How to configure independent doubles

[DA Aquamaster]

I should add that if you dive independent doubles it is a good idea to use or make your second stages visually and tactilely different.

I use a matching yellow hose protector where the LP hose attaches to the second stage and another one where the HP hose attaches to the SPG on the reg on the right tank and use nothing on the reg on the left tank. I always know what one I am breathing off and I know that the second stage in my mouth matches the SPG I am looking at. It avoids confusion at depth and reduces task loading.

I use a bolt snap attached to a fairly heavy o-ring around the base of the mouth piece. This keeps the not-in-use second stage clipped to a D-ring even after the most violent of entries and keeps things streamlined. But it still keeps it immediately available if you or your buddy need it right now and do not have time to unclip it. The SPG on the right is also attached with a bolt snap to a D-ring which keeps it out of the way but still visible.

I route both the second stage hoses over the right shoulder which facilitates switching and with a little practice you can remove, clip, unclip and insert the regs with one hand with only a very slight pause in yoru normal breathing cycle. It's not DIR but with proper attention to hose lenght it is very user freindly and very streamlined.

 

[MikeFerrara]

It sounds like a cluttered configuration to me. I can see it getting really complicated when wearing a couple decompression cylinders and a stage or two.

When you're not solo which reg do you donate?
Do you use a long hose?
How do you secure the reg you're not using?

 

[Tanto]

I've been using indipendent doubles for thirteen years now, configured as follows (seen from above a diver facing ahead):

1) left tank has valve knob at 10, three parallel hoses leave at 2, one is reg, one is SPG, one is drysuit inflation; if using dual bladded BC there's a fourth hose for it as second inflator is on the right.
2) right tank has valve knob at 2, three parallel hoses at 10, one is reg, one is LP BC inflator, one is SPG.
3) both regs are attached to the neck, SPGs are attached to a side D-ring, hoses to drysuit and inflators
4) hoses cross behind the head; no hose protrudes outside

Mostly dive solo, never with buddy, but if needed can donate either reg, no long hose.
I like it and I am very comfortable with it.

 

[DA Aquamaster]

MikeFerrara once bubbled...
It sounds like a cluttered configuration to me. I can see it getting really complicated when wearing a couple decompression cylinders and a stage or two.

It's not - you have the same number of LP hoses and stages you have with manifolded doubles. The only additional piece of kit is an extra SPG. The clutter isse is not an issue - anymore than it is anyway with stage or deco bottles.

When you're not solo which reg do you donate?

In the two air sharing situations I have been involved with in the real world, I used my alternate second stage as the primary was ripped out of my mouth by a diver in no mood to follow the normal air share signal ettiquette. So I plan on donating the primary.

Do you use a long hose?

I don't dive a long hose as there really is not a need for me to use one. I don't do caves and the limited wreck penetration I do engage in is normally solo. If someone is gonna screw up and silt out the interior of a wreck I want it to be me.

The argument could be made that a long hose allows you to get some distance from an out of air diver sharing your air via a long hose. However in my real world experience the out of air diver benefits psychologically from some close face to face eye contact and I like to maintain close contact with the diver so I can take the lead in the managing the ascent - especially if the other diver is panicky. I have no desire to get drug to the surface by my long hose. This is not normally an issue as they usually have a death grip on my left shoulder strap.

I realize it is un-DIR to dive with a buddy you are not real comfortable with and who may not have adequate skills, but I am in a situation where I dive with a lot of fairly new or inexperienced divers.

My normal buddy on non-solo dives is an instructor and the dive team training officer. Consequenlty I am usually along on the deep AOW training dives and most of the deep dive rescue team training dives to follow up the group and ensure there are no stragglers. If someone gets lost or has a problem I am usually the one who gets to assist. I can't say I always enjoy diving with some of these buddies and I trust almost none of them, but if we don't dive with them where exactly are they supposed to get the experience?

In a hard overhead tech situation with a reliable buddy a long hose makes sense if you need to exit in trail formation so if I dove in caves etc, I would reconfigure with a long hose. This is not a problem with independent doubles as the hose is routed the same way as it would be with manifolded doubles and can still be clipped off on a D-ring when not in use. In that situation you would also have the option of donating either the long or short hose, the only difference being the long hose may not neccesarily be the one in your mouth at the time.

Understand what I am saying here though...I am flexible enough in my configuration to adapt it to the situation. If I lived in Florida and did a lot of diving I would dig the three sets of bands and manifolds I own out of the closet and would have 3 sets of manifolded doubles. I am advocating that independent doubles work exceptonally well for me and type of diving I do and offers some advantage over manifolded doubles. I am not saying they are the end all answer for everybody else or for every diving situation.

I am also indirectly advocating for the right for each and every diver to make intelligent and informed decisions about their individual configuration. I feel that we will lose a lot as a community if we all adopt an agency approved cookie cutter approach to gear configuration.

How do you secure the reg you're not using?

It was covered before but I'll repeat it. The not-currently-in-use second stage is secured with a bolt snap attached via an O-ring arouns the base of the mouth piece. It can be clipped and unclipped to a D-ring in normal use and can be pulled free easily with a sharp tug in an emergeny when someone needs it right now.

I have a center pocket on the waist strap and have a D ring attached there. Both second stage hoses are just long enough to reach the D-ring and are clipped to it when not in use. The right side SPG also clips to this. There is no extra hose lenght to deal with and they lie flat against myu shoulder and down the front of my chest. It is very streamlined and there is no hose hanging out in space. It is actually more streamlined than having the alternate second stage dangling on a necklace.

If you prefer a surgical tube or bungee necklace could be used for both but I don't prefer to do this as my method involves less clutter and keeps the "short" hose closer to my body.

As Tanto points out, hose routing is very efficient particulary with some attention to proper hose lenghts.

 

[toodles]

Just thought I would throw this in....

Independants are the way to go.
I would agree that it takes a lot of discipline to dive this
way, however the benefits outweigh the negatives.

Sure, you are going to have to put up with more SPG.
Big Deal.
Would you rather dive with a isolation manifold and in the event of a first stage failure on your left post you would not know how much air you would have for the remaining portion of your dive?
I would choose NO.

The arguement that the hoses are not as streamlined is not a valid one either. I will admit that there are some first stages out there that do not have the best ports for hose routing but with proper research you will find certain ones.
I recommend the Apeks DS4 for independants.

On my left post I have on my first stage my BCD inflator hose, my SPG, and my 7 foot stuffed hose attached in front, along with my primary second stage.
On my right post I have my drysuit hose, my SPG, and my secondary second stage.
All hoses are practically pointed straight down from my first stage.
It is very clean.
I use a necklace to hold both my primary & secondary regs.
They are clearly marked along with my SPG'S to avoid mistakes.

My 7 foot hose is attached very streamlined near my left shoulder on top out of the way of any deco bottles.

I do not believe in donating my primary in an OOA emergency for several reasons. Having my 7 foot hose in the place where it is, an OOA diver can see it from not only from the front and side, BUT
also very accessible from behind also. (if I was diving with 7 foot primary in mouth and my buddy was behind and needed air fast, would he be wasting time to get your attention first?)

As far as gas is concerned, use the rule of thirds.
Yes you do have to moniter two SPG'S.
What's the big deal? Most of the time you will only do one switch on your back gas underwater.

Doesn't it seem odd that it's OK to do a gas switch to your deco
gas, but it's WAY TOO COMPLICATED to do a switch on your backgas?
Diving independants is very easy.
It's just a lot of people will not admit that they cannot do it very well so they preach that it is difficult or too much task loading.

To them I ask, IS IT REALLT THAT BAD?
Don't you switch a reg every time you switch to deco?
You did it as your FIRST skill in your OW class!

these are just a few things to think about.
I could go into a lot more but no time.

Just make sure no matter how you configure your gear,
Think safety for yourself FIRST (by the way I do not solo dive)
Then think how to streamline your gear and dive it SAFE.

I have seen alot of CLEAN configurations out there.
I have seen alot of bird's nest's also.

Lean toward a clean configuration but do not jeopordize safety,
and remember think for yourself and do not let anyone think FOR you.

Good luck

 

[DA Aquamaster]

Well cool...the number of independent doubles divers on this board has just doubled. Welcome to the minority.

 

[matt_unique]

I have my PADI Master Diver cert and I'm mid-way through the TDI Deco Procedures course. I consider myself a novice relative to some of the people I dive with.

I am doing my course with single 120's with an H or Y valve and a 30CF deco bottle. The other students in my class are on doubles with the manifold and I don't buy it. I don't like the idea of the back gas supply being linked such that one leak anywhere in the system can empty your entire supply. Of course through the valve drills you learn to isolate the leak. I asked the instructor, if you had a leak would you really be able to tell which side it was coming from underwater. He said you would know but I wonder how obvious it would really be. I prefer the idea of just switching regs just as I would with a deco or pony bottle. I also like the idea of having an SPG on every tank.

Has anyone experienced a leak? Was it obvious where it was and you were able to isolate the leak on the first attempt?

--Matt

 

[DA Aquamaster]

Matt...I share your concern about the need to close a valve with manifolded doubles. But not because the leak may be hard to find. With a freeflowing second stage it's easy to detemine what side needs to be shut off. With other minor leaks from leaky o-rings and burst discs it is potentially more difficult to locate but also less time critical. If you have to, you do what it takes to see the problem and then close the correct valve which may not actually stop the leak (leaky burst disc, neck o-ring etc).

I normally dive in very cold water and with high performance regs. The biggest risk I face is a frozen first stage which will result in a full open max effort free flow. I have had 2 in my diving career and the first one was with a MK 3 and took forever to dump the tank. The second occurred with a much higher performance Mk 15 first stage. Based on my previous experience and on the presence of a redundant air source, I did not get too excited but was then totally amazed at how fast it dumped the entire contents of a 72 cu ft tank at 140 ft. It was really impressive.

Had I been using manifolded doubles it would have arguably taken twice as long to lose all the air, but all the air would have been at risk if a timely effort was not successfully made to close the valve to the frozen reg or at least an isolator valve. Speed is quite literally life in that situation and it's a situation I prefer to avoid.

Consequently, my preference is to dive independent doubles as my entire air supply is never at risk from a single failure. It is a good idea to close the valve on the freeflowing reg as soon as possible as the valve can be turned back on and the remaining air accessed in a couple minutes after the ice thaws, but it is not absolutlely required as it would be anytime a manifold is involved.

In my case with predominantly deep cold water diving, the independent doubles configuration just makes the most sense to me. If the biggest risk of a failure was something else, I'd consider a different configuration.

 

[Tanto]

The issue of how fast a tank is emptied at depth is a very interesting one. I did some dry testing after a nitrox tank was emptied in a matter of seconds at 105 meters/344ft, then I discussed those results with an hydraulic engineer.
Depth increases substantially the emptying speed, and so does the reduction of density (i.e. using helium).
As crazy as it sounds, you can actually empty a 10/70 80cf stage at 330ft in about ten seconds, yes, 10 seconds, if the freeflowing regulator is a Jetstream, but it may take as long as 30 seconds or more with any el cheapo reg.
I know it sounds unbelievable, so for those of you as skeptical as I was, take an air filled (unless you enjoy dumping helium) 80cf tank in your garage, attach a Jetstream to it, open the DIN valve all the way and depress the membrane of the second stage and time how long it takes to empty the tank.
Then apply the laws of physics and determine what than would be with a 10/70 mix at 330 ft. Scary, isn't it?

One more reason to dive indipendent twins, as DAAquamaster suggested.

 

[DA Aquamaster]

I spent much of this year diving with a MK 20 D400 and MK 25 D400 on my tanks. I did not have any freeflows with either reg despite the questionable TIS kit but I was also never comfortable with the elevated risk of these regs in cold water compared to the virtual in freezability of a MK 10 with a properly maintained SPEC kit.

When I added the higher flow rate of the MK20/25 to the mix, I decided to go back to my Mk 10's as the MK 10 first stage has always demonstrated more than adequate gas delivery yet does not have the excessive and unnecessary (from a practical standpoint) flow rate of the Mk 20/25. The excessive flow rate increases the adibatic cooling load on the reg and further increases the air loss in a given amount of time in a free flow situation if the first stage does freeze.

So it is a technological step backward (about 20 years) but it is the right decision for my particular diving profiles and increases the margin of saftey both by reducing the potential of a freeflow and by minimizing the air loss without compromising the regulator performance needed at depth.

It's counter intuitive from a concrete linear thinking perspective, but faster or bigger is not always better and that reasoning makes perfect sense from a systems thinking perspective.