Doubles?

[avra cohen]

Matt is correct. In the event you had a burst disc failure, you would have to be able to isolate to prevent you form losing all your gas.

As I am just moving up to doubles this thread has been particularly timely.
My tech instructor is a world class diver, published author, big dives... Doria, cave exploration, etc.
While advocating flexibility in choosing various configurations under different circumstances, I was surprised to learn his personal preference. He dives manifolded doubles but with the isolator CLOSED, diving them as independent doubles.

His vast experience notwithstanding, this sounded kind of nuts to me, simply because I had never heard of the practice in my fairly extensive reading. After following this discussion, it actually now seems like a way to reap the benefits of both systems.
Half the gas is saved as the default, no action required. But all the gas can be accessed in the event of the far more probable regulator failure.

Has anyone else heard of this? What do you think about it?

Avra

 

[USMCRet]

Instead of diving "doubles", you may also want to look into sidemount diving....

USMCRet

 

[Matthew Mandziuk]

Your consumption rate is one thing, but you also want to look at a few other things.

You mentioned the USD j-valve system.....They called it a suicide manifold for a reason. I single outlet manifold is not the safest or best choice for diving.

A single 130 with an H-valve will more than suit your needs, however, you will have to commit to an independent first and second stage regulator system.

I'd suggest getting a right or left hand elbow, so you can have an opposite on your 2nd tank so you can double up if you eventually go the route of double tanks.

The other way that is cheaper is to lower your work of breathing.

I don't know how much weight you wear, but I typically shed 5-12lbs per student on peak performance buoyancy on my advanced o/w course.

In addition to that, most divers don't count their air intake and outgas, in that they don't pay attention to how long the breath in and out for. Count your inhalation and exhalation. 8 seconds in, 8-12 out is standard.

 

[avra cohen]

So a 15 years old sees diving as adventurous and wants to dive doubles. Great! We need a lot more of that not less and I'd encourage more people to encourage such obviously rampant irresponsibility in our youth - because it is a lot healthier than most of the alternatives.

This is the manifold for which our intrepid teenager is currently attempting to tender an offer on this web site.

http://www.scubaboard.com/forums/4234343-post1.html

Would you be comfortable with your 15 year old diving with this equipment?
That a new diver is looking to make this the foundation of his kit, does not instill in me the confidence that he understands fundamental aspects of gear configuration and equipment selection.

As I am just moving to doubles myself, I cannot offer expertise born of experience.
But I certainly know that there are weighting issues that must be given full consideration. With his experience level, it would be hard to imagine his having mastered the nuances of diving dry. So are we to encourage our enthusiastic young diver to double up a set of steel 120's with an antique manifold (not that it would fit, mind you) and go into OW diving wet?

Obviously not. We know better. But does he? Does he understand the need for redundant buoyancy? The concept of a balanced rig? Can he shoot a bag reliably? Do an S-drill and a valve shutdown? Unless that is a loud affirmative across the board, this kid has no business being in doubles yet. Except possibly under the very watchful eye of a mentor qualified to impart all the aforementioned knowledge and skills.

My advice to you John is to dive safe and dive often in varied environments and under various conditions. MASTER your buoyancy skills in a single tank rig. If you haven't already, move to a backplate and wings. Invest your $$$ in a pair of top drawer regulator sets. Get an H-valve on a steel tank and you will have all the essential elements to learn and practice the skills you will need going forward. Read everything you can about diving and about the theory and practice of different equipment configurations. MASTER dive planning and gas management. Practice safety and rescue skills. Find an instructor you feel comfortable with and pursue training incrementally. Develop buddies that share your enthusiasm and are willing to commit to training.

And of course... have FUN!

Just my two cents... Avra

 

[kidsdream]

For $125ish you can get a nice used current generation manifold. Look around lots better ways to go and service kits will be readily available.

This is the manifold for which our intrepid teenager is currently attempting to tender an offer on this web site.

http://www.scubaboard.com/forums/4234343-post1.html

Would you be comfortable with your 15 year old diving with this equipment?
That a new diver is looking to make this the foundation of his kit, does not instill in me the confidence that he understands fundamental aspects of gear configuration and equipment selection.

 

[UCFKnightDiver]

WOW, by looking at that manifold you are trying to buy I can tell you one thing SLOW DOWN, get expirience, dive with people more expirienced than yourself, I dont know anyone who is or would use a manifold like that anymore, much less that manifold may not/probably not fit the current threading on tanks today.

 

[rstofer]

WOW, by looking at that manifold you are trying to buy I can tell you one thing SLOW DOWN, get expirience, dive with people more expirienced than yourself, I dont know anyone who is or would use a manifold like that anymore, much less that manifold may not/probably not fit the current threading on tanks today.

I would use that manifold if I didn't already have one that is quite similar. The center outlet is perfect for a double hose regulator. Isolation was never a consideration and the J feature is optional if an SPG is attached. Since each tank outlet has a dedicated burst disk, I wonder if that manifold has a port for an SPG? It certainly looks like it.

My guess is that that specific manifold is designed for 6.9" diameter tanks like the Al 50 or the old LP 72. It appears to have 3/4" threads so that shouldn't be a problem. I wouldn't bet on it working with any modern tanks of 7.25" or 8" diameter. The manifold, bands and tanks all need to match.

My specific manifold also has a post valve on one end in addition to the center outlet. By orienting the manifold backwards, the post winds up on the left side where a first stage can be mounted and used to provide LP inflation and an octo. But still no isolation...

If the goal of doubles is, as the OP states, very long but shallow dives with no overhead (physical or virtual) then all the isolation and double regulators just isn't an absolute requirement. In effect, this type of manifold does one thing: it increases gas capacity. The diver still has the same single regulator they would have if they bought a HP 250 (if one were made). We see divers all the time buying HP 130s because Al 80s are too small, so what's the difference? It's still a single tank with a single outlet for a single regulator. No more or less redundancy than any other OW recreational diver with a single tank and regulator.

The real problem is tank selection. It would be better to use tanks that aren't highly negative in that a wing failure might be survivable. But this is an entirely different discussion.

Now, just for the record, I don't recommend doubles. I can't carry the weight and I don't do the types of dives that require either the redundancy or the volume. But, if I were building up a set of doubles with something like HP 120s, I would use a proper manifold (and this isn't it!) with double regulators, a high lift wing and probably a drysuit for redundant buoyancy.

I also think that doubles are a topic for divers with well over 100 dives. I know, someone will chime in with the fact they did their OW checkout dives with doubles but I still think it is an advanced topic. Not the kind of thing a beginning diver needs to get involved with.

So, yes, I would dive that manifold. But, no, I don't recommend it unless it used with a double hose regulator. Double hose regulators are a lot more fun than single hose.

Richard

 

[Green_Manelishi]

As I am just moving up to doubles this thread has been particularly timely.
My tech instructor is a world class diver, published author, big dives... Doria, cave exploration, etc.
While advocating flexibility in choosing various configurations under different circumstances, I was surprised to learn his personal preference. He dives manifolded doubles but with the isolator CLOSED, diving them as independent doubles.

His vast experience notwithstanding, this sounded kind of nuts to me, simply because I had never heard of the practice in my fairly extensive reading. After following this discussion, it actually now seems like a way to reap the benefits of both systems.
Half the gas is saved as the default, no action required. But all the gas can be accessed in the event of the far more probable regulator failure.

Has anyone else heard of this? What do you think about it?

Avra

Heard of it.

Lots of variables and questions to ask.

Is your instructor "saving" the non-used cylinder, effectively limiting his/her dive to the contents of the in-use cylinder? Either the instructor has a low SAC, carries large tanks or makes short dives. It's also possible the instructor is switching regs during the dive to keep both sides "evenly" drained of gas. Personally, I am not keen on unnecessarily removing a regulator simply to switch to another gas source. I prefer to keep a working reg in my mouth. On the other hand, your instructor might do a lot of solo diving and have no buddy from whom to acquire gas in event of blowout.

 

[DA Aquamaster]

This is the manifold for which our intrepid teenager is currently attempting to tender an offer on this web site.

http://www.scubaboard.com/forums/4234343-post1.html

Would you be comfortable with your 15 year old diving with this equipment?

Absolutely. It is probably THE best way to get into doubles. It has only a single reg so the configuration change is minimal while you master the mass, buoyancy and swing weight issues that come with doubles. Then once you accomplish that, go with an isolator manifold and worry about valve drills (which is after all an overhead environment concern, not a recreational diving concern) and the other tech aspects of doubles.

The current "gotta be tech to dive doubles" fad has served only to greatly steepen the learning curve of divers who aspire to be tech. Divers, based on such "sound" advice, end up trying to do it with very new and unfamiliar doubles and a related tech configuration with consequent difficulties mastering all the skills involved at the same time.

I came up the other way with single outlet doubles and later transitioned to independent doubles and eventually isolator manifolded doubles when my diving changed and they made sense. None of those transitions were difficult as they all built on solid experience with single outlet doubles.

That a new diver is looking to make this the foundation of his kit, does not instill in me the confidence that he understands fundamental aspects of gear configuration and equipment selection.

Frankly a lot of divers cause me to have that concern. The ones that really worry me the most are not the ones that ask questions but rather the ones that think they know the answers because they heard it from an instructor or read it in a text book and have only minimal real world experience to base their opinions on. That stage where they think they know a lot (or in extreme case know it all) when they don't is without question the most dangerous stage of a diver's development as they don't know enough to know what they don't know and sometimes it kills them.

As I am just moving to doubles myself, I cannot offer expertise born of experience.

Noted.

So are we to encourage our enthusiastic young diver to double up a set of steel 120's with an antique manifold (not that it would fit, mind you) and go into OW diving wet?

I reviewed his 11 posts and none mentioned 120's so let's not catastrophise the issue. The manifold in question was/is intended for double AL80's (but would fit any 7.25" dia set of doubles) and double AL80's are affordable, buoyant, offer a decent amount of gas deeper rec dives or two shallower rec dives and are not a wasted purchase when you move up to tech as they make good stage bottles.

Does he understand the need for redundant buoyancy? The concept of a balanced rig?

Do you? An HP 130 is 11 pounds negative when full and a Faber 120 is 16 pounds negative, but no one screams "OH MY GOD HE IS GONNA DIE!" when a recently minted diver straps one on. Double AL 80s in comparison are about 9 pounds negative including the bands and manifold. Consequently, with double AL80's a balanced rig is easy to achieve even in a wet suit and the need for redundant buoyancy is a largely moot issue.

Now that you have some specific facts to consider, which one would you rather see a new diver use?

Can he shoot a bag reliably? Do an S-drill and a valve shutdown?

It doesn't matter at that level.

Unless that is a loud affirmative across the board, this kid has no business being in doubles yet. Except possibly under the very watchful eye of a mentor qualified to impart all the aforementioned knowledge and skills.

Wrong. See all of the above. You are confusing using doubles with techncial diving and the two are separate and distinct skills. Again, a lot of aspiring tech divers would be well served by starting out in single outlet manifolded doubles and gaining valuable experience before going on to a more technically oriented isolator manifolded doubles configuration. Don't make it into more than it is.

 

[DA Aquamaster]

As I am just moving up to doubles this thread has been particularly timely.
My tech instructor is a world class diver, published author, big dives... Doria, cave exploration, etc.
While advocating flexibility in choosing various configurations under different circumstances, I was surprised to learn his personal preference. He dives manifolded doubles but with the isolator CLOSED, diving them as independent doubles.

His vast experience notwithstanding, this sounded kind of nuts to me, simply because I had never heard of the practice in my fairly extensive reading. After following this discussion, it actually now seems like a way to reap the benefits of both systems.
Half the gas is saved as the default, no action required. But all the gas can be accessed in the event of the far more probable regulator failure.

Has anyone else heard of this? What do you think about it?

Avra

You are right in that it can allow you to get the benefits of independent doubles but if needed still access the contents of both tanks with either reg.

In a sense, the isolator only gets used after you have had a manifold or tank related failure, so it is in the real world going to be seldom used for any purpose other than to isolate the tanks first in the event you have doubts about where a massive leak lies and whether shutting down a post will resolve it. If you are deep or in a cve where you need to retain at least a third of your gas to exit safely, isolating first and working the problem later may make some sense and take some of the time pressure off. A blown burst disc can empty a tank very quickly and can empty both tansk in a very short period of time if you do not isolate quickly, so if I have a big leak that is not specifically coming out a second stage, I'll assume the worst and isolate first.

Some divers take the middle road approach and leave the isolator only slightly open (a twist or two compared to the seven or so twists needed to fully open and close it) which is enough to equalize the tanks but not so far as to take much time to close. Roll offs are common on the left post (the one you will need if your buddy goes OOA and takes your primary, so I check it every time I contact the overhead) but are not real common with the isolator, so there is probably some merit to that approach. But if it does roll all the way off, you will be breathing out of the right tank and reading pressure off the left tank, so you need to check the SPG often and stay sharp to notice the SPG is not dropping as expected and/or recheck the isolator after any contact with the overhead.

The major drawback with independent doubles and a long hose primary philosophy is that you may be on the bungee backup when the OOA buddy comes calling so if he/she goes for the reg in your mouth, life can get interesting since it is not going far with the bungee around your neck.

But then again a similar but less serious issue exists when diving with a side mount buddy - you need to know which side the long hose is on, where it is at at the moment and how to access it, so it becomes a training and familiarity issue.

In the end, as stated above it depends on a number of conditions and the specific situation, but like diving independent doubles, it makes the most sense if you have an actual reason for doing it that way rather than doing it "just becasue".