a 40 for deco and 40 for reserve.

You can do just that. And, unless you somehow manage to build a really big deco obligation at 150' with your 120, a 40 should be fine, at least as far as accelerated deco goes. (I haven't done any simulations to get an idea of what you could do, perhaps others have.)

Thanks for clarifying.

 

[Colliam7]

The assumption is that the dive would be with doubles and one sling bottle of deco mix right? I thought it was a comparison of 3 bottles versus 3 bottles?

Looking at the oriignal post again, I think you are right, since he was referring to one slung deco bottle and one slung bottle for reserve. It would (presumably) be two back-gas tanks (with manifolded doubles) plus a slung deco bottle.

 

[waterpirate]

If you really beleive that you can stop at 150ish with less than 30 min BT, more power to you. After your explanation about frequency and adding a layer of safety, I would have opted for an adv rec triox rather than an/dp. This same place you are, I was 5 years ago. I came to the conclusion that if I could have stoped at 150, and 20 min of BT with 15 min of deco, the adv rec triox was the choice with single tank, stage, h valve.
I also beleive in the introduction of helium sooner than later as a layer of safety. Lowering the END for dives you do occasionally would do wonders for your problem solving abilities at depth.
Eric

 

[DaleC]

What side mount and Independant doubles and weird configuration folks tend to forget is, when the world turns to crap on you (and someday it will), can you still get to the surface on what you have left? For your type of diving that you have specified, if the regulator on your main cylinder craps the bed, can you still make the surface on your 2 40's? I would say yes, it can work in the conditions you have described. What about when you decide on wreck penetration? Can you make it out of the wreck and to the surface on what you have left?

Most divers use manifolded doubles for a simple reason. They work. You can go on and on about how your back hurts, and your knees are weak and sidemount is easier on you, and at that point I would suggest that it's time to invest in a less physical sport, or get in shape. When a regulator fails on a manifolded double, you still have the use of all your gas. Yes, you can switch regs on Independant cylinders underwater, but it's a compromise. You are welcome to learn on a 120 with 40 stages, but at some point you will have to change configuration as you progress. Maybe to a rebreather.

Who says we forget that? I can explain every every failure point and benefit of every rig I dive, sometimes better than someone diving a conventional rig who just "trusts" it will work out because that's what they were told to use. Please don't put words in someone else's mouth.

 

[gsk3]

And, unless you somehow manage to build a really big deco obligation at 150' with your 120, a 40 should be fine, at least as far as accelerated deco goes.

Well, the 40 of deco should be enough for most 150ft dives, and the 40 cuft of reserve gas should be enough to get you from 150 to 70. You're giving up on planning for second failure, though, since you can't easily share that 40 if your buddy loses their gas (more likely if they follow this configuration also) since it only has one reg. The most discussion that's related to this topic is on "team bailout" for rebreather teams. Go look up those discussions and see how you feel.

 

[DevonDiver]

What side mount and Independant doubles and weird configuration folks tend to forget is, when the world turns to crap on you (and someday it will), can you still get to the surface on what you have left?

I don't know the quality of the side mount and independant doubles, or other weird configuration folks you deal with... but all the ones I know don't tend to forget such things... not for a second. Without wanting to sound pedantic, but are you aware of the training given for equipment such as sidemount?

Well, the 40 of deco should be enough for most 150ft dives,

...and if you have to share with a buddy who's lost their deco gas?

..and the 40 cuft of reserve gas should be enough to get you from 150 to 70.

..and if you have to share with a buddy who's lost their back gas?

You're giving up on planning for second failure, though, since you can't easily share that 40 if your buddy loses their gas (more likely if they follow this configuration also) since it only has one reg.

Exactly

The OP is wanting to formulate a configuration in preparation for technical training/diving based upon their existing recreational perspectives. He's being informed of the drawbacks by those with technical training and diving experience, but is now choosing to disregard it.

Several of those who are advising the OP otherwise aren't technically trained divers. Read into that what you will.

not so much that there is something 'wrong' with manifolded doubles as much as, 'What can I do with what I have?'

To which the answer is: not much.

To which another answer is: make compromises and take unnecessary risks on technical dives, because you aren't willing to make the financial commitment that technical diving requires.

I do think I understand what the OP is thinking. It comes across as something like this: It's only shallow, within recreational range... with 'light' deco... so it's not really 'tech' huh? It's at recreational depths, so a recreational approach is satisfactory... but I can sling on a few pony cylinders as a token gesture towards having a 'tech' approach. Most importantly, get the necessary 'card' so I can book boat trips. Select the options with the most convenience and cheapest investment and then go do some dives in the assumption that technical diving principles don't need to be applied because of the depth/demands of the dives. Make further assumptions that nothing will go wrong, ever, and that the full spectrum of risk mitigating equipment and procedures aren't needed or applicable.